Mutable default arguments are your friend.

In a recent comment to an elderly post of mine, I was asked about the following code:

def mywrapper(func, args=(), kwargs={}):
    ...

The commenter though that I should have made a special mention about using dict as a default argument, “because it’s such a common gotcha.”

My response is twofold:

  1. This particular case is idiomatic, and widely used for functions that call other functions.
  2. I actually don’t think mutable default arguments are a problem and that they don’t deserve all the stigma they are getting.

I want to expand on point 2 a bit here.

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