__contains__ inconsistencies between Python 2.2 and 2.3

Steve Holden steve at holdenweb.com
Fri Mar 4 21:32:53 CET 2005


Anand S Bisen wrote:
> Hello
> 
> I have been developing a code that works pretty well on my python 2.3 
> and now when i am running it on my server where it is programmed to run 
> it's giving me errors. I have been using __contains__ method and it 
> fails on python 2.2
> 
> For example
> 
> (Python 2.3)
>  >> x="Hello World"
>  >> print x.__contains__("Hello")
> True
> 
> (Python 2.2)
> 
>  >>> x="Hello world"
>  >>> print x.__contains__("Hello")
> 
> Traceback (most recent call last):
>  File "<stdin>", line 1, in ?
> TypeError: 'in <string>' requires character as left operand
> 
> 
> Is there any woraround for this or what am i doing wrong in 2.2 ?
> 
> Thanks
> 
Any use of double-underscores is an indication that magic is at work. In 
this case the __contains__ method is intended to be called by the 
interpreter when you write

     x in s

The __contains__ method was extended for strings in 2.3 so that 
construct could be used as a test to see whether s contained x as a 
substring. Before that, as the error message explains, it will only test 
to see whether a single character is contained in the string (by analogy 
with

     1 in [3, 4, 5, 2]

in case you are interested).

So you'll need to use the .find() string method and say

     if x.find("Hello") != -1:
         ... you found "Hello"

because your ISP appears to be using an older version of Python than you.

regards
  Steve
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Steve Holden                           http://www.holdenweb.com/



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