Use DeprecationWarning for core.common deprecations (GH13634)

Related to second question in #13634 (whether to use FutureWarning or
DeprecationWarning in deprecating the public pandas.core.common
functions).    As those functions are mostly used in library code, and
less directly by users in their own code, I think a DeprecationWarning
is more appropriate in this case.   For example, in our own docs, we
started to get warnings due to an example with a statsmodels
regression that uses patsy using one of those functions. Note that
recent IPython also shows DeprecationWarnings when using a deprecated
function interactively.

Author: Joris Van den Bossche <[email protected]>

Closes #13990 from jorisvandenbossche/common-depr-warning and squashes the following commits:

2de5d48 [Joris Van den Bossche] Use DeprecationWarning for core.common deprecations (GH13634)

Author: jorisvandenbossche

doc/source/whatsnew/v0.19.0.txt

@@ -31,7 +31,7 @@ pandas development API
 As part of making pandas APi more uniform and accessible in the future, we have created a standard
 sub-package of pandas, ``pandas.api`` to hold public API's. We are starting by exposing type
 introspection functions in ``pandas.api.types``. More sub-packages and officially sanctioned API's
-will be published in future versions of pandas.
+will be published in future versions of pandas (:issue:`13147`, :issue:`13634`)
 
 The following are now part of this API:
 
@@ -42,6 +42,10 @@ The following are now part of this API:
    funcs = [ f for f in dir(types) if not f.startswith('_') ]
    pprint.pprint(funcs)
 
+.. note::
+
+   Calling these functions from the internal module ``pandas.core.common`` will now show a ``DeprecationWarning`` (:issue:`13990`)
+
 .. _whatsnew_0190.enhancements.asof_merge:
 
 ``merge_asof`` for asof-style time-series joining

pandas/api/tests/test_api.py

@@ -163,7 +163,7 @@ def test_types(self):
         self.check(types, self.allowed)
 
     def check_deprecation(self, fold, fnew):
-        with tm.assert_produces_warning(FutureWarning):
+        with tm.assert_produces_warning(DeprecationWarning):
             try:
                 result = fold('foo')
                 expected = fnew('foo')

pandas/core/common.py

@@ -31,7 +31,7 @@ def wrapper(*args, **kwargs):
             warnings.warn("pandas.core.common.{t} is deprecated. "
                           "import from the public API: "
                           "pandas.api.types.{t} instead".format(t=t),
-                          FutureWarning, stacklevel=3)
+                          DeprecationWarning, stacklevel=3)
             return getattr(types, t)(*args, **kwargs)
         return wrapper
 
@@ -57,7 +57,7 @@ def wrapper(*args, **kwargs):
                           "These are not longer public API functions, "
                           "but can be imported from "
                           "pandas.types.common.{t} instead".format(t=t),
-                          FutureWarning, stacklevel=3)
+                          DeprecationWarning, stacklevel=3)
             return getattr(common, t)(*args, **kwargs)
         return wrapper