Function fields break with Python 3 type annotations

Let’s take the following simple test case:

from marshmallow import fields, Schema

def get_split_words(value: str):
    return value.split(';')

class TestSchema(Schema):
    name = fields.String(required=True)
    friends = fields.Function(serialize=None, deserialize=get_split_words)

data = {'name': 'Bruce Wayne', 'friends': 'Clark;Alfred;Robin'}
result = TestSchema().load(data)

That results in an error:

Traceback (most recent call last):
  File "mmtest.py", line 14, in <module>
    result = TestSchema().load(data)
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\schema.py", line 542, in load
    result, errors = self._do_load(data, many, partial=partial, postprocess=True)
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\schema.py", line 610, in _do_load
    index_errors=self.opts.index_errors,
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\marshalling.py", line 294, in deserialize
    index=(index if index_errors else None)
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\marshalling.py", line 67, in call_and_store
    value = getter_func(data)
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\marshalling.py", line 287, in <lambda>
    data
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\fields.py", line 263, in deserialize
    output = self._deserialize(value, attr, data)
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\fields.py", line 1199, in _deserialize
    return self._call_or_raise(self.deserialize_func, value, attr)
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\fields.py", line 1203, in _call_or_raise
    if len(utils.get_func_args(func)) > 1:
  File "C:\tools\py35-venv\lib\site-packages\marshmallow\utils.py", line 344, in get_func_args
    return inspect.getargspec(func).args
  File "C:\tools\Python35-32\lib\inspect.py", line 1045, in getargspec
    raise ValueError("Function has keyword-only arguments or annotations"
ValueError: Function has keyword-only arguments or annotations, use getfullargspec() API which can support them

The reason is: The marshmallow.utils module uses Python’s inspect.getargspec for inspecting the functions used in Function fields. However, getargspec is deprecated since Python 3.0 (https://docs.python.org/3/library/inspect.html#inspect.getargspec) and throws a ValueError when called on a function with type annotations.

The error message suggests to use getfullargspec instead, but that has been deprecated since version 3.5, too (https://docs.python.org/3/library/inspect.html#inspect.getfullargspec). So the most future-proof way is probably to use inspect.signature instead (https://docs.python.org/3/library/inspect.html#inspect.signature).

[sabinem]

I would like to work on this, if that’s okay with the community. I am a Newbie with contributing, so tell me if I am doing anything the wrong way. But I have been told that you should announce if you want to work on something. This seems like a bug and should be not too hard to fix.

[sloria]

This is now fixed in the latest PyPI release (2.10.4).