what does `a: b` statement do in python?

Asked Jul 10 '19 at 17:01

Active Jul 10 '19 at 17:01

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I was modifying a dictionary, and accidentally wrote something like

data = dict(a=1, b=2)
if condition:
    data['c']: 3

I expected this to be a syntax error, however it runs correctly, and the statement simply seems to have no effect.

Which makes me curious: what kind of statement is this, and why is this legal?

asked Jul 10 '19 at 17:01

blue_note

They're called type annotations. https://www.python.org/dev/peps/pep-0526/#specification – abdusco Jul 10 '19 at 17:06
I get a syntax error at the colon symbol when I execute it. – Gilles-Philippe Paillé Jul 10 '19 at 17:07
@roganjosh: thanks, this seems to be it. – blue_note Jul 10 '19 at 17:07
@Gilles-PhilippePaillé presumably you have a version of Python < 3.6 – roganjosh Jul 10 '19 at 17:07
@Gilles-PhilippePaillé: I'm on python 3.6 – blue_note Jul 10 '19 at 17:07
@blue_note FWIW "python dictionary assignment by colon" in Google was what I searched to get that, and I wasn't immediately aware of the answer from the question – roganjosh Jul 10 '19 at 17:09

0 Answers0