[Tutor] printing a word in the second line of a text file

[Jeff Shannon]

> tonycervone <tonycervone@netzero.net> asked:
>
> ... How about if I want  to print a
> word according to any location in the second line of  a text? ...
>
> and  Remco Gerlich <scarblac@pino.selwerd.nl> replied:

>
> inp.readlines() returns a list of lines. split() is something you can do on
> an individual line. So you're almost there.
>
> What you wanted is read a single line, the first one. that's readline, not
> readlines.
>
> inp = open('filename')
> line = inp.readline()
> print line.split()[position]
>
> If you want to use readlines, it's read
>
> inp = open('filename')
> lines = inp.readlines()
> print lines[0].split()[position]
>

Now, in order to read a word from the second line, or whatever line number you want... you can do this in one of two ways:

---- example 1 ------

lineno = 2 # this is the line you want to read a word from...

inp = open('filename')
for n in range(lineno):   #loop through this a number of times equal to lineno ...
    line = inp.readline()   # reading a single line (lineno times)
print line.split()[position]

---- example 2 ------

inp = open('filename')
lines = inp.readlines()   # read in the entire file
myline = lines[lineno - 1] # grab the line we're interested in
print myline.split()[position]

-----------------------

Note that in example 2, when I go to grab the line I want, I use (lineno - 1)--this is because lists use 0-based indexing, instead of the 1-based counting that humans normally use (and yes, there *are* good reasons for this, but I won't go into them here).  Example 1 uses a fairly slow loop-and-read process, while example 2 reads the entire file in one
gulp.  As a result, example 2 will be quicker and probably more efficient for small files, or files that you want to look near the *end* of.  Example 1 will be better for reading lines near the beginning of large files.  Of course, exactly what "small" and "large" means, will depend on your processor, available memory, disk, etc... ;)  (I'd use example 2
in strong preference to example 1, unless you're always grabbing from the first line or two, or are *very* short on memory... )

Jeff Shannon
Technician/Programmer
Credit International