Re: Python's regular expression help
On Apr 29, 11:49 am, Tim Chase wrote:
> On 04/29/2010 01:00 PM, goldtech wrote:
>
> > Trying to start out with simple things but apparently there's some
> > basics I need help with. This works OK:
> import re
> p = re.compile('(ab*)(sss)')
> m = p.match( 'absss' )
>
> f=r'abss'
> f
> > 'abss'
> m = p.match( f )
> m.group(0)
> > Traceback (most recent call last):
> > File "", line 1, in
> > m.group(0)
> > AttributeError: 'NoneType' object has no attribute 'group'
>
> 'absss' != 'abss'
>
> Your regexp looks for 3 "s", your "f" contains only 2. So the
> regexp object doesn't, well, match. Try
>
> f = 'absss'
>
> and it will work. As an aside, using raw-strings for this text
> doesn't change anything, but if you want, you _can_ write it as
>
> f = r'absss'
>
> if it will make you feel better :)
>
> > How do I implement a regex on a multiline string? I thought this
> > might work but there's problem:
>
> p = re.compile('(ab*)(sss)', re.S)
> m = p.match( 'ab\nsss' )
> m.group(0)
> > Traceback (most recent call last):
> > File "", line 1, in
> > m.group(0)
> > AttributeError: 'NoneType' object has no attribute 'group'
>
> Well, it depends on what you want to do -- regexps are fairly
> precise, so if you want to allow whitespace between the two, you
> can use
>
> r = re.compile(r'(ab*)\s*(sss)')
>
> If you want to allow whitespace anywhere, it gets uglier, and
> your capture/group results will contain that whitespace:
>
> r'(a\s*b*)\s*(s\s*s\s*s)'
>
> Alternatively, if you don't want to allow arbitrary whitespace
> but only newlines, you can use "\n*" instead of "\s*"
>
> -tkc
Yes, most of my problem is w/my patterns not w/any python re syntax.
I thought re.S will take a multiline string with any spaces or
newlines and make it appear as one line to the regex. Make "/n" be
ignored in a way...still playing w/it. Thanks for the help!
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Re: Python's regular expression help
On 04/29/2010 01:00 PM, goldtech wrote:
Trying to start out with simple things but apparently there's some
basics I need help with. This works OK:
import re
p = re.compile('(ab*)(sss)')
m = p.match( 'absss' )
f=r'abss'
f
'abss'
m = p.match( f )
m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
'absss' != 'abss'
Your regexp looks for 3 "s", your "f" contains only 2. So the
regexp object doesn't, well, match. Try
f = 'absss'
and it will work. As an aside, using raw-strings for this text
doesn't change anything, but if you want, you _can_ write it as
f = r'absss'
if it will make you feel better :)
How do I implement a regex on a multiline string? I thought this
might work but there's problem:
p = re.compile('(ab*)(sss)', re.S)
m = p.match( 'ab\nsss' )
m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
Well, it depends on what you want to do -- regexps are fairly
precise, so if you want to allow whitespace between the two, you
can use
r = re.compile(r'(ab*)\s*(sss)')
If you want to allow whitespace anywhere, it gets uglier, and
your capture/group results will contain that whitespace:
r'(a\s*b*)\s*(s\s*s\s*s)'
Alternatively, if you don't want to allow arbitrary whitespace
but only newlines, you can use "\n*" instead of "\s*"
-tkc
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Re: Python's regular expression help
goldtech wrote:
Hi,
Trying to start out with simple things but apparently there's some
basics I need help with. This works OK:
import re
p = re.compile('(ab*)(sss)')
m = p.match( 'absss' )
m.group(0)
'absss'
m.group(1)
'ab'
m.group(2)
'sss'
...
But two questions:
How can I operate a regex on a string variable?
I'm doing something wrong here:
f=r'abss'
f
'abss'
m = p.match( f )
m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
Look closely: the regex contains 3 letter 's', but the string referred
to by f has only 2.
How do I implement a regex on a multiline string? I thought this
might work but there's problem:
p = re.compile('(ab*)(sss)', re.S)
m = p.match( 'ab\nsss' )
m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
Thanks for the newbie regex help, Lee
The string contains a newline between the 'b' and the 's', but the regex
isn't expecting any newline (or any other character) between the 'b' and
the 's', hence no match.
