fields.py and corresponding tests have entered bloatware status

[hugocartwright]

I see numerous simple but possibly emotional issues for fields.py and test_fields.py which are both very large files. I would submit corresponding PRs as ideas the gist of which you can find below in no particular order:

1. Since fields.py and test_fields.py are very large they could possibly be split in some way. Parent and sub classes?

2. fields.py

• BuiltinSignatureError Exception not required and could be replaced with a standard TypeError / AttributeError / other but maybe keep the error message.

• CurrentUserDefault class could use a docstring and be reviewed together with the CreateOnlyDefault class

• Field class:

  • constructor could use some clarifying notably with keywords and their combinations
  • get_value and run_validators functions inexplicably complex and hard to read
  • get_attribute again the BuiltInSignature Exception as well as the rest of the function could be simplified

• BooleanField class: overly verbose and confusing, strtobool one of a couple of ideas

• DecimalField class: constructor is overly verbose possibly default_error_messages too

• CharField class: issues with constructor and run_validation function

• ListField class: overly confusing constructor

3. test_fields.py: multiple tests should be reviewed:

• TestIsSimpleCallable.test_method
• TestSource
  • test_source
  • test_redundant_source
  • test_callable_source
• TestBooleanField
• TestNullBooleanField
• TestNullableBooleanField
• TestRegexField
• TestiCompiledRegexField
• TestURLField
• TestUUIDField
• TestFilePathField
• TestIntegerField
• TestMinMaxIntegerField
• TestFloatField
• TestAllowNullDecimalField
• TestAllowNullNoStringCoercionDecimalField
• TestMinMaxDecimalField
• TestNoMaxDigitsDecimalField
• TestLocalizedDecimalField
• TestQuantizedValueForDecimal.test_int_quantized_value_for_decimal
• TestCustomOutputFormatDateField
• TestNoOutputFormatDateField
• TestDateTimeField
• TestNoOutputFormatTimeField
• TestDurationField
• TestChoiceField.test_allow_blank
• TestChoiceFieldWithType
• TestChoiceFieldWithGroupedChoices
• TestChoiceFieldWithMixedChoices
• TestEmptyMultipleChoiceField
• MockFile
• TestValidImageField
• TestJSONField

[hugocartwright]

Could the last 3 classes of generics.py be simplified to the following? (passes all tests)

class RetrieveUpdateAPIView(RetrieveAPIView, UpdateAPIView):
    """
    Concrete view for retrieving, updating a model instance.
    """
    pass


class RetrieveDestroyAPIView(RetrieveAPIView, DestroyAPIView):
    """
    Concrete view for retrieving or deleting a model instance.
    """
    pass


class RetrieveUpdateDestroyAPIView(RetrieveAPIView, UpdateAPIView, DestroyAPIView):
    """
    Concrete view for retrieving, updating or deleting a model instance.
    """
    pass