[Tutor] Line in a file

[Erik Price]

On Thursday, July 18, 2002, at 06:33  PM, Michael Montagne wrote:

> How do I go directly to an exact line number in a file?

Well, I was trying to figure this one out for ya as an exercise, but I 
got stumped.  So in trying answer one question, another came up.  Can 
anyone tell me what's wrong here?

 >>> f = open('./sampletext.txt')			# open a file
 >>> line = f.readline()					# read a line
 >>> line								# print it
'this is line 1\n'
 >>> line2 = f.readline()				# read another line relative
 >>> line2								# to where we left off, print it
'this is line 2\n'
 >>> f.tell()							# what position are we at?
30L
 >>> f.seek(0)							# go back to the beginning of f
 >>> f.tell()							# make sure we're at the beginning
0L
 >>> i                       			# we set i to 0 earlier
0
 >>> for line in f.xreadlines():			# xreadlines() sequentially reads
...   i = i + 1						# lines, so this is one way to get
...   if (i == 3):						# a certain line from a file
...     print line						# (in this case line 3)
...
line 3 is high as my knee

 >>> f.tell()							# where are we now?
86L
 >>> f.seek(0)							# go back to the beginning of f
 >>> f.tell()							# double check
0L
 >>> def printLine(fh, num):				# let's make code reuseable
...   c = 0
...   for line in fh.xreadlines():
...     c = c + 1
...     if (line == num):
...       fh.seek(0)					# resets file pointer
...       return line					# returns the line we want
...
 >>> data = ''							# initialize a container variable
 >>> data = printLine(f, 2)				# try out our function
 >>> data								# nothing in the container!
 >>> print data						# nothing!
None
 >>>

Why doesn't this work?


Erik