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Re: Python's regular expression help
Le 29/04/2010 20:00, goldtech a écrit :
Hi,
Trying to start out with simple things but apparently there's some
basics I need help with. This works OK:
import re
p = re.compile('(ab*)(sss)')
m = p.match( 'absss' )
m.group(0)
'absss'
m.group(1)
'ab'
m.group(2)
'sss'
...
But two questions:
How can I operate a regex on a string variable?
I'm doing something wrong here:
f=r'abss'
f
'abss'
m = p.match( f )
m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
How do I implement a regex on a multiline string? I thought this
might work but there's problem:
p = re.compile('(ab*)(sss)', re.S)
m = p.match( 'ab\nsss' )
m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
Thanks for the newbie regex help, Lee
for multiline, I use re.DOTALL
I do not know match(), findall is pretty efficient :
my = "LINK"
res = re.findall(">(.*?)<",my)
>>> res
['LINK']
Dorian
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Python's regular expression help
Hi,
Trying to start out with simple things but apparently there's some
basics I need help with. This works OK:
>>> import re
>>> p = re.compile('(ab*)(sss)')
>>> m = p.match( 'absss' )
>>> m.group(0)
'absss'
>>> m.group(1)
'ab'
>>> m.group(2)
'sss'
...
But two questions:
How can I operate a regex on a string variable?
I'm doing something wrong here:
>>> f=r'abss'
>>> f
'abss'
>>> m = p.match( f )
>>> m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
How do I implement a regex on a multiline string? I thought this
might work but there's problem:
>>> p = re.compile('(ab*)(sss)', re.S)
>>> m = p.match( 'ab\nsss' )
>>> m.group(0)
Traceback (most recent call last):
File "", line 1, in
m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
>>>
Thanks for the newbie regex help, Lee
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Re: A bug in Python's regular expression engine?
On Nov 27, 10:52 am, MonkeeSage <[EMAIL PROTECTED]> wrote:
> On Nov 27, 10:19 am, "Just Another Victim of the Ambient Morality"
>
> <[EMAIL PROTECTED]> wrote:
> > That is funny. Thank you for your help...
> > Just for clarification, what does the "r" in your code do?
>
> It means a "raw" string (as you know ruby, think of it like %w{}):
>
> This page explains about string literal prefixes (see especially the
> end-notes):
>
> http://docs.python.org/ref/strings.html
>
> HTH,
> Jordan
Arg! %w{} should have said %q{}
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Re: A bug in Python's regular expression engine?
On Nov 27, 10:19 am, "Just Another Victim of the Ambient Morality"
<[EMAIL PROTECTED]> wrote:
> That is funny. Thank you for your help...
> Just for clarification, what does the "r" in your code do?
It means a "raw" string (as you know ruby, think of it like %w{}):
This page explains about string literal prefixes (see especially the
end-notes):
http://docs.python.org/ref/strings.html
HTH,
Jordan
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Re: A bug in Python's regular expression engine?
"Paul Hankin" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> On Nov 27, 3:48 pm, "Just Another Victim of the Ambient Morality"
> <[EMAIL PROTECTED]> wrote:
>> This won't compile for me:
>>
>> regex = re.compile('(.*\\).*')
>>
>> I get the error:
>>
>> sre_constants.error: unbalanced parenthesis
>>
>> I'm running Python 2.5 on WinXP. I've tried this expression with
>> another RE engine in another language and it works just fine which leads
>> me
>> to believe the problem is Python. Can anyone confirm or deny this bug?
>
> Your code is equivalent to:
> regex = re.compile(r'(.*\).*')
>
> Written like this, it's easier to see that you've started a regular
> expression group with '(', but it's never closed since your closed
> parenthesis is escaped (which causes it to match a literal ')' when
> used). Hence the reported error (which isn't a bug).
>
> Perhaps you meant this?
> regex = re.compile(r'(.*\\).*')
>
> This matches any number of characters followed by a backslash (group
> 1), and then any number of characters. If you're using this for path
> splitting filenames under Windows, you should look at os.path.split
> instead of writing your own.
Indeed, I did end up using os.path functions, instead.
I think I see what's going on. Backslash has special meaning in both
the regular expression and Python string declarations. So, my version
should have been something like this:
regex = re.compile('(.*).*')
That is funny. Thank you for your help...
Just for clarification, what does the "r" in your code do?
