Fix docstring of functions created with the deprecate() function (pandas-dev#24215)

* Fix docstring of functions created with the deprecate() function

* Allowing deprecate to be used with functions without docstring

Author: datapythonista

pandas/tests/util/test_deprecate.py

@@ -0,0 +1,63 @@
+from textwrap import dedent
+
+import pytest
+
+from pandas.util._decorators import deprecate
+
+import pandas.util.testing as tm
+
+
+def new_func():
+    """
+    This is the summary. The deprecate directive goes next.
+
+    This is the extended summary. The deprecate directive goes before this.
+    """
+    return 'new_func called'
+
+
+def new_func_no_docstring():
+    return 'new_func_no_docstring called'
+
+
+def new_func_wrong_docstring():
+    """Summary should be in the next line."""
+    return 'new_func_wrong_docstring called'
+
+
+def new_func_with_deprecation():
+    """
+    This is the summary. The deprecate directive goes next.
+
+    .. deprecated:: 1.0
+        Use new_func instead.
+
+    This is the extended summary. The deprecate directive goes before this.
+    """
+    pass
+
+
+def test_deprecate_ok():
+    depr_func = deprecate('depr_func', new_func, '1.0',
+                          msg='Use new_func instead.')
+
+    with tm.assert_produces_warning(FutureWarning):
+        result = depr_func()
+
+    assert result == 'new_func called'
+    assert depr_func.__doc__ == dedent(new_func_with_deprecation.__doc__)
+
+
+def test_deprecate_no_docstring():
+    depr_func = deprecate('depr_func', new_func_no_docstring, '1.0',
+                          msg='Use new_func instead.')
+    with tm.assert_produces_warning(FutureWarning):
+        result = depr_func()
+    assert result == 'new_func_no_docstring called'
+
+
+def test_deprecate_wrong_docstring():
+    with pytest.raises(AssertionError, match='deprecate needs a correctly '
+                                             'formatted docstring'):
+        deprecate('depr_func', new_func_wrong_docstring, '1.0',
+                  msg='Use new_func instead.')

pandas/util/_decorators.py

@@ -1,6 +1,6 @@
-from functools import WRAPPER_ASSIGNMENTS, update_wrapper, wraps
+from functools import wraps
 import inspect
-from textwrap import dedent, wrap
+from textwrap import dedent
 import warnings
 
 from pandas._libs.properties import cache_readonly  # noqa
@@ -39,26 +39,37 @@ def deprecate(name, alternative, version, alt_name=None,
     warning_msg = msg or '{} is deprecated, use {} instead'.format(name,
                                                                    alt_name)
 
-    # adding deprecated directive to the docstring
-    msg = msg or 'Use `{alt_name}` instead.'.format(alt_name=alt_name)
-    msg = '\n    '.join(wrap(msg, 70))
-
-    @Substitution(version=version, msg=msg)
-    @Appender(alternative.__doc__)
+    @wraps(alternative)
     def wrapper(*args, **kwargs):
-        """
-        .. deprecated:: %(version)s
-
-           %(msg)s
-
-        """
         warnings.warn(warning_msg, klass, stacklevel=stacklevel)
         return alternative(*args, **kwargs)
 
-    # Since we are using Substitution to create the required docstring,
-    # remove that from the attributes that should be assigned to the wrapper
-    assignments = tuple(x for x in WRAPPER_ASSIGNMENTS if x != '__doc__')
-    update_wrapper(wrapper, alternative, assigned=assignments)
+    # adding deprecated directive to the docstring
+    msg = msg or 'Use `{alt_name}` instead.'.format(alt_name=alt_name)
+    doc_error_msg = ('deprecate needs a correctly formatted docstring in '
+                     'the target function (should have a one liner short '
+                     'summary, and opening quotes should be in their own '
+                     'line). Found:\n{}'.format(alternative.__doc__))
+
+    # when python is running in optimized mode (i.e. `-OO`), docstrings are
+    # removed, so we check that a docstring with correct formatting is used
+    # but we allow empty docstrings
+    if alternative.__doc__:
+        if alternative.__doc__.count('\n') < 3:
+            raise AssertionError(doc_error_msg)
+        empty1, summary, empty2, doc = alternative.__doc__.split('\n', 3)
+        if empty1 or empty2 and not summary:
+            raise AssertionError(doc_error_msg)
+        wrapper.__doc__ = dedent("""
+        {summary}
+
+        .. deprecated:: {depr_version}
+            {depr_msg}
+
+        {rest_of_docstring}""").format(summary=summary.strip(),
+                                       depr_version=version,
+                                       depr_msg=msg,
+                                       rest_of_docstring=dedent(doc))
 
     return wrapper