REF: separate to_time, avoid runtime imports (#34145)

Author: jbrockmendel

pandas/core/indexes/datetimelike.py

@@ -8,6 +8,7 @@
 
 from pandas._libs import NaT, Timedelta, iNaT, join as libjoin, lib
 from pandas._libs.tslibs import timezones
+from pandas._libs.tslibs.parsing import DateParseError
 from pandas._typing import Label
 from pandas.compat.numpy import function as nv
 from pandas.errors import AbstractMethodError
@@ -41,7 +42,6 @@
 from pandas.core.indexes.numeric import Int64Index
 from pandas.core.ops import get_op_result_name
 from pandas.core.sorting import ensure_key_mapped
-from pandas.core.tools.datetimes import DateParseError
 from pandas.core.tools.timedeltas import to_timedelta
 
 from pandas.tseries.offsets import DateOffset, Tick

pandas/core/indexes/datetimes.py

@@ -27,7 +27,7 @@
 from pandas.core.indexes.base import Index, InvalidIndexError, maybe_extract_name
 from pandas.core.indexes.datetimelike import DatetimeTimedeltaMixin
 from pandas.core.indexes.extension import inherit_names
-import pandas.core.tools.datetimes as tools
+from pandas.core.tools.times import to_time
 
 from pandas.tseries.frequencies import to_offset
 from pandas.tseries.offsets import prefix_mapping
@@ -778,8 +778,8 @@ def indexer_between_time(
         indexer_at_time : Get index locations of values at particular time of day.
         DataFrame.between_time : Select values between particular times of day.
         """
-        start_time = tools.to_time(start_time)
-        end_time = tools.to_time(end_time)
+        start_time = to_time(start_time)
+        end_time = to_time(end_time)
         time_micros = self._get_time_micros()
         start_micros = _time_to_micros(start_time)
         end_micros = _time_to_micros(end_time)

pandas/core/indexes/period.py

@@ -7,7 +7,7 @@
 from pandas._libs.lib import no_default
 from pandas._libs.tslibs import Period
 from pandas._libs.tslibs.frequencies import get_freq_group
-from pandas._libs.tslibs.parsing import parse_time_string
+from pandas._libs.tslibs.parsing import DateParseError, parse_time_string
 from pandas._typing import DtypeObj, Label
 from pandas.util._decorators import Appender, cache_readonly, doc
 
@@ -43,7 +43,6 @@
 from pandas.core.indexes.extension import inherit_names
 from pandas.core.indexes.numeric import Int64Index
 from pandas.core.ops import get_op_result_name
-from pandas.core.tools.datetimes import DateParseError
 
 from pandas.tseries.offsets import DateOffset, Tick
 

pandas/core/tools/datetimes.py

@@ -1,8 +1,9 @@
 from collections import abc
-from datetime import datetime, time
+from datetime import datetime
 from functools import partial
 from itertools import islice
-from typing import List, Optional, TypeVar, Union
+from typing import TYPE_CHECKING, Optional, TypeVar, Union
+import warnings
 
 import numpy as np
 
@@ -28,28 +29,31 @@
     is_numeric_dtype,
     is_scalar,
 )
-from pandas.core.dtypes.generic import (
-    ABCDataFrame,
-    ABCDatetimeIndex,
-    ABCIndex,
-    ABCIndexClass,
-    ABCSeries,
-)
+from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
 from pandas.core.dtypes.missing import notna
 
 from pandas.arrays import DatetimeArray, IntegerArray
 from pandas.core import algorithms
 from pandas.core.algorithms import unique
-from pandas.core.arrays.datetimes import tz_to_dtype
+from pandas.core.arrays.datetimes import (
+    maybe_convert_dtype,
+    objects_to_datetime64ns,
+    tz_to_dtype,
+)
+from pandas.core.indexes.base import Index
+from pandas.core.indexes.datetimes import DatetimeIndex
+
+if TYPE_CHECKING:
+    from pandas import Series  # noqa:F401
 