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Re: A bug in Python's regular expression engine?
On Nov 27, 3:48 pm, "Just Another Victim of the Ambient Morality"
<[EMAIL PROTECTED]> wrote:
> This won't compile for me:
>
> regex = re.compile('(.*\\).*')
>
> I get the error:
>
> sre_constants.error: unbalanced parenthesis
>
> I'm running Python 2.5 on WinXP. I've tried this expression with
> another RE engine in another language and it works just fine which leads me
> to believe the problem is Python. Can anyone confirm or deny this bug?
Your code is equivalent to:
regex = re.compile(r'(.*\).*')
Written like this, it's easier to see that you've started a regular
expression group with '(', but it's never closed since your closed
parenthesis is escaped (which causes it to match a literal ')' when
used). Hence the reported error (which isn't a bug).
Perhaps you meant this?
regex = re.compile(r'(.*\\).*')
This matches any number of characters followed by a backslash (group
1), and then any number of characters. If you're using this for path
splitting filenames under Windows, you should look at os.path.split
instead of writing your own.
HTH
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Re: A bug in Python's regular expression engine?
On 2007-11-27, Just Another Victim of the Ambient Morality
<[EMAIL PROTECTED]> wrote:
> This won't compile for me:
>
>
> regex = re.compile('(.*\\).*')
>
> I get the error:
> sre_constants.error: unbalanced parenthesis
Hint 1: Always assume that errors are in your own code. Blaming
library code and language implementations will get you nowhere
most of the time.
Hint 2: regular expressions and Python strings use the same
escape character.
Hint 3: Consult the Python documentation about raw strings, and
what they are meant for.
--
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Re: A bug in Python's regular expression engine?
Just Another Victim of the Ambient Morality wrote:
> This won't compile for me:
>
>
> regex = re.compile('(.*\\).*')
>
>
> I get the error:
>
>
> sre_constants.error: unbalanced parenthesis
>
>
> I'm running Python 2.5 on WinXP. I've tried this expression with
> another RE engine in another language and it works just fine which leads
> me
> to believe the problem is Python. Can anyone confirm or deny this bug?
It pretty much says what the problem is - you escaped the closing
parenthesis, resulting in an invalid rex.
Either use raw-strings or put the proper amount of backslashes in your
string:
regex = re.compile(r'(.*\\).*') # raw string literal
regex = re.compile('(.*).*') # two consecutive \es, meaning an escaped
one
Diez
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A bug in Python's regular expression engine?
This won't compile for me:
regex = re.compile('(.*\\).*')
I get the error:
sre_constants.error: unbalanced parenthesis
I'm running Python 2.5 on WinXP. I've tried this expression with
another RE engine in another language and it works just fine which leads me
to believe the problem is Python. Can anyone confirm or deny this bug?
Thank you...
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Re: Python's regular expression?
Dave Hansen wrote: > On Wed, 10 May 2006 06:44:27 GMT in comp.lang.python, Edward Elliott > <[EMAIL PROTECTED]> wrote: > > > > > > Would I recommend perl for readable, maintainable code? No, not > > when better options like Python are available. But it can be done > > with some effort. > > I'm reminded of a comment made a few years ago by John Levine, > moderator of comp.compilers. He said something like "It's clearly > possible to write good code in C++. It's just that no one does." Reminds me of the quote that used to appear on the front page of the ViewCVS project (seems to have gone now that they've moved and renamed themselves to ViewVC). Can't recall the attribution off the top of my head: "[Perl] combines the power of C with the readability of PostScript" Scathing ... but very funny :-) Dave. -- -- http://mail.python.org/mailman/listinfo/python-list
Re: Python's regular expression?
