excel.py

"""
Module parse to/from Excel
"""

#----------------------------------------------------------------------
# ExcelFile class
import os
import datetime
import abc
import numpy as np

from pandas.core.frame import DataFrame
from pandas.io.parsers import TextParser
from pandas.io.common import _is_url, _urlopen, _validate_header_arg, get_filepath_or_buffer, _is_s3_url
from pandas.tseries.period import Period
from pandas import json
from pandas.compat import (map, zip, reduce, range, lrange, u, add_metaclass,
                           BytesIO, string_types)
from pandas.core import config
from pandas.core.common import pprint_thing
from pandas.util.decorators import Appender
import pandas.compat as compat
import pandas.compat.openpyxl_compat as openpyxl_compat
import pandas.core.common as com
from warnings import warn
from distutils.version import LooseVersion

__all__ = ["read_excel", "ExcelWriter", "ExcelFile"]

_writer_extensions = ["xlsx", "xls", "xlsm"]
_writers = {}


def register_writer(klass):
    """Adds engine to the excel writer registry. You must use this method to
    integrate with ``to_excel``. Also adds config options for any new
    ``supported_extensions`` defined on the writer."""
    if not compat.callable(klass):
        raise ValueError("Can only register callables as engines")
    engine_name = klass.engine
    _writers[engine_name] = klass
    for ext in klass.supported_extensions:
        if ext.startswith('.'):
            ext = ext[1:]
        if ext not in _writer_extensions:
            config.register_option("io.excel.%s.writer" % ext,
                                   engine_name, validator=str)
            _writer_extensions.append(ext)


def get_writer(engine_name):
    if engine_name == 'openpyxl':
        try:
            import openpyxl

            # with version-less openpyxl engine
            # make sure we make the intelligent choice for the user
            if LooseVersion(openpyxl.__version__) < '2.0.0':
                 return _writers['openpyxl1']
            elif LooseVersion(openpyxl.__version__) < '2.2.0':
                 return _writers['openpyxl20']
            else:
                 return _writers['openpyxl22']
        except ImportError:
            # fall through to normal exception handling below
            pass

    try:
        return _writers[engine_name]
    except KeyError:
        raise ValueError("No Excel writer '%s'" % engine_name)

def read_excel(io, sheetname=0, header=0, skiprows=None, skip_footer=0,
               index_col=None, names=None, parse_cols=None, parse_dates=False,
               date_parser=None, na_values=None, thousands=None,
               convert_float=True, has_index_names=None, converters=None,
               engine=None, **kwds):
    """
    Read an Excel table into a pandas DataFrame

    Parameters
    ----------
    io : string, file-like object, pandas ExcelFile, or xlrd workbook.
        The string could be a URL. Valid URL schemes include http, ftp, s3,
        and file. For file URLs, a host is expected. For instance, a local
        file could be file://localhost/path/to/workbook.xlsx
    sheetname : string, int, mixed list of strings/ints, or None, default 0

        Strings are used for sheet names, Integers are used in zero-indexed sheet
        positions.

        Lists of strings/integers are used to request multiple sheets.

        Specify None to get all sheets.

        str|int -> DataFrame is returned.
        list|None -> Dict of DataFrames is returned, with keys representing sheets.

        Available Cases

        * Defaults to 0 -> 1st sheet as a DataFrame
        * 1 -> 2nd sheet as a DataFrame
        * "Sheet1" -> 1st sheet as a DataFrame
        * [0,1,"Sheet5"] -> 1st, 2nd & 5th sheet as a dictionary of DataFrames
        * None -> All sheets as a dictionary of DataFrames

    header : int, list of ints, default 0
        Row (0-indexed) to use for the column labels of the parsed
        DataFrame. If a list of integers is passed those row positions will
        be combined into a ``MultiIndex``
    skiprows : list-like
        Rows to skip at the beginning (0-indexed)
    skip_footer : int, default 0
        Rows at the end to skip (0-indexed)
    index_col : int, list of ints, default None
        Column (0-indexed) to use as the row labels of the DataFrame.
        Pass None if there is no such column.  If a list is passed,
        those columns will be combined into a ``MultiIndex``
    names : array-like, default None
        List of column names to use. If file contains no header row,
        then you should explicitly pass header=None
    converters : dict, default None
        Dict of functions for converting values in certain columns. Keys can
        either be integers or column labels, values are functions that take one
        input argument, the Excel cell content, and return the transformed
        content.
    parse_cols : int or list, default None
        * If None then parse all columns,
        * If int then indicates last column to be parsed
        * If list of ints then indicates list of column numbers to be parsed
        * If string then indicates comma separated list of column names and
          column ranges (e.g. "A:E" or "A,C,E:F")
    na_values : list-like, default None
        List of additional strings to recognize as NA/NaN
    thousands : str, default None
        Thousands separator for parsing string columns to numeric.  Note that
        this parameter is only necessary for columns stored as TEXT in Excel,
        any numeric columns will automatically be parsed, regardless of display
        format.
    keep_default_na : bool, default True
        If na_values are specified and keep_default_na is False the default NaN
        values are overridden, otherwise they're appended to
    verbose : boolean, default False
        Indicate number of NA values placed in non-numeric columns
    engine: string, default None
        If io is not a buffer or path, this must be set to identify io.
        Acceptable values are None or xlrd
    convert_float : boolean, default True
        convert integral floats to int (i.e., 1.0 --> 1). If False, all numeric
        data will be read in as floats: Excel stores all numbers as floats
        internally
    has_index_names : boolean, default None
        DEPRECATED: for version 0.17+ index names will be automatically inferred
        based on index_col.  To read Excel output from 0.16.2 and prior that
        had saved index names, use True.

