Unrelated cleanups of source.py
Unrelated cleanups of source.py

nicoddemus/pytest,alfredodeza/pytest,hackebrot/pytest,markshao/pytest,Akasurde/pytest,The-Compiler/pytest,pytest-dev/pytest,txomon/pytest,RonnyPfannschmidt/pytest,The-Compiler/pytest,nicoddemus/pytest,tomviner/pytest,tomviner/pytest,pfctdayelise/pytest