On Wed, 10 May 2006 06:44:27 GMT in comp.lang.python, Edward Elliott <[EMAIL PROTECTED]> wrote: > >Would I recommend perl for readable, maintainable code? No, not when better >options like Python are available. But it can be done with some effort. I'm reminded of a comment made a few years ago by John Levine, moderator of comp.compilers. He said something like "It's clearly possible to write good code in C++. It's just that no one does." Regards, -=Dave -- Change is inevitable, progress is not. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python's regular expression?
bruno at modulix wrote: > From a readability/maintenance POV, Perl is a perfect nightmare. It's certainly true that perl lacks the the eminently readable quality of python. But then so do C, C++, Java, and a lot of other languages. And I'll grant you that perl is more susceptible to the 'executable line-noise' style than most other languages. This results from its heritage as a quick-and-dirty awk/sed type text processing language. But perl doesn't *have* to look that way, and not every perl program is a 'perfect nightmare'. If you follow good practices like turning on strict checking, using readable variable names, avoiding $_, etc, you can produce pretty readable and maintainable code. It takes some discipline, but it's very doable. I've worked with some perl programs for over 5 years without any trouble. About the only thing you can't avoid are the sigils everywhere. Would I recommend perl for readable, maintainable code? No, not when better options like Python are available. But it can be done with some effort. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python's regular expression?
Mirco Wahab wrote:
> If you wouldn't need dictionary lookup and
> get away with associated categories, all
> you'd have to do would be this:
>
>$PATTERN = qr/
>(blue |white |red)(?{'Colour'})
> | (socks|tights)(?{'Garment'})
> | (boot |shoe |trainer)(?{'Footwear'})
>/x;
>
>$t = 'blue socks and red shoes';
>print "$^R: $^N\n" while( $t=~/$PATTERN/g );
>
> What's the point of all that? IMHO, Python's
> Regex support is quite good and useful, but
> won't give you an edge over Perl's in the end.
If you are desperate to collapse the code down to a single print statement
you can do that easily in Python as well:
>>> PATTERN = '''
(?Pblue |white |red)
| (?Psocks|tights)
| (?Pboot |shoe |trainer)
'''
>>> t = 'blue socks and red shoes'
>>> print '\n'.join("%s:%s" % (match.lastgroup,
match.group(match.lastgroup))
for match in re.finditer(PATTERN, t, re.VERBOSE))
Colour:blue
Garment:socks
Colour:red
Footwear:shoe
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Re: Python's regular expression?
Davy wrote:
> Hi all,
>
(snip)
> Does Python support robust regular expression like Perl?
Yes.
> And Python and Perl's File content manipulation, which is better?
>From a raw perf and write-only POV, Perl clearly beats Python (regarding
I/O, Perl is faster than C - or it least it was the last time I benched
it on a Linux box).
>From a readability/maintenance POV, Perl is a perfect nightmare.
> Any suggestions will be appreciated!
http://pythonology.org/success&story=esr
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p in '[EMAIL PROTECTED]'.split('@')])"
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Re: Python's regular expression?
Hi Duncan
> Nick Craig-Wood wrote:
>> Which translates to
>> match = re.search('(blue|white|red)', t)
>> if match:
>> else:
>> if match:
>> else:
>> if match:
>
> This of course gives priority to colours and only looks for garments or
> footwear if the it hasn't matched on a prior pattern. If you actually
> wanted to match the first occurrence of any of these (or if the condition
> was re.match instead of re.search) then named groups can be a nice way of
> simplifying the code:
A good point. And a good example when to use named
capture group references. This is easily extended
for 'spitting out' all other occuring categories
(see below).
> PATTERN = '''
> (?Pblue|white|red)
> ...
This is one nice thing in Pythons Regex Syntax,
you have to emulate the ?P-thing in other
Regex-Systems more or less 'awk'-wardly ;-)
> For something this simple the titles and group names could be the
> same, but I'm assuming real code might need a bit more.
Non no, this is quite good because it involves
some math-generated table-code lookup.
I managed somehow to extend your example in order
to spit out all matches and their corresponding
category:
import re
PATTERN = '''
(?Pblue |white |red)
| (?Psocks|tights)
| (?Pboot |shoe |trainer)
'''
PATTERN = re.compile(PATTERN , re.VERBOSE)
TITLES = { 'c': 'Colour', 'g': 'Garment', 'f': 'Footwear' }
t = 'blue socks and red shoes'
for match in PATTERN.finditer(t):
grp = match.lastgroup
print "%s: %s" %( TITLES[grp], match.group(grp) )
which writes out the expected:
Colour: blue
Garment: socks
Colour: red
Footwear: shoe
The corresponding Perl-program would look like this:
$PATTERN = qr/
(blue |white |red)(?{'c'})
| (socks|tights)(?{'g'})
| (boot |shoe |trainer)(?{'f'})
/x;
%TITLES = (c =>'Colour', g =>'Garment', f =>'Footwear');
$t = 'blue socks and red shoes';
print "$TITLES{$^R}: $^N\n" while( $t=~/$PATTERN/g );
and prints the same:
Colour: blue
Garment: socks
Colour: red
Footwear: shoe
You don't have nice named match references (?P<..>)
in Perl-5, so you have to emulate this by an ordinary
code assertion (?{..}) an set some value ($^R) on
the fly - which is not that bad in the end (imho).
