Commonly-used names in the Python standard library

Chris Angelico rosuav at
Thu Feb 20 11:43:59 CET 2014

On Thu, Feb 20, 2014 at 9:22 PM, Marko Rauhamaa <marko at> wrote:
>   from py35 import *
> That way, you could choose between:
>   unless x > 7:
>       return
> and:
>   py35.unless x > 7:
>       return
> in case you have already made use of the name "unless" in your program.

What about return? Are you allowed to namespace that? And 'from' and
'import' and '*'?

In languages with keywords, they're there to signal things to the
parser. There are languages that have no keywords at all, like REXX,
and their grammars are usually restricted to non-alphabetic tokens
(for instance, REXX has & and | instead of "and" and "or"). Python
already has most of its important names in either builtins (which can
be shadowed) or actual modules, so it's only actual language keywords
that can't be reused; and there aren't all that many of those. But
more can be created, and it's worth being careful.

In this instance, various proposals included "then", "when", "use",
and "raises". My script reported the following:

1 instances of the name 'use'
12 instances of the name 'when'

and none of either of the others. Granted, the stdlib isn't
everything, and isn't even reliably representative, but that supported
my gut feeling that keywording 'when' would be likely to trip code up.

If you're curious about the full proposal, it's PEP 463, an expression
form of the 'except' statement. The latest draft PEP can be found

and the official repo (currently out of date, but later on will be the
official and maintained version) has it here:


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