    Returns
    -------
    parsed : DataFrame or Dict of DataFrames
        DataFrame from the passed in Excel file.  See notes in sheetname argument
        for more information on when a Dict of Dataframes is returned.

    """

    if not isinstance(io, ExcelFile):
        io = ExcelFile(io, engine=engine)

    return io._parse_excel(
        sheetname=sheetname, header=header, skiprows=skiprows,
        index_col=index_col, parse_cols=parse_cols, parse_dates=parse_dates,
        date_parser=date_parser, na_values=na_values, thousands=thousands,
        convert_float=convert_float, has_index_names=has_index_names,
        skip_footer=skip_footer, converters=converters, **kwds)

class ExcelFile(object):
    """
    Class for parsing tabular excel sheets into DataFrame objects.
    Uses xlrd. See read_excel for more documentation

    Parameters
    ----------
    io : string, file-like object or xlrd workbook
        If a string, expected to be a path to xls or xlsx file
    engine: string, default None
        If io is not a buffer or path, this must be set to identify io.
        Acceptable values are None or xlrd
    """
    def __init__(self, io, **kwds):

        import xlrd  # throw an ImportError if we need to

        ver = tuple(map(int, xlrd.__VERSION__.split(".")[:2]))
        if ver < (0, 9):  # pragma: no cover
            raise ImportError("pandas requires xlrd >= 0.9.0 for excel "
                              "support, current version " + xlrd.__VERSION__)

        self.io = io

        engine = kwds.pop('engine', None)

        if engine is not None and engine != 'xlrd':
            raise ValueError("Unknown engine: %s" % engine)

        if isinstance(io, compat.string_types):
            if _is_s3_url(io):
                buffer, _, _ = get_filepath_or_buffer(io)
                self.book = xlrd.open_workbook(file_contents=buffer.read())
            elif _is_url(io):
                data = _urlopen(io).read()
                self.book = xlrd.open_workbook(file_contents=data)
            else:
                self.book = xlrd.open_workbook(io)
        elif engine == 'xlrd' and isinstance(io, xlrd.Book):
            self.book = io
        elif not isinstance(io, xlrd.Book) and hasattr(io, "read"):
            # N.B. xlrd.Book has a read attribute too
            data = io.read()
            self.book = xlrd.open_workbook(file_contents=data)
        else:
            raise ValueError('Must explicitly set engine if not passing in'
                             ' buffer or path for io.')

    def parse(self, sheetname=0, header=0, skiprows=None, skip_footer=0,
              index_col=None, parse_cols=None, parse_dates=False,
              date_parser=None, na_values=None, thousands=None,
              convert_float=True, has_index_names=None, converters=None, **kwds):
        """
        Parse specified sheet(s) into a DataFrame

        Equivalent to read_excel(ExcelFile, ...)  See the read_excel
        docstring for more info on accepted parameters
        """

        return self._parse_excel(sheetname=sheetname, header=header,
                                 skiprows=skiprows,
                                 index_col=index_col,
                                 has_index_names=has_index_names,
                                 parse_cols=parse_cols,
                                 parse_dates=parse_dates,
                                 date_parser=date_parser, na_values=na_values,
                                 thousands=thousands,
                                 skip_footer=skip_footer,
                                 convert_float=convert_float,
                                 converters=converters,
                                 **kwds)

    def _should_parse(self, i, parse_cols):

        def _range2cols(areas):
            """
            Convert comma separated list of column names and column ranges to a
            list of 0-based column indexes.

            >>> _range2cols('A:E')
            [0, 1, 2, 3, 4]
            >>> _range2cols('A,C,Z:AB')
            [0, 2, 25, 26, 27]
            """
            def _excel2num(x):
                "Convert Excel column name like 'AB' to 0-based column index"
                return reduce(lambda s, a: s * 26 + ord(a) - ord('A') + 1,
                              x.upper().strip(), 0) - 1

            cols = []
            for rng in areas.split(','):
                if ':' in rng:
                    rng = rng.split(':')
                    cols += lrange(_excel2num(rng[0]), _excel2num(rng[1]) + 1)
                else:
                    cols.append(_excel2num(rng))
            return cols

        if isinstance(parse_cols, int):
            return i <= parse_cols
        elif isinstance(parse_cols, compat.string_types):
            return i in _range2cols(parse_cols)
        else:
            return i in parse_cols

    def _parse_excel(self, sheetname=0, header=0, skiprows=None, skip_footer=0,
                     index_col=None, has_index_names=None, parse_cols=None,
                     parse_dates=False, date_parser=None, na_values=None,
                     thousands=None, convert_float=True,
                     verbose=False, **kwds):

        skipfooter = kwds.pop('skipfooter', None)
        if skipfooter is not None:
            skip_footer = skipfooter

        _validate_header_arg(header)
        if has_index_names is not None:
            warn("\nThe has_index_names argument is deprecated; index names "
                 "will be automatically inferred based on index_col.\n"
                 "This argmument is still necessary if reading Excel output "
                 "from 0.16.2 or prior with index names.", FutureWarning,
                 stacklevel=3)

        if 'chunksize' in kwds:
            raise NotImplementedError("chunksize keyword of read_excel "
                                      "is not implemented")
        if parse_dates:
            raise NotImplementedError("parse_dates keyword of read_excel "
                                      "is not implemented")

        if date_parser is not None:
            raise NotImplementedError("date_parser keyword of read_excel "
                                      "is not implemented")

        import xlrd
        from xlrd import (xldate, XL_CELL_DATE,
                          XL_CELL_ERROR, XL_CELL_BOOLEAN,
                          XL_CELL_NUMBER)

        epoch1904 = self.book.datemode

        def _parse_cell(cell_contents,cell_typ):
            """converts the contents of the cell into a pandas
               appropriate object"""

            if cell_typ == XL_CELL_DATE:
                if xlrd_0_9_3:
                    # Use the newer xlrd datetime handling.
                    cell_contents = xldate.xldate_as_datetime(cell_contents,
                                                              epoch1904)

