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Standing In Line - Python

Now that you know how to create and use Python's tuples, listsand dictionaries, it's time to get your hands dirty. In this article, findout how to read from, and write to, files on the filesystem with built-inPython methods, and also take a look at some of the new features availablein Python 2.x.

TABLE OF CONTENTS:
  1. Python 101 (part 5): Snake Oil For The Soul
  2. Air In A Bottle
  3. Treading The Right Path
  4. Standing In Line
  5. Learning To Write
  6. Desperately Seeking Python
  7. String Theory
  8. Pop() Goes The Weasel
By: Vikram Vaswani, (c) Melonfire
Rating: starstarstarstarstar / 4
July 09, 2001

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There's also another method of reading data from a file - the readline()method call, used to read a single line at a time.

>>> data = open("snakeoil.txt") >>> data.readline() 'After years of research, scientists at AB Labs have come up with a radical new product, once that promises to improve the quality of life for humans and animals everywhere.\012' >>> data.readline() ' \012' >>> data.readline() 'We call it Air In A Bottle(tm), and we firmly consider it to be one of our best inventions ever.\012' >>>
You can combine this with a loop that will run through the file, printingone line after another:

#!/usr/bin/python # open file data = open("snakeoil.txt") # read first line line = data.readline() # loop until EOF while line != "": print line, line = data.readline() else: print "-- all done --" # clean up data.close()
Well, it works - but how about making it a little more efficient? Insteadof reading a file line by line, you can also suck the entire thing straightinto your program via a list - definitely more likely to impress the girls!

#!/usr/bin/python # open file data = open("snakeoil.txt") # read file into list lines = data.readlines() # loop until EOF for x in lines: print x, else: print "-- all done --" # clean up data.close()
In this case, the readlines() method is used to read the file into a list.Each element of the list now corresponds to a single line from the file.

>>> data.readlines() ['After years of research, scientists at AB Labs have come up with a radical new product, once that promises to improve the quality of life for humans and animals everywhere.\012', ' \012', 'We call it Air In A Bottle(tm), and we firmly consider it to be one of our best inventions ever.\012', '\012', 'Carry it around with you (the bottle is titanium, the same material used in rocket ships, and the air is, well, air) and inhale from it whenever you need some air. Or give it to your friends as a present (after all, they need air too!)\012', '\012', 'Air In A Bottle(tm). Get some today!\012'] >>>
Once this has been done, it's a simple matter to run through the list anddisplay its contents with the "for" loop.

 
 
>>> More Python Articles          >>> More By Vikram Vaswani, (c) Melonfire
 

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