 # ---------------------------------------------------------------------
 # types used in annotations
 
-ArrayConvertible = Union[list, tuple, ArrayLike, ABCSeries]
+ArrayConvertible = Union[list, tuple, ArrayLike, "Series"]
 Scalar = Union[int, float, str]
 DatetimeScalar = TypeVar("DatetimeScalar", Scalar, datetime)
 DatetimeScalarOrArrayConvertible = Union[
-    DatetimeScalar, list, tuple, ArrayLike, ABCSeries
+    DatetimeScalar, list, tuple, ArrayLike, "Series"
 ]
 
 
@@ -156,7 +160,7 @@ def _maybe_cache(arg, format, cache, convert_listlike):
 
 def _box_as_indexlike(
     dt_array: ArrayLike, utc: Optional[bool] = None, name: Optional[str] = None
-) -> Union[ABCIndex, ABCDatetimeIndex]:
+) -> Index:
     """
     Properly boxes the ndarray of datetimes to DatetimeIndex
     if it is possible or to generic Index instead
@@ -176,7 +180,6 @@ def _box_as_indexlike(
         - DatetimeIndex if convertible to sole datetime64 type
         - general Index otherwise
     """
-    from pandas import DatetimeIndex, Index
 
     if is_datetime64_dtype(dt_array):
         tz = "utc" if utc else None
@@ -186,9 +189,9 @@ def _box_as_indexlike(
 
 def _convert_and_box_cache(
     arg: DatetimeScalarOrArrayConvertible,
-    cache_array: ABCSeries,
+    cache_array: "Series",
     name: Optional[str] = None,
-) -> ABCIndexClass:
+) -> "Index":
     """
     Convert array of dates with a cache and wrap the result in an Index.
 
@@ -235,7 +238,6 @@ def _return_parsed_timezone_results(result, timezones, tz, name):
     if tz is not None:
         # Convert to the same tz
         tz_results = np.array([tz_result.tz_convert(tz) for tz_result in tz_results])
-    from pandas import Index
 
     return Index(tz_results, name=name)
 
@@ -281,11 +283,6 @@ def _convert_listlike_datetimes(
     -------
     Index-like of parsed dates
     """
-    from pandas import DatetimeIndex
-    from pandas.core.arrays.datetimes import (
-        maybe_convert_dtype,
-        objects_to_datetime64ns,
-    )
 
     if isinstance(arg, (list, tuple)):
         arg = np.array(arg, dtype="O")
@@ -332,7 +329,6 @@ def _convert_listlike_datetimes(
             )
 
         if errors == "ignore":
-            from pandas import Index
 
             result = Index(result, name=name)
         else:
@@ -366,8 +362,6 @@ def _convert_listlike_datetimes(
             result = np.array(["NaT"], dtype="datetime64[ns]").repeat(len(arg))
             return DatetimeIndex(result, name=name)
         elif errors == "ignore":
-            from pandas import Index
-
             result = Index(arg, name=name)
             return result
         raise
@@ -539,9 +533,7 @@ def _adjust_to_origin(arg, origin, unit):
         offset = offset // tslibs.Timedelta(1, unit=unit)
 
         # scalars & ndarray-like can handle the addition
-        if is_list_like(arg) and not isinstance(
-            arg, (ABCSeries, ABCIndexClass, np.ndarray)
-        ):
+        if is_list_like(arg) and not isinstance(arg, (ABCSeries, Index, np.ndarray)):
             arg = np.asarray(arg)
         arg = arg + offset
     return arg
@@ -749,7 +741,7 @@ def to_datetime(
             result = arg._constructor(values, index=arg.index, name=arg.name)
     elif isinstance(arg, (ABCDataFrame, abc.MutableMapping)):
         result = _assemble_from_unit_mappings(arg, errors, tz)
-    elif isinstance(arg, ABCIndexClass):
+    elif isinstance(arg, Index):
         cache_array = _maybe_cache(arg, format, cache, convert_listlike)
         if not cache_array.empty:
             result = _convert_and_box_cache(arg, cache_array, name=arg.name)
@@ -944,131 +936,14 @@ def calc_with_mask(carg, mask):
     return None
 
