Issue 4575 ast get docstring return type

[mitch292]

Resolves #4575

get_docstring can return None in >= 3.6.

cc: @blueyed & @JelleZijlstra

[hauntsaninja]

Thanks! You'll want to address the CI lint failures.

Also the version check is incorrect, Python 3.5 returns None sometimes as well (it's just not as visible because the 3.5 source doesn't seem to be PEP8-compliant in this case). But you can demonstrate this empirically as well:

~ λ python3.5                                
Python 3.5.9 (default, Jun 11 2020, 19:03:06) 
[GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.32.62)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import ast
>>> mod = ast.parse("def f(): ...")
>>> mod.body
[<_ast.FunctionDef object at 0x1076dd080>]
>>> mod.body[0]
<_ast.FunctionDef object at 0x1076dd080>
>>> ast.get_docstring(mod.body[0])
>>> ast.get_docstring(mod.body[0]) is None
True

[hauntsaninja]

Please remove the version check :-) It's good the way you had it on your first commit

[hauntsaninja]

Thanks again!

[mitch292]

Thanks for the help @hauntsaninja !