Fix make_signature TypeError in py3 (#17609)

Author: jbrockmendel

pandas/tests/util/test_util.py

@@ -9,7 +9,7 @@
 import pytest
 from pandas.compat import intern
 from pandas.util._move import move_into_mutable_buffer, BadMove, stolenbuf
-from pandas.util._decorators import deprecate_kwarg
 from pandas.util._validators import (validate_args, validate_kwargs,
                                      validate_args_and_kwargs,
                                      validate_bool_kwarg)
@@ -467,3 +467,17 @@ def test_set_locale(self):
 
         current_locale = locale.getlocale()
         assert current_locale == self.current_locale
+
+
+def test_make_signature():
+    # See GH 17608
+    # Case where the func does not have default kwargs
+    sig = make_signature(validate_kwargs)
+    assert sig == (['fname', 'kwargs', 'compat_args'],
+                   ['fname', 'kwargs', 'compat_args'])
+
+    # Case where the func does have default kwargs
+    sig = make_signature(deprecate_kwarg)
+    assert sig == (['old_arg_name', 'new_arg_name',
+                    'mapping=None', 'stacklevel=2'],
+                   ['old_arg_name', 'new_arg_name', 'mapping', 'stacklevel'])

pandas/util/_decorators.py

@@ -242,7 +242,7 @@ def make_signature(func):
         defaults = ('',) * n_wo_defaults
     else:
         n_wo_defaults = len(spec.args) - len(spec.defaults)
-        defaults = ('',) * n_wo_defaults + spec.defaults
     args = []
     for i, (var, default) in enumerate(zip(spec.args, defaults)):
         args.append(var if default == '' else var + '=' + repr(default))