 
-# Fixed time formats for time parsing
-_time_formats = [
-    "%H:%M",
-    "%H%M",
-    "%I:%M%p",
-    "%I%M%p",
-    "%H:%M:%S",
-    "%H%M%S",
-    "%I:%M:%S%p",
-    "%I%M%S%p",
-]
-
-
-def _guess_time_format_for_array(arr):
-    # Try to guess the format based on the first non-NaN element
-    non_nan_elements = notna(arr).nonzero()[0]
-    if len(non_nan_elements):
-        element = arr[non_nan_elements[0]]
-        for time_format in _time_formats:
-            try:
-                datetime.strptime(element, time_format)
-                return time_format
-            except ValueError:
-                pass
-
-    return None
-
-
 def to_time(arg, format=None, infer_time_format=False, errors="raise"):
-    """
-    Parse time strings to time objects using fixed strptime formats ("%H:%M",
-    "%H%M", "%I:%M%p", "%I%M%p", "%H:%M:%S", "%H%M%S", "%I:%M:%S%p",
-    "%I%M%S%p")
-
-    Use infer_time_format if all the strings are in the same format to speed
-    up conversion.
-
-    Parameters
-    ----------
-    arg : string in time format, datetime.time, list, tuple, 1-d array,  Series
-    format : str, default None
-        Format used to convert arg into a time object.  If None, fixed formats
-        are used.
-    infer_time_format: bool, default False
-        Infer the time format based on the first non-NaN element.  If all
-        strings are in the same format, this will speed up conversion.
-    errors : {'ignore', 'raise', 'coerce'}, default 'raise'
-        - If 'raise', then invalid parsing will raise an exception
-        - If 'coerce', then invalid parsing will be set as None
-        - If 'ignore', then invalid parsing will return the input
-
-    Returns
-    -------
-    datetime.time
-    """
-
-    def _convert_listlike(arg, format):
-
-        if isinstance(arg, (list, tuple)):
-            arg = np.array(arg, dtype="O")
-
-        elif getattr(arg, "ndim", 1) > 1:
-            raise TypeError(
-                "arg must be a string, datetime, list, tuple, 1-d array, or Series"
-            )
-
-        arg = ensure_object(arg)
-
-        if infer_time_format and format is None:
-            format = _guess_time_format_for_array(arg)
-
-        times: List[Optional[time]] = []
-        if format is not None:
-            for element in arg:
-                try:
-                    times.append(datetime.strptime(element, format).time())
-                except (ValueError, TypeError) as err:
-                    if errors == "raise":
-                        msg = (
-                            f"Cannot convert {element} to a time with given "
-                            f"format {format}"
-                        )
-                        raise ValueError(msg) from err
-                    elif errors == "ignore":
-                        return arg
-                    else:
-                        times.append(None)
-        else:
-            formats = _time_formats[:]
-            format_found = False
-            for element in arg:
-                time_object = None
-                for time_format in formats:
-                    try:
-                        time_object = datetime.strptime(element, time_format).time()
-                        if not format_found:
-                            # Put the found format in front
-                            fmt = formats.pop(formats.index(time_format))
-                            formats.insert(0, fmt)
-                            format_found = True
-                        break
-                    except (ValueError, TypeError):
-                        continue
-
-                if time_object is not None:
-                    times.append(time_object)
-                elif errors == "raise":
-                    raise ValueError(f"Cannot convert arg {arg} to a time")
-                elif errors == "ignore":
-                    return arg
-                else:
-                    times.append(None)
-
-        return times
-
-    if arg is None:
-        return arg
-    elif isinstance(arg, time):
-        return arg
-    elif isinstance(arg, ABCSeries):
-        values = _convert_listlike(arg._values, format)
-        return arg._constructor(values, index=arg.index, name=arg.name)
-    elif isinstance(arg, ABCIndexClass):
-        return _convert_listlike(arg, format)
-    elif is_list_like(arg):
-        return _convert_listlike(arg, format)
+    # GH#34145
+    warnings.warn(
+        "`to_time` has been moved, should be imported from pandas.core.tools.times.  "
+        "This alias will be removed in a future version.",
+        FutureWarning,
+        stacklevel=2,
+    )
+    from pandas.core.tools.times import to_time
 
-    return _convert_listlike(np.array([arg]), format)[0]
+    return to_time(arg, format, infer_time_format, errors)