(?{..}) means "zero with code assertion",
this sets Perl-predefined $^R to its evaluated
value from the {...}
As you can see, the pattern matching related part
reduces from 4 lines to one line.
If you wouldn't need dictionary lookup and
get away with associated categories, all
you'd have to do would be this:
$PATTERN = qr/
(blue |white |red)(?{'Colour'})
| (socks|tights)(?{'Garment'})
| (boot |shoe |trainer)(?{'Footwear'})
/x;
$t = 'blue socks and red shoes';
print "$^R: $^N\n" while( $t=~/$PATTERN/g );
What's the point of all that? IMHO, Python's
Regex support is quite good and useful, but
won't give you an edge over Perl's in the end.
Thanks & Regards
Mirco
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Re: Python's regular expression?
Nick Craig-Wood wrote:
> Which translates to
>
> match = re.search('(blue|white|red)', t)
> if match:
> print "Colour:", match.group(1)
> else:
> match = re.search('(socks|tights)', t)
> if match:
> print "Garment:", match.group(1)
> else:
> match = re.search('(boot|shoe|trainer)', t)
> if match:
>print "Footwear:", match.group(1)
># indented ad infinitum!
This of course gives priority to colours and only looks for garments or
footwear if the it hasn't matched on a prior pattern. If you actually
wanted to match the first occurrence of any of these (or if the condition
was re.match instead of re.search) then named groups can be a nice way of
simplifying the code:
PATTERN = '''
(?Pblue|white|red)
| (?Psocks|tights)
| (?Pboot|shoe|trainer)
'''
PATTERN = re.compile(PATTERN, re.VERBOSE)
TITLES = { 'c': 'Colour', 'g': 'Garment', 'f': 'Footwear' }
match = PATTERN.search(t)
if match:
grp = match.lastgroup
print "%s: %s" % (TITLES[grp], match.group(grp))
For something this simple the titles and group names could be the same, but
I'm assuming real code might need a bit more.
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Re: Python's regular expression?
Mirco Wahab <[EMAIL PROTECTED]> wrote:
> After some minutes in this NG I start to get
> the picture. So I narrowed the above regex-question
> down to a nice equivalence between Perl and Python:
>
> Python:
>
> import re
>
> t = 'blue socks and red shoes'
> if re.match('blue|white|red', t):
> print t
>
> t = 'blue socks and red shoes'
> if re.search('blue|white|red', t):
>print t
>
> Perl:
>
> use Acme::Pythonic;
>
> $t = 'blue socks and red shoes'
> if $t =~ /blue|white|red/:
> print $t
>
> And Python Regexes eventually lost (for me) some of
> their (what I believed) 'clunky appearance' ;-)
If you are used to perl regexes there is one clunkiness of python
regexpes which you'll notice eventually...
Let's make the above example a bit more "real world", ie use the
matched item in some way...
Perl:
$t = 'blue socks and red shoes';
if ( $t =~ /(blue|white|red)/ )
{
print "Colour: $1\n";
}
Which prints
Colour: blue
In python you have to express this like
import re
t = 'blue socks and red shoes'
match = re.search('(blue|white|red)', t)
if match:
print "Colour:", match.group(1)
Note the extra variable "match". You can't do assignment in an
expression in python which makes for the extra verbiosity, and you
need a variable to store the result of the match in (since python
doesn't have the magic $1..$9 variables).
