Use %prep from FPG/Python[1] example

  [1]: https://fedoraproject.org/wiki/Packaging:Python#Example_common_spec_file

ydiff.spec.in

 Python library that implements API used by ydiff tool.
 
 %prep
-%setup -q
+%autosetup -n %{name}-%{version}
 
 %build
 %py2_build