                    # Excel doesn't distinguish between dates and time,
                    # so we treat dates on the epoch as times only.
                    # Also, Excel supports 1900 and 1904 epochs.
                    year = (cell_contents.timetuple())[0:3]
                    if ((not epoch1904 and year == (1899, 12, 31))
                            or (epoch1904 and year == (1904, 1, 1))):
                        cell_contents = datetime.time(cell_contents.hour,
                                              cell_contents.minute,
                                              cell_contents.second,
                                              cell_contents.microsecond)
                else:
                    # Use the xlrd <= 0.9.2 date handling.
                    dt = xldate.xldate_as_tuple(cell_contents, epoch1904)

                    if dt[0] < datetime.MINYEAR:
                        cell_contents = datetime.time(*dt[3:])
                    else:
                        cell_contents = datetime.datetime(*dt)

            elif cell_typ == XL_CELL_ERROR:
                cell_contents = np.nan
            elif cell_typ == XL_CELL_BOOLEAN:
                cell_contents = bool(cell_contents)
            elif convert_float and cell_typ == XL_CELL_NUMBER:
                # GH5394 - Excel 'numbers' are always floats
                # it's a minimal perf hit and less suprising
                val = int(cell_contents)
                if val == cell_contents:
                    cell_contents = val
            return cell_contents

        # xlrd >= 0.9.3 can return datetime objects directly.
        if LooseVersion(xlrd.__VERSION__) >= LooseVersion("0.9.3"):
            xlrd_0_9_3 = True
        else:
            xlrd_0_9_3 = False

        ret_dict = False

        #Keep sheetname to maintain backwards compatibility.
        if isinstance(sheetname, list):
            sheets = sheetname
            ret_dict = True
        elif sheetname is None:
            sheets = self.sheet_names
            ret_dict = True
        else:
            sheets = [sheetname]

        #handle same-type duplicates.
        sheets = list(set(sheets))

        output = {}

        for asheetname in sheets:
            if verbose:
                print("Reading sheet %s" % asheetname)

            if isinstance(asheetname, compat.string_types):
                sheet = self.book.sheet_by_name(asheetname)
            else:  # assume an integer if not a string
                sheet = self.book.sheet_by_index(asheetname)

            data = []
            should_parse = {}

            for i in range(sheet.nrows):
                row = []
                for j, (value, typ) in enumerate(zip(sheet.row_values(i),
                                                     sheet.row_types(i))):
                    if parse_cols is not None and j not in should_parse:
                        should_parse[j] = self._should_parse(j, parse_cols)

                    if parse_cols is None or should_parse[j]:
                        row.append(_parse_cell(value,typ))
                data.append(row)

            if sheet.nrows == 0:
                output[asheetname] = DataFrame()
                continue

            if com.is_list_like(header) and len(header) == 1:
                header = header[0]

            # forward fill and pull out names for MultiIndex column
            header_names = None
            if header is not None:
                if com.is_list_like(header):
                    header_names = []
                    for row in header:
                        if com.is_integer(skiprows):
                            row += skiprows
                        data[row] = _fill_mi_header(data[row])
                        header_name, data[row] = _pop_header_name(data[row], index_col)
                        header_names.append(header_name)
                else:
                    data[header] = _trim_excel_header(data[header])

            if com.is_list_like(index_col):
                # forward fill values for MultiIndex index
                if not com.is_list_like(header):
                    offset = 1 + header
                else:
                    offset = 1 + max(header)

                for col in index_col:
                    last = data[offset][col]
                    for row in range(offset + 1, len(data)):
                        if data[row][col] == '' or data[row][col] is None:
                            data[row][col] = last
                        else:
                            last = data[row][col]

            if com.is_list_like(header) and len(header) > 1:
                has_index_names = True

            parser = TextParser(data, header=header, index_col=index_col,
                                has_index_names=has_index_names,
                                na_values=na_values,
                                thousands=thousands,
                                parse_dates=parse_dates,
                                date_parser=date_parser,
                                skiprows=skiprows,
                                skip_footer=skip_footer,
                                **kwds)

            output[asheetname] = parser.read()
            output[asheetname].columns = output[asheetname].columns.set_names(header_names)

        if ret_dict:
            return output
        else:
            return output[asheetname]


    @property
    def sheet_names(self):
        return self.book.sheet_names()

    def close(self):
        """close io if necessary"""
        if hasattr(self.io, 'close'):
            self.io.close()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.close()


def _trim_excel_header(row):
    # trim header row so auto-index inference works
    # xlrd uses '' , openpyxl None
    while len(row) > 0 and (row[0] == '' or row[0] is None):
        row = row[1:]
    return row

def _fill_mi_header(row):
    # forward fill blanks entries
    # from headers if parsing as MultiIndex
    last = row[0]
    for i in range(1, len(row)):
        if row[i] == '' or row[i] is None:
            row[i] = last
        else:
            last = row[i]
    return row

# fill blank if index_col not None
def _pop_header_name(row, index_col):
    """ (header, new_data) for header rows in MultiIndex parsing"""
    none_fill = lambda x: None if x == '' else x

    if index_col is None:
        # no index col specified, trim data for inference path
        return none_fill(row[0]), row[1:]
    else:
        # pop out header name and fill w/ blank
        i = index_col if not com.is_list_like(index_col) else max(index_col)
        return none_fill(row[i]), row[:i] + [''] + row[i+1:]

def _conv_value(val):
    # Convert numpy types to Python types for the Excel writers.
    if com.is_integer(val):
        val = int(val)
    elif com.is_float(val):
        val = float(val)
    elif com.is_bool(val):
        val = bool(val)
    elif isinstance(val, Period):
        val = "%s" % val
    elif com.is_list_like(val):
        val = str(val)

    return val


@add_metaclass(abc.ABCMeta)
class ExcelWriter(object):
    """
    Class for writing DataFrame objects into excel sheets, default is to use
    xlwt for xls, openpyxl for xlsx.  See DataFrame.to_excel for typical usage.

