ArgumentLoader is not able to handle type

[pengzhengyi]

Description

When retrieving type from field.type, type is a string literal indicating the type rather than the specific type class. Therefore, it cannot be added as type argument for add_argument in argparse as it expects a Callable.

Explanation

This issue arises because type evaluation is deferred when from __future__ import annotations is used.

For example,

• when import is not used

  class A:
    foo: str
  
  A.__annotatiions__
  # {'foo': <class 'str'>}

• when import is used

  from __future__ import annotations
  
  
  class A:
    foo: str
  
  A.__annotatiions__
  # {'foo': 'str'}

Therefore, if from __future__ import annotations is used at the module where the dataclass inheriting ArgumentLoader is used, it will cause field.type evaluates to string name of types like 'str', 'int' when deciding type during adding class field as an argument..

Workaround

A temporary workaround is avoiding using from __future__ import annotations when defining a class extending ArgumentLoader.