Line indexing in Python

Steve Holden steve at holdenweb.com
Tue Dec 22 13:25:51 CET 2009


r0g wrote:
> seafoid wrote:
>> Hi Guys,
>>
>> When python reads in a file, can lines be referred to via an index?
>>
>> Example:
>>
>> for line in file:
>>      if line[0] == '0':
>>          a.write(line)
>>
>> This works, however, I am unsure if line[0] refers only to the first line or
>> the first character in all lines.
>>
>> Is there an easy way to refer to a line with the first character being a
>> single letter that you know?
>>
>> Thanks in advance,
>> Seafoid.
> 
> 
> If you want to know the index number of an item in a sequence you are
> looping through (whether it be a file of lines or a list of characters,
> whatever) use enumerate...
> 
>>>> for index, value in enumerate("ABCD"):
>         print index, value
> ...
> 0 A
> 1 B
> 2 C
> 3 D
> 
> 
> If you want to extract an index number from the first part of of a given
> line use split( split_character, maximum_splits_to_do ) and then angle
> brackets to reference the first part (index 0)...
> 
> 
>>>> a = "20 GOTO 10"
>>>> int( a.split(' ',1)[0] )
> 20
> 
<nit>
those are brackets, not angle brackets
</nit>

regards
 Steve
-- 
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