    Parameters
    ----------
    path : string
        Path to xls or xlsx file.
    engine : string (optional)
        Engine to use for writing. If None, defaults to
        ``io.excel.<extension>.writer``.  NOTE: can only be passed as a keyword
        argument.
    date_format : string, default None
        Format string for dates written into Excel files (e.g. 'YYYY-MM-DD')
    datetime_format : string, default None
        Format string for datetime objects written into Excel files
        (e.g. 'YYYY-MM-DD HH:MM:SS')

    Notes
    -----
    For compatibility with CSV writers, ExcelWriter serializes lists
    and dicts to strings before writing.
    """
    # Defining an ExcelWriter implementation (see abstract methods for more...)

    # - Mandatory
    #   - ``write_cells(self, cells, sheet_name=None, startrow=0, startcol=0)``
    #     --> called to write additional DataFrames to disk
    #   - ``supported_extensions`` (tuple of supported extensions), used to
    #      check that engine supports the given extension.
    #   - ``engine`` - string that gives the engine name. Necessary to
    #     instantiate class directly and bypass ``ExcelWriterMeta`` engine
    #     lookup.
    #   - ``save(self)`` --> called to save file to disk
    # - Mostly mandatory (i.e. should at least exist)
    #   - book, cur_sheet, path

    # - Optional:
    #   - ``__init__(self, path, engine=None, **kwargs)`` --> always called
    #     with path as first argument.

    # You also need to register the class with ``register_writer()``.
    # Technically, ExcelWriter implementations don't need to subclass
    # ExcelWriter.
    def __new__(cls, path, engine=None, **kwargs):
        # only switch class if generic(ExcelWriter)
        if issubclass(cls, ExcelWriter):
            if engine is None:
                if isinstance(path, string_types):
                    ext = os.path.splitext(path)[-1][1:]
                else:
                    ext = 'xlsx'

                try:
                    engine = config.get_option('io.excel.%s.writer' % ext)
                except KeyError:
                    error = ValueError("No engine for filetype: '%s'" % ext)
                    raise error
            cls = get_writer(engine)

        return object.__new__(cls)

    # declare external properties you can count on
    book = None
    curr_sheet = None
    path = None

    @abc.abstractproperty
    def supported_extensions(self):
        "extensions that writer engine supports"
        pass

    @abc.abstractproperty
    def engine(self):
        "name of engine"
        pass

    @abc.abstractmethod
    def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
        """
        Write given formated cells into Excel an excel sheet

        Parameters
        ----------
        cells : generator
            cell of formated data to save to Excel sheet
        sheet_name : string, default None
            Name of Excel sheet, if None, then use self.cur_sheet
        startrow: upper left cell row to dump data frame
        startcol: upper left cell column to dump data frame
        """
        pass

    @abc.abstractmethod
    def save(self):
        """
        Save workbook to disk.
        """
        pass

    def __init__(self, path, engine=None,
                 date_format=None, datetime_format=None, **engine_kwargs):
        # validate that this engine can handle the extension
        if isinstance(path, string_types):
            ext = os.path.splitext(path)[-1]
        else:
            ext = 'xls' if engine == 'xlwt' else 'xlsx'

        self.check_extension(ext)

        self.path = path
        self.sheets = {}
        self.cur_sheet = None

        if date_format is None:
            self.date_format = 'YYYY-MM-DD'
        else:
            self.date_format = date_format
        if datetime_format is None:
            self.datetime_format = 'YYYY-MM-DD HH:MM:SS'
        else:
            self.datetime_format = datetime_format

    def _get_sheet_name(self, sheet_name):
        if sheet_name is None:
            sheet_name = self.cur_sheet
        if sheet_name is None:  # pragma: no cover
            raise ValueError('Must pass explicit sheet_name or set '
                             'cur_sheet property')
        return sheet_name

    @classmethod
    def check_extension(cls, ext):
        """checks that path's extension against the Writer's supported
        extensions.  If it isn't supported, raises UnsupportedFiletypeError."""
        if ext.startswith('.'):
            ext = ext[1:]
        if not any(ext in extension for extension in cls.supported_extensions):
            msg = (u("Invalid extension for engine '%s': '%s'") %
                   (pprint_thing(cls.engine), pprint_thing(ext)))
            raise ValueError(msg)
        else:
            return True

    # Allow use as a contextmanager
    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.close()

    def close(self):
        """synonym for save, to make it more file-like"""
        return self.save()


class _Openpyxl1Writer(ExcelWriter):
    engine = 'openpyxl1'
    supported_extensions = ('.xlsx', '.xlsm')
    openpyxl_majorver = 1

    def __init__(self, path, engine=None, **engine_kwargs):
        if not openpyxl_compat.is_compat(major_ver=self.openpyxl_majorver):
            raise ValueError('Installed openpyxl is not supported at this '
                             'time. Use {0}.x.y.'
                             .format(self.openpyxl_majorver))
        # Use the openpyxl module as the Excel writer.
        from openpyxl.workbook import Workbook

        super(_Openpyxl1Writer, self).__init__(path, **engine_kwargs)

