None in string => TypeError?

Newsgroups	comp.lang.python
Date	2014-06-09 08:34 -0700
Message-ID	<048960da-c132-407f-b1b3-4612a3dd7697@googlegroups.com> (permalink)
Subject	None in string => TypeError?
From	Roy Smith <roy@panix.com>

Show all headers | View raw

We noticed recently that:

>>> None in 'foo'

raises (at least in Python 2.7)

TypeError: 'in <string>' requires string as left operand, not NoneType

This is surprising.  The description of the 'in' operatator is, 'True if an item of s is equal to x, else False	'.  From that, I would assume it behaves as if it were written:

for item in iterable:
    if item == x:
        return True
else:
    return False

why the extra type check for str.__contains__()?  That seems very unpythonic.  Duck typing, and all that.

Back to comp.lang.python | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

None in string => TypeError? Roy Smith <roy@panix.com> - 2014-06-09 08:34 -0700
  Re: None in string => TypeError? Ryan Hiebert <ryan@ryanhiebert.com> - 2014-06-09 10:42 -0500
  Re: None in string => TypeError? Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-09 09:50 -0600
  Re: None in string => TypeError? Paul Sokolovsky <pmiscml@gmail.com> - 2014-06-09 18:57 +0300
    Re: None in string => TypeError? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 16:14 +0000
      Re: None in string => TypeError? Chris Angelico <rosuav@gmail.com> - 2014-06-10 02:31 +1000
  Re: None in string => TypeError? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 16:07 +0000
  Re: None in string => TypeError? MRAB <python@mrabarnett.plus.com> - 2014-06-09 17:06 +0100
  Re: None in string => TypeError? Shiyao Ma <i@introo.me> - 2014-06-10 00:13 +0800
  Re: None in string => TypeError? Roy Smith <roy@panix.com> - 2014-06-09 12:53 -0400
  Re: None in string => TypeError? Chris Angelico <rosuav@gmail.com> - 2014-06-10 02:59 +1000
  Re: None in string => TypeError? Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-09 11:22 -0600
  Re: None in string => TypeError? Chris Angelico <rosuav@gmail.com> - 2014-06-10 03:40 +1000
  Re: None in string => TypeError? Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-09 11:58 -0600
  Re: None in string => TypeError? Chris Angelico <rosuav@gmail.com> - 2014-06-10 04:02 +1000

csiph-web