Python: catching mutable default arguments

I know about the problem and how to fix it. I would like to ask for help finding this problem in existing code.

In other words, I'm trying to find all loc开发者_如何学Pythonations where this trap is buried, so I can fix it.

Is there any tool that can help me?

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Pylint has a warning for default argument values of mutable types. It's customizable, so you could get it to just do this if you wanted.

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What's wrong with grep?

grep "^\s*def.*=(\[\]|\{\}|set\(\))"

This will find just about all of the usual culprits.

If you're using a instance of one of your own mutable classes as a default value, you'll have to check for that separately.

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The regex proposed by @S.Lott is also finding function/method calls, but we just want to find function/method definitions.

So here is an updated version of the regex to find the location of all function/method signatures which uses mutable default argument:

def .+?\([^:]*?(=\[\]|=\{\}|set\(\))[^:]*?\):

Note:

if you are using PyCharm, it will add a yellowish background to these arguments and help you change the code.

Enjoy!