CLN: Remove unnecessary ExcelWriterMeta metaclass

Only `__new__` is really necessary. And subclasses just have to deal
with being passed an 'engine' keyword argument + a tad bit of style
cleanup.

Author: jtratner

pandas/io/excel.py

@@ -24,6 +24,7 @@
 _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
@@ -40,12 +41,14 @@ def register_writer(klass):
                                    engine_name, validator=str)
             _writer_extensions.append(ext)
 
+
 def get_writer(engine_name):
     try:
         return _writers[engine_name]
     except KeyError:
         raise ValueError("No Excel writer '%s'" % engine_name)
 
+
 def read_excel(io, sheetname, **kwds):
     """Read an Excel table into a pandas DataFrame
 
@@ -80,7 +83,7 @@ def read_excel(io, sheetname, **kwds):
     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
-        
+
     Returns
     -------
     parsed : DataFrame
@@ -90,9 +93,9 @@ def read_excel(io, sheetname, **kwds):
         kwds.pop('kind')
         warn("kind keyword is no longer supported in read_excel and may be "
              "removed in a future version", FutureWarning)
-    
-    engine = kwds.pop('engine', None)   
-        
+
+    engine = kwds.pop('engine', None)
+
     return ExcelFile(io, engine=engine).parse(sheetname=sheetname, **kwds)
 
 
@@ -119,9 +122,9 @@ def __init__(self, io, **kwds):
                               "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)
 
@@ -133,7 +136,8 @@ def __init__(self, io, **kwds):
             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.')            
+            raise ValueError('Must explicitly set engine if not passing in'
+                             ' buffer or path for io.')
 
     def parse(self, sheetname, header=0, skiprows=None, skip_footer=0,
               index_col=None, parse_cols=None, parse_dates=False,
@@ -291,13 +295,15 @@ def __enter__(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 _conv_value(val):
     # Convert numpy types to Python types for the Excel writers.
     if com.is_integer(val):
@@ -312,34 +318,45 @@ def _conv_value(val):
     return val
 
 
-class ExcelWriterMeta(abc.ABCMeta):
+@add_metaclass(abc.ABCMeta)
+class ExcelWriter(object):
     """
-    Metaclass that dynamically chooses the ExcelWriter to use.
-
-    If you directly instantiate a subclass, it skips the engine lookup.
-
-    Defining an ExcelWriter implementation (see abstract methods on ExcelWriter for more...).
-
-    - Mandatory (but not checked at run time):
-      - ``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
-    - Optional:
-      - ``__init__(self, path, **kwargs)`` --> always called with path as first
-        argument.
+    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.
 
-    You also need to register the class with ``register_writer()``.
+    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.
     """
-
-    def __call__(cls, path, **kwargs):
-        engine = kwargs.pop('engine', None)
-        # if it's not an ExcelWriter baseclass, dont' do anything (you've
-        # probably made an explicit choice here)
-        if not isinstance(getattr(cls, 'engine', None), compat.string_types):
+    # 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 cls == ExcelWriter:
             if engine is None:
                 ext = os.path.splitext(path)[-1][1:]
                 try:
@@ -348,31 +365,14 @@ def __call__(cls, path, **kwargs):
                     error = ValueError("No engine for filetype: '%s'" % ext)
                     raise error
             cls = get_writer(engine)
-        writer = cls.__new__(cls, path, **kwargs)
-        writer.__init__(path, **kwargs)
-        return writer
-
 
-@add_metaclass(ExcelWriterMeta)
-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.
+        return object.__new__(cls)
 
-    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.
-    """
     # 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"
@@ -407,9 +407,6 @@ def save(self):
         pass
 
     def __init__(self, path, engine=None, **engine_kwargs):
-        # note that subclasses will *never* get anything for engine
-        # included here so that it's visible as part of the public signature.
-
         # validate that this engine can handle the extnesion
         ext = os.path.splitext(path)[-1]
         self.check_extension(ext)
@@ -455,7 +452,7 @@ class _OpenpyxlWriter(ExcelWriter):
     engine = 'openpyxl'
     supported_extensions = ('.xlsx', '.xlsm')
 
-    def __init__(self, path, **engine_kwargs):
+    def __init__(self, path, engine=None, **engine_kwargs):
         # Use the openpyxl module as the Excel writer.
         from openpyxl.workbook import Workbook
 
@@ -511,6 +508,7 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
                                                startrow + cell.row + 1,
                                                cletterend,
                                                startrow + cell.mergestart + 1))
+
     @classmethod
     def _convert_to_style(cls, style_dict):
         """
@@ -539,7 +537,7 @@ class _XlwtWriter(ExcelWriter):
     engine = 'xlwt'
     supported_extensions = ('.xls',)
 
-    def __init__(self, path, **engine_kwargs):
+    def __init__(self, path, engine=None, **engine_kwargs):
         # Use the xlwt module as the Excel writer.
         import xlwt
 
@@ -599,7 +597,8 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
                           val, style)
 
     @classmethod
-    def _style_to_xlwt(cls, item, firstlevel=True, field_sep=',', line_sep=';'):
+    def _style_to_xlwt(cls, item, firstlevel=True, field_sep=',',
+                       line_sep=';'):
         """helper which recursively generate an xlwt easy style string
         for example:
 
@@ -617,12 +616,12 @@ def _style_to_xlwt(cls, item, firstlevel=True, field_sep=',', line_sep=';'):
         if hasattr(item, 'items'):
             if firstlevel:
                 it = ["%s: %s" % (key, cls._style_to_xlwt(value, False))
-                        for key, value in item.items()]
+                      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()]
+                      for key, value in item.items()]
                 out = "%s " % (field_sep).join(it)
                 return out
         else:
@@ -659,11 +658,11 @@ class _XlsxWriter(ExcelWriter):
     engine = 'xlsxwriter'
     supported_extensions = ('.xlsx',)
 
-    def __init__(self, path, **engine_kwargs):
+    def __init__(self, path, engine=None, **engine_kwargs):
         # Use the xlsxwriter module as the Excel writer.
         import xlsxwriter
 
-        super(_XlsxWriter, self).__init__(path, **engine_kwargs)
+        super(_XlsxWriter, self).__init__(path, engine=engine, **engine_kwargs)
 
         self.book = xlsxwriter.Workbook(path, **engine_kwargs)