[perl-python] 20050121 file reading & writing

Discussion in 'Perl Misc' started by Xah Lee, Jan 22, 2005.

  1. Xah Lee

    Xah Lee Guest

    # -*- 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.

    ------------
    Note: this post is from the Perl-Python a-day mailing list at
    http://groups.yahoo.com/group/perl-python/
    to subscribe, send an email to
    if you are reading it on a web page, program examples may not run
    because html conversion often breaks the code.
    Xah

    http://xahlee.org/PageTwo_dir/more.html
     
    Xah Lee, Jan 22, 2005
    #1
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  2. Xah Lee wrote:

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


    are you sure you didn't forget something?

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


    wrong

    > [...]


    Maybe you didn't get the fact the you won't see a flame starting between
    python people and perl friends?

    throw yourself somewhere and... Xah.flush()
    --
    Gian Mario Tagliaretti
    PyGTK GUI programming
    http://www.parafernalia.org/pygtk/
     
    Gian Mario Tagliaretti, Jan 22, 2005
    #2
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  3. Xah Lee

    Anno Siegel Guest

    Gian Mario Tagliaretti <> wrote in comp.lang.perl.misc:
    > Xah Lee wrote:
    >
    > > # the second argument of open can be
    > > # 'w' for write (overwrite exsiting file)
    > > # 'a' for append (ditto)


    In Python, appending to a file overwrites it? Interesting...

    > > # 'r' or read only

    >
    > are you sure you didn't forget something?
    >
    > > # reading the one line
    > > # line = f.realine()

    >
    > wrong
    >
    > > [...]

    >
    > Maybe you didn't get the fact the you won't see a flame starting between
    > python people and perl friends?


    The Perl part, thankfully snipped, is so wrong that it hurts. This stuff
    is so sloppy, it isn't even good for flame bait.

    Anno
     
    Anno Siegel, Jan 23, 2005
    #3
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