How to use Generics?

[justuswilhelm]

In mypy you can use this

import typing


def returns_dict() -> typing.Mapping:
    return dict()


returns_dict()

And it validates just fine.

But with enforce I get a strange result

import enforce
import typing


@enforce.runtime_validation
def returns_dict() -> typing.Mapping:
    return dict


returns_dict()

Seemingly, the generic type handling is different in enforce.

Traceback (most recent call last):                
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/nodes.py", line 539, in preprocess_data
    enforcer = data.__enforcer__                  
AttributeError: type object 'dict' has no attribute '__enforcer__'                                   

During handling of the above exception, another exception occurred:                                  

Traceback (most recent call last):                
  File "test.py", line 10, in <module>            
    returns_dict()       
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/decorators.py", line 118, in universal
    return enforcer.validate_outputs(result)      
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/enforcers.py", line 96, in validate_outputs
    if not self.validator.validate(output_data, 'return'):                                           
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/validator.py", line 26, in validate
    validation_result = visit(validation_tree)    
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/utils.py", line 17, in visit
    stack.append(last.send(last_result))          
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/nodes.py", line 64, in validate
    clean_data = self.preprocess_data(validator, data)                                               
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/nodes.py", line 541, in preprocess_data
    return GenericProxy(data)                     
  File "/Users/XXX/enforce-test/env/lib/python3.6/site-packages/enforce/enforcers.py", line 130, in __init__
    raise TypeError('Only generics can be wrapped in GenericProxy')                                  
TypeError: Only generics can be wrapped in GenericProxy    

What's the best way to get a similar behavior to mypy?

[RussBaz]

Well, you are not returning a dictionary in your second example. The return value is a function which returns a dictionary. Is it a typo or is it what you intended?

[justuswilhelm]

Sorry, that was a typo in my post above. The method should return dict(). I tried return a dict type just now, and that does not change the error message. Which makes sense, since the decorator phase fails, not the execution phase.