3.0: DateTime fields cannot be used as inner field for List or Tuple fields

Between releases 3.0.0rc8 and 3.0.0rc9, DateTime fields have started throwing an error when being instantiated as inner fields of container fields like List or Tuple. The snippet below works in <=3.0.0rc8 and throws the error below in >=3.0.0rc9 (and, worryingly, 3.0.0):

from marshmallow import fields, Schema

class MySchema(Schema):
    times = fields.List(fields.DateTime())

s = MySchema()

Traceback:

Traceback (most recent call last):
  File "test-mm.py", line 8, in <module>
    s = MySchema()
  File "/Users/victor/.pyenv/versions/marshmallow/lib/python3.6/site-packages/marshmallow/schema.py", line 383, in __init__
    self.fields = self._init_fields()
  File "/Users/victor/.pyenv/versions/marshmallow/lib/python3.6/site-packages/marshmallow/schema.py", line 913, in _init_fields
    self._bind_field(field_name, field_obj)
  File "/Users/victor/.pyenv/versions/marshmallow/lib/python3.6/site-packages/marshmallow/schema.py", line 969, in _bind_field
    field_obj._bind_to_schema(field_name, self)
  File "/Users/victor/.pyenv/versions/marshmallow/lib/python3.6/site-packages/marshmallow/fields.py", line 636, in _bind_to_schema
    self.inner._bind_to_schema(field_name, self)
  File "/Users/victor/.pyenv/versions/marshmallow/lib/python3.6/site-packages/marshmallow/fields.py", line 1117, in _bind_to_schema
    or getattr(schema.opts, self.SCHEMA_OPTS_VAR_NAME)
AttributeError: 'List' object has no attribute 'opts'

It seems like it’s treating the parent field as a Schema without checking that it is indeed a schema, so the schema.opts statement fails as fields don’t have an opts attribute.

[sloria]

Fix released in 3.0.1

[lafrech]

Let’s do that, then.

Not much time either. The first who gets the time can do it.

For the non-reg tests :

1/ a test that checks the format set in the schema is respected if the DateTime field is in a container field

2/ a set of tests asserting the _bind_to_schema method of inner fields List, Dict, Tuple is called from container fields (we can use DateTime with the same test case for that)

Perhaps 1/ is useless if 2/ is done.