        # Create workbook object with default optimized_write=True.
        self.book = Workbook()
        # Openpyxl 1.6.1 adds a dummy sheet. We remove it.
        if self.book.worksheets:
            self.book.remove_sheet(self.book.worksheets[0])

    def save(self):
        """
        Save workbook to disk.
        """
        return self.book.save(self.path)

    def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
        # Write the frame cells using openpyxl.
        from openpyxl.cell import get_column_letter

        sheet_name = self._get_sheet_name(sheet_name)

        if sheet_name in self.sheets:
            wks = self.sheets[sheet_name]
        else:
            wks = self.book.create_sheet()
            wks.title = sheet_name
            self.sheets[sheet_name] = wks

        for cell in cells:
            colletter = get_column_letter(startcol + cell.col + 1)
            xcell = wks.cell("%s%s" % (colletter, startrow + cell.row + 1))
            if (isinstance(cell.val, compat.string_types)
                    and xcell.data_type_for_value(cell.val)
                         != xcell.TYPE_STRING):
                xcell.set_value_explicit(cell.val)
            else:
                xcell.value = _conv_value(cell.val)
            style = None
            if cell.style:
                style = self._convert_to_style(cell.style)
                for field in style.__fields__:
                    xcell.style.__setattr__(field,
                                            style.__getattribute__(field))

            if isinstance(cell.val, datetime.datetime):
                xcell.style.number_format.format_code = self.datetime_format
            elif isinstance(cell.val, datetime.date):
                xcell.style.number_format.format_code = self.date_format

            if cell.mergestart is not None and cell.mergeend is not None:
                cletterstart = get_column_letter(startcol + cell.col + 1)
                cletterend = get_column_letter(startcol + cell.mergeend + 1)

                wks.merge_cells('%s%s:%s%s' % (cletterstart,
                                               startrow + cell.row + 1,
                                               cletterend,
                                               startrow + cell.mergestart + 1))

                # Excel requires that the format of the first cell in a merged
                # range is repeated in the rest of the merged range.
                if style:
                    first_row = startrow + cell.row + 1
                    last_row = startrow + cell.mergestart + 1
                    first_col = startcol + cell.col + 1
                    last_col = startcol + cell.mergeend + 1

                    for row in range(first_row, last_row + 1):
                        for col in range(first_col, last_col + 1):
                            if row == first_row and col == first_col:
                                # Ignore first cell. It is already handled.
                                continue
                            colletter = get_column_letter(col)
                            xcell = wks.cell("%s%s" % (colletter, row))
                            for field in style.__fields__:
                                xcell.style.__setattr__(
                                    field, style.__getattribute__(field))

    @classmethod
    def _convert_to_style(cls, style_dict):
        """
        converts a style_dict to an openpyxl style object
        Parameters
        ----------
        style_dict: style dictionary to convert
        """

        from openpyxl.style import Style
        xls_style = Style()
        for key, value in style_dict.items():
            for nk, nv in value.items():
                if key == "borders":
                    (xls_style.borders.__getattribute__(nk)
                     .__setattr__('border_style', nv))
                else:
                    xls_style.__getattribute__(key).__setattr__(nk, nv)

        return xls_style

register_writer(_Openpyxl1Writer)


class _OpenpyxlWriter(_Openpyxl1Writer):
    engine = 'openpyxl'

register_writer(_OpenpyxlWriter)


class _Openpyxl20Writer(_Openpyxl1Writer):
    """
    Note: Support for OpenPyxl v2 is currently EXPERIMENTAL (GH7565).
    """
    engine = 'openpyxl20'
    openpyxl_majorver = 2

    def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
        # Write the frame cells using openpyxl.
        from openpyxl.cell import get_column_letter

        sheet_name = self._get_sheet_name(sheet_name)

        if sheet_name in self.sheets:
            wks = self.sheets[sheet_name]
        else:
            wks = self.book.create_sheet()
            wks.title = sheet_name
            self.sheets[sheet_name] = wks

        for cell in cells:
            colletter = get_column_letter(startcol + cell.col + 1)
            xcell = wks.cell("%s%s" % (colletter, startrow + cell.row + 1))
            xcell.value = _conv_value(cell.val)
            style_kwargs = {}

            # Apply format codes before cell.style to allow override
            if isinstance(cell.val, datetime.datetime):
                style_kwargs.update(self._convert_to_style_kwargs({
                        'number_format':{'format_code': self.datetime_format}}))
            elif isinstance(cell.val, datetime.date):
                style_kwargs.update(self._convert_to_style_kwargs({
                        'number_format':{'format_code': self.date_format}}))

            if cell.style:
                style_kwargs.update(self._convert_to_style_kwargs(cell.style))

            if style_kwargs:
                xcell.style = xcell.style.copy(**style_kwargs)

            if cell.mergestart is not None and cell.mergeend is not None:
                cletterstart = get_column_letter(startcol + cell.col + 1)
                cletterend = get_column_letter(startcol + cell.mergeend + 1)

                wks.merge_cells('%s%s:%s%s' % (cletterstart,
                                               startrow + cell.row + 1,
                                               cletterend,
                                               startrow + cell.mergestart + 1))

                # Excel requires that the format of the first cell in a merged
                # range is repeated in the rest of the merged range.
                if style_kwargs:
                    first_row = startrow + cell.row + 1
                    last_row = startrow + cell.mergestart + 1
                    first_col = startcol + cell.col + 1
                    last_col = startcol + cell.mergeend + 1

                    for row in range(first_row, last_row + 1):
                        for col in range(first_col, last_col + 1):
                            if row == first_row and col == first_col:
                                # Ignore first cell. It is already handled.
                                continue
                            colletter = get_column_letter(col)
                            xcell = wks.cell("%s%s" % (colletter, row))
                            xcell.style = xcell.style.copy(**style_kwargs)

