docstrings, remove need for swapaxes

Author: jbrockmendel

pandas/core/arrays/base.py

@@ -1128,11 +1128,14 @@ class ReshapeMixin:
 
     Subclass must implement _wrap_data property.
 
-    NB: we assume that the constructor will accept:
-
+    Notes
+    -----
+    - We assume that the constructor will accept:
         type(self)(self._wrap_data.reshape(shape), dtype=self.dtype)
-
-    If not, then the methods below will need to be overriden.
+      If not, then the methods below will need to be overriden.
+    - We assume that the only 2D shapes taken will be (N, 1) and (1, N).
+      This ensures that we can reshape, transpose, and ravel without worrying
+      about column-order/row-order.
     """
 
     @property
@@ -1178,10 +1181,3 @@ def T(self):
     def ravel(self, order=None):
         data = self._wrap_data.ravel(order=order)
         return type(self)(data, dtype=self.dtype)
-
-    def swapaxes(self, axis1, axis2):  # TODO: needs test
-        data = self._wrap_data.swapaxes(axis1, axis2)
-        return type(self)(data, dtype=self.dtype)
-
-    # TODO: Squeeze
-    # TODO: comments about reshape/ravel order

pandas/core/arrays/datetimelike.py

@@ -539,7 +539,6 @@ def astype(self, dtype, copy=True):
         dtype = pandas_dtype(dtype)
 
         if is_object_dtype(dtype):
-            # TODO: Do we need to worry about order for ravel/reshape?
             return self._box_values(self.asi8.ravel()).reshape(self.shape)
         elif is_string_dtype(dtype) and not is_categorical_dtype(dtype):
             return self._format_native_types()

pandas/core/groupby/ops.py

@@ -476,9 +476,7 @@ def _cython_operation(self, kind, values, how, axis, min_count=-1,
             if axis > 0:
                 swapped = True
                 assert axis == 1, axis
-                # TODO: can we just use values.T here?
-                #  i.e. will axis ever by greater than 1?
-                values = values.swapaxes(0, axis)
+                values = values.T
             if arity > 1:
                 raise NotImplementedError("arity of more than 1 is not "
                                           "supported for the 'how' argument")

pandas/core/internals/blocks.py

@@ -744,7 +744,6 @@ def replace(self, to_replace, value, inplace=False, filter=None,
                 mask[filtered_out.nonzero()[0]] = False
 
             if not mask.any():
-                # TODO: is this the right copy semantics?
                 if convert:
                     # NB: this check must come before the "if inplace" check
                     out = self.convert(by_item=True, numeric=False,
@@ -804,7 +803,7 @@ def setitem(self, indexer, value):
             if self.is_numeric:
                 value = np.nan
 
-        # TODO: For each DatetimeTZBlock can we just call values__setitem__ directly?
+        # TODO: For DatetimeTZBlock can we call values.__setitem__ directly?
         # coerce if block dtype can store value
         values = self.values
         try:
@@ -1431,7 +1430,6 @@ def quantile(self, qs, interpolation='linear', axis=0):
             # but `Block.get_values()` returns an ndarray of objects
             # right now. We need an API for "values to do numeric-like ops on"
             values = self.values.asi8
-            # TODO: is the above still needed?
         else:
             values = self.get_values()
             values, _ = self._try_coerce_args(values, values)
@@ -3156,7 +3154,11 @@ def _block_shape(values, ndim=1, shape=None):
     if values.ndim < ndim:
         if shape is None:
             shape = values.shape
-        if not is_extension_array_dtype(values):
+        if isinstance(values, ABCDatetimeIndex):
+            # DatetimeArray can be reshaped; DatetimeIndex cannot
+            values = values._data
+        if (not is_extension_array_dtype(values)
+                or is_datetime64tz_dtype(values)):
             # TODO: https://github.com/pandas-dev/pandas/issues/23023
             # block.shape is incorrect for "2D" ExtensionArrays
             # We can't, and don't need to, reshape.