Validation check YD01 not implemented properly

[martinlackner]

Hello!

The validation check YD01 is not implemented properly. The specific code in validate.py is the following:

numpydoc/numpydoc/validate.py

Line 599 in f33a53e

if not doc.yields and "yield" in doc.method_source:

Since doc.method_source also contains the docstring, this condition is also satisfied if "yield" occurs in the docstring (where it might be used as a regular word).

I have encountered this bug in a function that did not contain a yield and it took me quite a while to figure out what was wrong.

[jnothman]

Also fires a false alarm when there is a generator nested within the function, or when a variable name includes "yield". Rather we should be using inspect.isgeneratorfunction