    @classmethod
    def _convert_to_style_kwargs(cls, style_dict):
        """
        Convert a style_dict to a set of kwargs suitable for initializing
        or updating-on-copy an openpyxl v2 style object
        Parameters
        ----------
        style_dict : dict
            A dict with zero or more of the following keys (or their synonyms).
                'font'
                'fill'
                'border' ('borders')
                'alignment'
                'number_format'
                'protection'
        Returns
        -------
        style_kwargs : dict
            A dict with the same, normalized keys as ``style_dict`` but each
            value has been replaced with a native openpyxl style object of the
            appropriate class.
        """

        _style_key_map = {
            'borders': 'border',
        }

        style_kwargs = {}
        for k, v in style_dict.items():
            if k in _style_key_map:
                k = _style_key_map[k]
            _conv_to_x = getattr(cls, '_convert_to_{0}'.format(k),
                    lambda x: None)
            new_v = _conv_to_x(v)
            if new_v:
                style_kwargs[k] = new_v

        return style_kwargs


    @classmethod
    def _convert_to_color(cls, color_spec):
        """
        Convert ``color_spec`` to an openpyxl v2 Color object
        Parameters
        ----------
        color_spec : str, dict
            A 32-bit ARGB hex string, or a dict with zero or more of the
            following keys.
                'rgb'
                'indexed'
                'auto'
                'theme'
                'tint'
                'index'
                'type'
        Returns
        -------
        color : openpyxl.styles.Color
        """

        from openpyxl.styles import Color

        if isinstance(color_spec, str):
            return Color(color_spec)
        else:
            return Color(**color_spec)


    @classmethod
    def _convert_to_font(cls, font_dict):
        """
        Convert ``font_dict`` to an openpyxl v2 Font object
        Parameters
        ----------
        font_dict : dict
            A dict with zero or more of the following keys (or their synonyms).
                'name'
                'size' ('sz')
                'bold' ('b')
                'italic' ('i')
                'underline' ('u')
                'strikethrough' ('strike')
                'color'
                'vertAlign' ('vertalign')
                'charset'
                'scheme'
                'family'
                'outline'
                'shadow'
                'condense'
        Returns
        -------
        font : openpyxl.styles.Font
        """

        from openpyxl.styles import Font

        _font_key_map = {
            'sz': 'size',
            'b': 'bold',
            'i': 'italic',
            'u': 'underline',
            'strike': 'strikethrough',
            'vertalign': 'vertAlign',
        }

        font_kwargs = {}
        for k, v in font_dict.items():
            if k in _font_key_map:
                k = _font_key_map[k]
            if k == 'color':
                v = cls._convert_to_color(v)
            font_kwargs[k] = v

        return Font(**font_kwargs)


    @classmethod
    def _convert_to_stop(cls, stop_seq):
        """
        Convert ``stop_seq`` to a list of openpyxl v2 Color objects,
        suitable for initializing the ``GradientFill`` ``stop`` parameter.
        Parameters
        ----------
        stop_seq : iterable
            An iterable that yields objects suitable for consumption by
            ``_convert_to_color``.
        Returns
        -------
        stop : list of openpyxl.styles.Color
        """

        return map(cls._convert_to_color, stop_seq)


    @classmethod
    def _convert_to_fill(cls, fill_dict):
        """
        Convert ``fill_dict`` to an openpyxl v2 Fill object
        Parameters
        ----------
        fill_dict : dict
            A dict with one or more of the following keys (or their synonyms),
                'fill_type' ('patternType', 'patterntype')
                'start_color' ('fgColor', 'fgcolor')
                'end_color' ('bgColor', 'bgcolor')
            or one or more of the following keys (or their synonyms).
                'type' ('fill_type')
                'degree'
                'left'
                'right'
                'top'
                'bottom'
                'stop'
        Returns
        -------
        fill : openpyxl.styles.Fill
        """

        from openpyxl.styles import PatternFill, GradientFill

        _pattern_fill_key_map = {
            'patternType': 'fill_type',
            'patterntype': 'fill_type',
            'fgColor': 'start_color',
            'fgcolor': 'start_color',
            'bgColor': 'end_color',
            'bgcolor': 'end_color',
        }

        _gradient_fill_key_map = {
            'fill_type': 'type',
        }

        pfill_kwargs = {}
        gfill_kwargs = {}
        for k, v in fill_dict.items():
            pk = gk = None
            if k in _pattern_fill_key_map:
                pk = _pattern_fill_key_map[k]
            if k in _gradient_fill_key_map:
                gk = _gradient_fill_key_map[k]
            if pk in ['start_color', 'end_color']:
                v = cls._convert_to_color(v)
            if gk == 'stop':
                v = cls._convert_to_stop(v)
            if pk:
                pfill_kwargs[pk] = v
            elif gk:
                gfill_kwargs[gk] = v
            else:
                pfill_kwargs[k] = v
                gfill_kwargs[k] = v

        try:
            return PatternFill(**pfill_kwargs)
        except TypeError:
            return GradientFill(**gfill_kwargs)


    @classmethod
    def _convert_to_side(cls, side_spec):
        """
        Convert ``side_spec`` to an openpyxl v2 Side object
        Parameters
        ----------
        side_spec : str, dict
            A string specifying the border style, or a dict with zero or more
            of the following keys (or their synonyms).
                'style' ('border_style')
                'color'
        Returns
        -------
        side : openpyxl.styles.Side
        """

        from openpyxl.styles import Side

        _side_key_map = {
            'border_style': 'style',
        }

        if isinstance(side_spec, str):
            return Side(style=side_spec)

        side_kwargs = {}
        for k, v in side_spec.items():
            if k in _side_key_map:
                k = _side_key_map[k]
            if k == 'color':
                v = cls._convert_to_color(v)
            side_kwargs[k] = v

        return Side(**side_kwargs)


