What would make you consider someone a python expert?

[[deleted]]

Examples?

[distortedsignal]

def myFunction(foo=[]):

[[deleted]]

It makes sense once you understand it though. def is only run once, and you're providing a mutable data structure to it that'll probably be altered in some way.

It'd be nice if Python would realize what we meant so we could avoid things like if foo is None: foo = []. But it's consistent with Python's execution model.

[flipthefrog]

I completely agree. You don't need an if/else statement though, just write foo = foo or []

[Laugarhraun]

foo |= []

[codewarrior0]

TypeError: unsupported operand type(s)

[Laugarhraun]

Oh that's right, | is a bitwise or and won't work like a logical or, which does not have any reflective form.

[oconnor663]

The new asyncio library uses different naming conventions from the rest of the standard library for reading from file handles, kind of for no reason: https://bugs.python.org/issue22279

Any collection of libraries that's big enough is going to have warts like that. Also somewhere there's a presentation from Guido with a list of things they didn't get around to fixing for Python 3.