[perl-python] 20050121 file reading & writing

From: Xah Lee (xah_at_xahlee.org)
Date: 01/22/05 

Date: 22 Jan 2005 03:57:40 -0800

# -*- coding: utf-8 -*-
# Python

# to open a file and write to file
# do

f=open('xfile.txt','w')
# this creates a file "object" and name it f.

# the second argument of open can be
# 'w' for write (overwrite exsiting file)
# 'a' for append (ditto)
# 'r' or read only

# to actually print to file or read from
# file, one uses methods of file
# objects. e.g.

# reading entire file
# text = f.read()

# reading the one line
# line = f.realine()

# reading entire file as a list, of lines
# mylist = f.readlines()

# to write to file, do
f.write('yay, first line!\n')

# when you are done, close the file
f.close()

# closing files saves memory and is
# proper in large programs.

# see
# http://python.org/doc/2.3.4/tut/node9.html

# or in Python terminal,
# type help() then topic FILES

# try to write a program that read in a
# file and print it to a new file.

------------------------
# in perl, similar functionality exists.
# their construct is quite varied.

# example of reading in file
# and print it out
# (first, save this file as x.pl)
open(f,"<x.pl") or die "error: $!";
while ($line = <f>) {print $line}
close(f) or die "error: $!";
print "am printing myself\n";

# the above is a so called "idiom"
# meaning that it is the way such is
# done in a particular language, as in
# English.

# note, the f really should be F in Perl
# by some references, but can also be
# lower case f or even "f". All are not
# uncommon. There is no clear reason for
# why or what should be or what
# is the difference. Usually it's
# not worthwhile to question in
# Perl. ">x.pl" would be for write to
# file. The <f> tells perl the file
# object, and when Perl sees t=<> it
# reads a line. (usually, but technically
# depending on some predefined
# variables...) The f they call "file handle".
# ... see
# perldoc -tf open
# to begin understanding.

------------
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if you are reading it on a web page, program examples may not run
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Xah
  xah@xahlee.org
  http://xahlee.org/PageTwo_dir/more.html

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