    @classmethod
    def _convert_to_border(cls, border_dict):
        """
        Convert ``border_dict`` to an openpyxl v2 Border object
        Parameters
        ----------
        border_dict : dict
            A dict with zero or more of the following keys (or their synonyms).
                'left'
                'right'
                'top'
                'bottom'
                'diagonal'
                'diagonal_direction'
                'vertical'
                'horizontal'
                'diagonalUp' ('diagonalup')
                'diagonalDown' ('diagonaldown')
                'outline'
        Returns
        -------
        border : openpyxl.styles.Border
        """

        from openpyxl.styles import Border

        _border_key_map = {
            'diagonalup': 'diagonalUp',
            'diagonaldown': 'diagonalDown',
        }

        border_kwargs = {}
        for k, v in border_dict.items():
            if k in _border_key_map:
                k = _border_key_map[k]
            if k == 'color':
                v = cls._convert_to_color(v)
            if k in ['left', 'right', 'top', 'bottom', 'diagonal']:
                v = cls._convert_to_side(v)
            border_kwargs[k] = v

        return Border(**border_kwargs)


    @classmethod
    def _convert_to_alignment(cls, alignment_dict):
        """
        Convert ``alignment_dict`` to an openpyxl v2 Alignment object
        Parameters
        ----------
        alignment_dict : dict
            A dict with zero or more of the following keys (or their synonyms).
                'horizontal'
                'vertical'
                'text_rotation'
                'wrap_text'
                'shrink_to_fit'
                'indent'
        Returns
        -------
        alignment : openpyxl.styles.Alignment
        """

        from openpyxl.styles import Alignment

        return Alignment(**alignment_dict)


    @classmethod
    def _convert_to_number_format(cls, number_format_dict):
        """
        Convert ``number_format_dict`` to an openpyxl v2.1.0 number format
        initializer.
        Parameters
        ----------
        number_format_dict : dict
            A dict with zero or more of the following keys.
                'format_code' : str
        Returns
        -------
        number_format : str
        """
        try:
            # >= 2.0.0 < 2.1.0
            from openpyxl.styles import NumberFormat
            return NumberFormat(**number_format_dict)
        except:
            # >= 2.1.0
            return number_format_dict['format_code']

    @classmethod
    def _convert_to_protection(cls, protection_dict):
        """
        Convert ``protection_dict`` to an openpyxl v2 Protection object.
        Parameters
        ----------
        protection_dict : dict
            A dict with zero or more of the following keys.
                'locked'
                'hidden'
        Returns
        -------
        """

        from openpyxl.styles import Protection

        return Protection(**protection_dict)


register_writer(_Openpyxl20Writer)

class _Openpyxl22Writer(_Openpyxl20Writer):
    """
    Note: Support for OpenPyxl v2.2 is currently EXPERIMENTAL (GH7565).
    """
    engine = 'openpyxl22'
    openpyxl_majorver = 2

    def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
        # Write the frame cells using openpyxl.
        from openpyxl import styles

        sheet_name = self._get_sheet_name(sheet_name)

        _style_cache = {}

        if sheet_name in self.sheets:
            wks = self.sheets[sheet_name]
        else:
            wks = self.book.create_sheet()
            wks.title = sheet_name
            self.sheets[sheet_name] = wks

        for cell in cells:
            xcell = wks.cell(
                        row=startrow + cell.row + 1,
                        column=startcol + cell.col + 1
                        )
            xcell.value = _conv_value(cell.val)

            style_kwargs = {}
            if cell.style:
                key = str(cell.style)
                style_kwargs = _style_cache.get(key)
                if style_kwargs is None:
                    style_kwargs = self._convert_to_style_kwargs(cell.style)
                    _style_cache[key] = style_kwargs

            if style_kwargs:
                for k, v in style_kwargs.items():
                    setattr(xcell, k, v)

            if cell.mergestart is not None and cell.mergeend is not None:

                wks.merge_cells(
                        start_row=startrow + cell.row + 1,
                        start_column=startcol + cell.col + 1,
                        end_column=startcol + cell.mergeend + 1,
                        end_row=startrow + cell.mergestart + 1
                        )

                # When cells are merged only the top-left cell is preserved
                # The behaviour of the other cells in a merged range is undefined
                if style_kwargs:
                    first_row = startrow + cell.row + 1
                    last_row = startrow + cell.mergestart + 1
                    first_col = startcol + cell.col + 1
                    last_col = startcol + cell.mergeend + 1

                    for row in range(first_row, last_row + 1):
                        for col in range(first_col, last_col + 1):
                            if row == first_row and col == first_col:
                                # Ignore first cell. It is already handled.
                                continue
                            xcell = wks.cell(column=col, row=row)
                            for k, v in style_kwargs.items():
                                setattr(xcell, k, v)

register_writer(_Openpyxl22Writer)

class _XlwtWriter(ExcelWriter):
    engine = 'xlwt'
    supported_extensions = ('.xls',)

    def __init__(self, path, engine=None, encoding=None, **engine_kwargs):
        # Use the xlwt module as the Excel writer.
        import xlwt
        engine_kwargs['engine'] = engine
        super(_XlwtWriter, self).__init__(path, **engine_kwargs)

        if encoding is None:
            encoding = 'ascii'
        self.book = xlwt.Workbook(encoding=encoding)
        self.fm_datetime = xlwt.easyxf(num_format_str=self.datetime_format)
        self.fm_date = xlwt.easyxf(num_format_str=self.date_format)

    def save(self):
        """
        Save workbook to disk.
        """
        return self.book.save(self.path)

    def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
        # Write the frame cells using xlwt.

