None in string => TypeError?

[MRAB]

On 2014-06-09 16:34, Roy Smith wrote:
> 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.
>
When working with strings, it's not entirely the same. For example:

 >>> 'oo' in 'foo'
True

If you iterated over the string, it would return False.