This becomes particularly frustrating when you have to do a series of
regexp matches, eg
if ( $t =~ /(blue|white|red)/ )
{
print "Colour: $1\n";
}
elsif ( $t =~ /(socks|tights)/)
{
print "Garment: $1\n";
}
elsif ( $t =~ /(boot|shoe|trainer)/)
{
print "Footwear: $1\n";
}
Which translates to
match = re.search('(blue|white|red)', t)
if match:
print "Colour:", match.group(1)
else:
match = re.search('(socks|tights)', t)
if match:
print "Garment:", match.group(1)
else:
match = re.search('(boot|shoe|trainer)', t)
if match:
print "Footwear:", match.group(1)
# indented ad infinitum!
You can use a helper class to get over this frustration like this
import re
class Matcher:
def search(self, r,s):
self.value = re.search(r,s)
return self.value
def __getitem__(self, i):
return self.value.group(i)
m = Matcher()
t = 'blue socks and red shoes'
if m.search(r'(blue|white|red)', t):
print "Colour:", m[1]
elif m.search(r'(socks|tights)', t):
print "Garment:", m[1]
elif m.search(r'(boot|shoe|trainer)', t):
print "Footwear:", m[1]
Having made the transition from perl to python a couple of years ago,
I find myself using regexpes much less. In perl everything looks like
it needs a regexp, but python has a much richer set of string methods,
eg .startswith, .endswith, good subscripting and the nice "in"
operator for strings.
--
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Re: Python's regular expression?
Hi John
>> But what would be an appropriate use
>> of search() vs. match()? When to use what?
>
> ReadTheFantasticManual :-)
>From the manual you mentioned, i don't get
the point of 'match'. So why should you use
an extra function entry match(),
re.match('whatever', t):
which is, according to the FM,
equivalent to (a special case of?)
re.search('^whatever', t):
For me, it looks like match() should
be used on simple string comparisons
like a 'ramped up C-strcmp()'.
Or isn't ist? Maybe I dont get it ;-)
Thanks
Mirco
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Re: Python's regular expression?
On 8/05/2006 11:13 PM, Mirco Wahab wrote:
> Hi John
>
>>>import re
>>>
>>>t = 'blue socks and red shoes'
>>>p = re.compile('(blue|white|red)')
>>>if p.match(t):
>> What do you expect when t == "green socks and red shoes"? Is it possible
>> that you mean to use search() rather than match()?
>
> This is interesting.
> What's in this example the difference then between:
I suggest that you (a) read the description on the difference between
search and match in the manual (b) try out search and match on both
your original string and the one I proposed.
>
>import re
>
>t = 'blue socks and red shoes'
>if re.compile('blue|white|red').match(t):
> print t
>
> and
>
>t = 'blue socks and red shoes'
>if re.search('blue|white|red', t):
> print t
[snip]
>
> But what would be an appropriate use
> of search() vs. match()? When to use what?
ReadTheFantasticManual :-)
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Re: Python's regular expression?
Hi Duncan
> There is no need to compile the regular expression in advance in Python
> either:
> ...
> The only advantage to compiling in advance is a small speed up, and most of
> the time that won't be significant.
I read 'some' introductions into Python Regexes
and got confused in the first place when to use
what and why.
After some minutes in this NG I start to get
the picture. So I narrowed the above regex-question
down to a nice equivalence between Perl and Python:
Python:
import re
t = 'blue socks and red shoes'
if re.match('blue|white|red', t):
print t
t = 'blue socks and red shoes'
if re.search('blue|white|red', t):
print t
Perl:
use Acme::Pythonic;
$t = 'blue socks and red shoes'
if $t =~ /blue|white|red/:
print $t
And Python Regexes eventually lost (for me) some of
their (what I believed) 'clunky appearance' ;-)
Thanks
Mirco
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Re: Python's regular expression?
Hi John
>>import re
>>
>>t = 'blue socks and red shoes'
>>p = re.compile('(blue|white|red)')
>>if p.match(t):
>
> What do you expect when t == "green socks and red shoes"? Is it possible
> that you mean to use search() rather than match()?
This is interesting.
What's in this example the difference then between:
import re
t = 'blue socks and red shoes'
if re.compile('blue|white|red').match(t):
print t
and
t = 'blue socks and red shoes'
if re.search('blue|white|red', t):
print t
> There is no need to compile the regex in advance in Python, either.
> Please consider the module-level function search() ...
> if re.search(r"blue|white|red", t):
> # also, no need for () in the regex.
Thats true. Thank you for pointing this out.
But what would be an appropriate use
of search() vs. match()? When to use what?
I answered the posting in the first place
because also I'm coming from a C/C++/Perl
background and trying to get along in Python.
Thanks,
Mirco
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Re: Python's regular expression?
