Line indexing in Python

[r0g]

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


Cheers,


Roger.