regular expression: perl ==> python

[les_ander]

Hi,
i am so use to perl's regular expression that i find it hard
to memorize the functions in python; so i would appreciate if
people can tell me some equivalents.

1) In perl:
$line = "The food is under the bar in the barn.";
if ( $line =~ /foo(.*)bar/ ) { print "got <$1>\n"; }

in python, I don't know how I can do this?
How does one capture the $1? (I know it is \1 but it is still not clear
how I can simply print it.
thanks

[Steven Bethard]

le*******@yahoo .com wrote:

1) In perl:
$line = "The food is under the bar in the barn.";
if ( $line =~ /foo(.*)bar/ ) { print "got <$1>\n"; }

in python, I don't know how I can do this?

I don't know Perl very well, but I believe this is more or less the
equivalent:

import re
line = "The food is under the bar in the barn."
matcher = re.compile(r'fo o(.*)bar')
match = matcher.search( line)
print 'got <%s>' % match.group(1) got <d is under the bar in the >

Of course, you can do this in fewer lines if you like:
print 'got <%s>' % re.search(r'foo (.*bar)', line).group(1)

got <d is under the bar in the bar>

Steve

[Fredrik Lundh]

<le*******@yaho o.com> wrote:

i am so use to perl's regular expression that i find it hard
to memorize the functions in python; so i would appreciate if
people can tell me some equivalents.

1) In perl:
$line = "The food is under the bar in the barn.";
if ( $line =~ /foo(.*)bar/ ) { print "got <$1>\n"; }

in python, I don't know how I can do this?
How does one capture the $1? (I know it is \1 but it is still not clear
how I can simply print it.

in Python, the RE machinery returns match objects, which has methods
that let you dig out more information about the match. "captured groups"
are available via the "group" method:

m = re.search(..., line)
if m:
print "got", m.group(1)

see the regex howto (or the RE chapter in the library reference) for more
information:

http://www.amk.ca/python/howto/regex/

</F>

[JZ]

Dnia 21 Dec 2004 21:12:09 -0800, le*******@yahoo .com napisa³(a):

1) In perl:
$line = "The food is under the bar in the barn.";
if ( $line =~ /foo(.*)bar/ ) { print "got <$1>\n"; }

in python, I don't know how I can do this?
How does one capture the $1? (I know it is \1 but it is still not clear
how I can simply print it.
thanks

import re
line = "The food is under the bar in the barn."
if re.search(r'foo (.*)bar',line):
print 'got %s\n' % _.group(1)

--
JZ ICQ:6712522
http://zabiello.om

[Fredrik Lundh]

"JZ" <wn******@mnovr yyb.pbz> wrote:

import re
line = "The food is under the bar in the barn."
if re.search(r'foo (.*)bar',line):
print 'got %s\n' % _.group(1)

Traceback (most recent call last):
File "jz.py", line 4, in ?
print 'got %s\n' % _.group(1)
NameError: name '_' is not defined

</F>

[Doug Holton]

Fredrik Lundh wrote:

"JZ" <wn******@mnovr yyb.pbz> wrote:

import re
line = "The food is under the bar in the barn."
if re.search(r'foo (.*)bar',line):
print 'got %s\n' % _.group(1)

Traceback (most recent call last):
File "jz.py", line 4, in ?
print 'got %s\n' % _.group(1)
NameError: name '_' is not defined

He was using the python interactive prompt, which I suspect you already
knew.

[JZ]

Dnia Wed, 22 Dec 2004 10:27:39 +0100, Fredrik Lundh napisa³(a):

import re
line = "The food is under the bar in the barn."
if re.search(r'foo (.*)bar',line):
print 'got %s\n' % _.group(1)

Traceback (most recent call last):
File "jz.py", line 4, in ?
print 'got %s\n' % _.group(1)
NameError: name '_' is not defined

I forgot to add: I am using Python 2.3.4/Win32 (from ActiveState.com ). The
code works in my interpreter.

--
JZ

[Fredrik Lundh]

"JZ" wrote:

import re
line = "The food is under the bar in the barn."
if re.search(r'foo (.*)bar',line):
print 'got %s\n' % _.group(1)

Traceback (most recent call last):
File "jz.py", line 4, in ?
print 'got %s\n' % _.group(1)
NameError: name '_' is not defined

I forgot to add: I am using Python 2.3.4/Win32 (from ActiveState.com ). The
code works in my interpreter.

only if you type it into the interactive prompt. see:

http://www.python.org/doc/2.4/tut/no...00000000000000

"In interactive mode, the last printed expression is assigned to the variable _.
This means that when you are using Python as a desk calculator, it is some-
what easier to continue calculations /.../"

the "_" symbol has no special meaning when you run a Python program, so the
"if re.search" construct won't work.

</F>

[JZ]

Dnia Wed, 22 Dec 2004 16:55:55 +0100, Fredrik Lundh napisa³(a):

the "_" symbol has no special meaning when you run a Python program,

That's right. So the final code will be:

import re
line = "The food is under the bar in the barn."
found = re.search('foo( .*)bar',line)
if found: print 'got %s\n' % found.group(1)

--
JZ ICQ:6712522
http://zabiello.com

[Nick Craig-Wood]

> 1) In perl:

$line = "The food is under the bar in the barn.";
if ( $line =~ /foo(.*)bar/ ) { print "got <$1>\n"; }

in python, I don't know how I can do this?
How does one capture the $1? (I know it is \1 but it is still not clear
how I can simply print it.
thanks

Fredrik Lundh <fr*****@python ware.com> wrote: "JZ" <wn******@mnovr yyb.pbz> wrote:

import re
line = "The food is under the bar in the barn."
if re.search(r'foo (.*)bar',line):
print 'got %s\n' % _.group(1)

Traceback (most recent call last):
File "jz.py", line 4, in ?
print 'got %s\n' % _.group(1)
NameError: name '_' is not defined

I've found that a slight irritation in python compared to perl - the
fact that you need to create a match object (rather than relying on
the silver thread of $_ (etc) running through your program ;-)

import re
line = "The food is under the bar in the barn."
m = re.search(r'foo (.*)bar',line)
if m:
print 'got %s\n' % m.group(1)

This becomes particularly irritating when using if, elif etc, to
match a series of regexps, eg

line = "123123"
m = re.search(r'^(\ d+)$', line)
if m:
print "int",int(m.gro up(1))
else:
m = re.search(r'^(\ d*\.\d*)$', line)
if m:
print "float",float(m .group(1))
else:
print "unknown thing", line

The indentation keeps growing which looks rather untidy compared to
the perl

$line = "123123";
if ($line =~ /^(\d+)$/) {
print "int $1\n";
}
elsif ($line =~ /^(\d*\.\d*)$/) {
print "float $1\n";
}
else {
print "unknown thing $line\n";
}

Is there an easy way round this? AFAIK you can't assign a variable in
a compound statement, so you can't use elif at all here and hence the
problem?

I suppose you could use a monstrosity like this, which relies on the
fact that list.append() returns None...

line = "123123"
m = []
if m.append(re.sea rch(r'^(\d+)$', line)) or m[-1]:
print "int",int(m[-1].group(1))
elif m.append(re.sea rch(r'^(\d*\.\d *)$', line)) or m[-1]:
print "float",flo at(m[-1].group(1))
else:
print "unknown thing", line

--
Nick Craig-Wood <ni**@craig-wood.com> -- http://www.craig-wood.com/nick