        sheet_name = self._get_sheet_name(sheet_name)

        if sheet_name in self.sheets:
            wks = self.sheets[sheet_name]
        else:
            wks = self.book.add_sheet(sheet_name)
            self.sheets[sheet_name] = wks

        style_dict = {}

        for cell in cells:
            val = _conv_value(cell.val)

            num_format_str = None
            if isinstance(cell.val, datetime.datetime):
                num_format_str = self.datetime_format
            elif isinstance(cell.val, datetime.date):
                num_format_str = self.date_format

            stylekey = json.dumps(cell.style)
            if num_format_str:
                stylekey += num_format_str

            if stylekey in style_dict:
                style = style_dict[stylekey]
            else:
                style = self._convert_to_style(cell.style, num_format_str)
                style_dict[stylekey] = style

            if cell.mergestart is not None and cell.mergeend is not None:
                wks.write_merge(startrow + cell.row,
                                startrow + cell.mergestart,
                                startcol + cell.col,
                                startcol + cell.mergeend,
                                val, style)
            else:
                wks.write(startrow + cell.row,
                          startcol + cell.col,
                          val, style)

    @classmethod
    def _style_to_xlwt(cls, item, firstlevel=True, field_sep=',',
                       line_sep=';'):
        """helper which recursively generate an xlwt easy style string
        for example:

            hstyle = {"font": {"bold": True},
            "border": {"top": "thin",
                    "right": "thin",
                    "bottom": "thin",
                    "left": "thin"},
            "align": {"horiz": "center"}}
            will be converted to
            font: bold on; \
                    border: top thin, right thin, bottom thin, left thin; \
                    align: horiz center;
        """
        if hasattr(item, 'items'):
            if firstlevel:
                it = ["%s: %s" % (key, cls._style_to_xlwt(value, False))
                      for key, value in item.items()]
                out = "%s " % (line_sep).join(it)
                return out
            else:
                it = ["%s %s" % (key, cls._style_to_xlwt(value, False))
                      for key, value in item.items()]
                out = "%s " % (field_sep).join(it)
                return out
        else:
            item = "%s" % item
            item = item.replace("True", "on")
            item = item.replace("False", "off")
            return item

    @classmethod
    def _convert_to_style(cls, style_dict, num_format_str=None):
        """
        converts a style_dict to an xlwt style object
        Parameters
        ----------
        style_dict: style dictionary to convert
        num_format_str: optional number format string
        """
        import xlwt

        if style_dict:
            xlwt_stylestr = cls._style_to_xlwt(style_dict)
            style = xlwt.easyxf(xlwt_stylestr, field_sep=',', line_sep=';')
        else:
            style = xlwt.XFStyle()
        if num_format_str is not None:
            style.num_format_str = num_format_str

        return style

register_writer(_XlwtWriter)


class _XlsxWriter(ExcelWriter):
    engine = 'xlsxwriter'
    supported_extensions = ('.xlsx',)

    def __init__(self, path, engine=None,
                 date_format=None, datetime_format=None, **engine_kwargs):
        # Use the xlsxwriter module as the Excel writer.
        import xlsxwriter

        super(_XlsxWriter, self).__init__(path, engine=engine,
                                          date_format=date_format,
                                          datetime_format=datetime_format,
                                          **engine_kwargs)

        self.book = xlsxwriter.Workbook(path, **engine_kwargs)

    def save(self):
        """
        Save workbook to disk.
        """
        return self.book.close()

    def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
        # Write the frame cells using xlsxwriter.

        sheet_name = self._get_sheet_name(sheet_name)

        if sheet_name in self.sheets:
            wks = self.sheets[sheet_name]
        else:
            wks = self.book.add_worksheet(sheet_name)
            self.sheets[sheet_name] = wks

        style_dict = {}

        for cell in cells:
            val = _conv_value(cell.val)

            num_format_str = None
            if isinstance(cell.val, datetime.datetime):
                num_format_str = self.datetime_format
            elif isinstance(cell.val, datetime.date):
                num_format_str = self.date_format

            stylekey = json.dumps(cell.style)
            if num_format_str:
                stylekey += num_format_str

            if stylekey in style_dict:
                style = style_dict[stylekey]
            else:
                style = self._convert_to_style(cell.style, num_format_str)
                style_dict[stylekey] = style

            if cell.mergestart is not None and cell.mergeend is not None:
                wks.merge_range(startrow + cell.row,
                                startcol + cell.col,
                                startrow + cell.mergestart,
                                startcol + cell.mergeend,
                                cell.val, style)
            else:
                wks.write(startrow + cell.row,
                          startcol + cell.col,
                          val, style)

    def _convert_to_style(self, style_dict, num_format_str=None):
        """
        converts a style_dict to an xlsxwriter format object
        Parameters
        ----------
        style_dict: style dictionary to convert
        num_format_str: optional number format string
        """

        # If there is no formatting we don't create a format object.
        if num_format_str is None and style_dict is None:
            return None

        # Create a XlsxWriter format object.
        xl_format = self.book.add_format()

        if num_format_str is not None:
            xl_format.set_num_format(num_format_str)

        if style_dict is None:
            return xl_format

        # Map the cell font to XlsxWriter font properties.
        if style_dict.get('font'):
            font = style_dict['font']
            if font.get('bold'):
                xl_format.set_bold()

        # Map the alignment to XlsxWriter alignment properties.
        alignment = style_dict.get('alignment')
        if alignment:
            if (alignment.get('horizontal')
                    and alignment['horizontal'] == 'center'):
                xl_format.set_align('center')
            if (alignment.get('vertical')
                    and alignment['vertical'] == 'top'):
                xl_format.set_align('top')

        # Map the cell borders to XlsxWriter border properties.
        if style_dict.get('borders'):
            xl_format.set_border()

        return xl_format

register_writer(_XlsxWriter)