[Tutor] Translating to Python [perl --> python]

[Danny Yoo]

On Mon, 1 Jul 2002, Kyle Babich wrote:

> Could someone show me how to translate this to python from perl?

Hi Kyle,

Welcome!  Let's see what a translation might look like between Perl and
Python.



> #!/usr/bin/perl -wT
> use strict;

Python is always in "strict" mode in a sense --- anything bad that happens
will raise an Exception.  Python's magic line will probably look like:

#!/usr/bin/env python





> use CGI qw/ :standard /;

In Python, module importing is done through the 'import' keyword.  Python
does have a 'cgi' module, so we can do:

###
import cgi
###

with similar effects.

See:

    http://www.python.org/doc/lib/module-cgi.html

for more details on the 'cgi' module.



By the way, Python provides a really nice debugging module called 'cgitb'
that prints out a nice traceback if there are bugs in the module.  Rather
than get a rude 'Internal Server Error', we can have our Python script
display a nicely formatted error page by doing:

###
import cgitb
cgitb.enable()
###




> print header ( 'text/html' );

I don't know if the Python cgi module has a header() utility function, but
we can do this for a similar effect:

###
print "Content-type: text/html\n\n"
###




> my $c = param('c');
> my $content = "c";
> 	if ($c eq "abc") {
> 		$content = qq{abc123};
> 	} elsif ($c eq "def") {
> 		$content = qq{def456};
> 	} else {
> 		print "error:  content failed\n";
> 	}


Python's cgi module provides an object that we use to pull out parameters.
Here's what it might look like:

###
form = cgi.FieldStorage()
c = cgi['c'].value
content = 'c'
if c == 'abc':
    content = "abc123"
elif c == 'def':
    content = "def456"
else:
    print "error: content failed\n" ## shouldn't we raise an error here?
###





> open(TEXT,"text.txt") or die ("error:  text.txt failed\n");
> 	my $text = <TEXT>;
> close(TEXT) or die("error:  close text.txt failed\n");


File opening in Python implicitly raises an IOError if bad things happen,
so the "die" part is implied.

###
file = open("text.txt")
text = file.read()
file.close()
###



> print <<"EndOfHTML";
>
> $content
>
> <br>&nbsp;<br>&nbsp;<br>&nbsp;
>
> $text
>
> EndOfHTML

Python provides a string formatting operation that can span across several
lines:

###
print """

%(content)s


<br>&nbsp;<br>&nbsp;<br>&nbsp;

%(text)s

""" % vars()
###





Let's put everything together to see what the final product looks like.
I'll do a little rearrangement to make the program flow a little nicer:

###
# Translation of Kyle's Perl program into Python
import cgi
import cgitb
cgitb.enable()


form = cgi.FieldStorage()
c = cgi['c'].value
content = 'c'
if c == 'abc':
    content = "abc123"
elif c == 'def':
    content = "def456"
else:
    print "error: content failed\n"

file = open("text.txt")
text = file.read()
file.close()


print "Content-type: text/html\n\n"
print """

%(content)s


<br>&nbsp;<br>&nbsp;<br>&nbsp;

%(text)s

""" % vars()
###


This is still a little awkward as far as Python programs go --- I'd like
to break things down into separate functions to make the code's intent
clearer, and to avoid having global variables spill out everywhere.


Hope this helps!