Why context=None ?

Question

My question is bit *pythonic*. but I am curious to know the answer.
I have seen in method Odoo is passing context=None. like
def create(self, cr, uid, vals, context=None):
if not context: context = {}
'''
code
'''  Why they have not used context={}? like
def create(self, cr, uid, vals, context={}):
'''
code
'''  can anyone shade light on it?

NUMERIGRAPHE · Answer

Because {} is mutable and None is immutable.
Mutable default values are awkward: if you change the value in you function it will also change the *default* value for all later calls of your function.
See https://doc.odoo.com/contribute/15_guidelines/coding_guidelines_framework/#the-infamous-context
The lengthy discussion about that here: https://bugs.launchpad.net/openobject-addons/+bug/525808

Ludovic CHEVALIER · Answer

This notation in python mean that context is a optionnal arg of the function. If no context is given, context is equal to none.

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