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A common Python idiom is to test objects by value in an if. This includes container emptiness and regular expression matches, or using 'or' to specify a default value:
 if my_list:
 # list isn't empty
 if regex.match(string):
 # string matched the regex
 my_list = arg or [1,2,3]
It'd be nice if we could use this idiom with inspect.Signature._empty or inspect.Parameter.empty:
 sig = signature(func)
 for param in sig.parameters.values():
 if param.annotation:
 ...
or, to use a the example that motivated this idea:
 def arg_type(param):
 return param.annotation or str
The only issue I can think of is that, if an annotation or default value is some False value, like None, than the test will fail even if the value isn't _empty. However, this issue already exists for other uses of this idiom, and I think this is a perfect extension of the form.