Mirco Wahab wrote:
> Lets see - a really simple find/match
> would look like this in Python:
>
>import re
>
>t = 'blue socks and red shoes'
>p = re.compile('(blue|white|red)')
>if p.match(t):
> print t
>
> which prints the text 't' because of
> the positive pattern match.
>
> In Perl, you write:
>
>use Acme::Pythonic;
>
>$t = 'blue socks and red shoes'
>if ($t =~ /(blue|white|red)/):
> print $t
>
> which is one line shorter (no need
> to compile the regular expression
> in advance).
>
There is no need to compile the regular expression in advance in Python
either:
t = 'blue socks and red shoes'
if re.match('(blue|white|red)', t):
print t
The only advantage to compiling in advance is a small speed up, and most of
the time that won't be significant.
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Re: Python's regular expression?
On 8/05/2006 10:31 PM, Mirco Wahab wrote:
[snip]
>
> Lets see - a really simple find/match
> would look like this in Python:
>
>import re
>
>t = 'blue socks and red shoes'
>p = re.compile('(blue|white|red)')
>if p.match(t):
What do you expect when t == "green socks and red shoes"? Is it possible
that you mean to use search() rather than match()?
> print t
>
> which prints the text 't' because of
> the positive pattern match.
>
> In Perl, you write:
>
>use Acme::Pythonic;
>
>$t = 'blue socks and red shoes'
>if ($t =~ /(blue|white|red)/):
> print $t
>
> which is one line shorter (no need
> to compile the regular expression
> in advance).
There is no need to compile the regex in advance in Python, either.
Please consider the module-level function search() ...
if re.search(r"blue|white|red", t):
# also, no need for () in the regex.
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Re: Python's regular expression?
Hi Davy
> > More similar than Perl ;-)
But C has { }'s everywhere, so has Perl ;-)
> > And what's 'integrated' mean (must include some library)?
Yes. In Python, regular expressions are just
another function library - you use them like
in Java or C.
In Perl, it's part of the core language, you
use the awk-style (eg: /.../) regular expressions
everywhere you want.
If you used regexp in C/C++ before, you can use them
in almost the same way in Python - which may give you
an easy start.
BTW. Python has some fine extensions to the
perl(5)-Regexes, e.g. 'named backreferences'.
But you won't see much regular expressions
in Python code posted to this group, maybe
because it looks clunky - which is unpythonic ;-)
Lets see - a really simple find/match
would look like this in Python:
import re
t = 'blue socks and red shoes'
p = re.compile('(blue|white|red)')
if p.match(t):
print t
which prints the text 't' because of
the positive pattern match.
In Perl, you write:
use Acme::Pythonic;
$t = 'blue socks and red shoes'
if ($t =~ /(blue|white|red)/):
print $t
which is one line shorter (no need
to compile the regular expression
in advance).
> > I like C++ file I/O, is it 'low' or 'high'?
C++ has afaik actually three levels of I/O:
(1) - (from C, very low) operating system level, included
by which provides direct access to operating system
services (read(), write(), lseek() etc.)
(2) - C-Standard-Library buffered IO, included by ,
provides structured 'mid-level' access like (block-) fread()/
fwrite(), line read (fgets()) and formatted I/O (fprintf()/
fscanf())
(3) - C++/streams library (high level, , , ),
which abstracts out the i/o devices, provides the same set of
functionality for any abstract input or output.
Perl provides all three levels of I/O, the 'abstracting' is introduced
by modules which tie 'handle variables' to anything that may receive
or send data.
Python also does a good job on all three levels, but provides
the (low level) operating system I/O by external modules (afaik).
I didn't do much I/O in Python, so I can't say much here.
Regards
Mirco
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Re: Python's regular expression?
By the way, is there any tutorial talk about how to use the Python Shell (IDE). I wish it simple like VC++ :) Regards, Davy -- http://mail.python.org/mailman/listinfo/python-list
Re: Python's regular expression?
Hi Mirco, Thank you! More similar than Perl ;-) And what's 'integrated' mean (must include some library)? I like C++ file I/O, is it 'low' or 'high'? Regards, Davy -- http://mail.python.org/mailman/listinfo/python-list
Re: Python's regular expression?
Hi Davy wrote: > I am a C/C++/Perl user and want to switch to Python OK > (I found Python is more similar to C). ;-) More similar than what? > Does Python support robust regular expression like Perl? It supports them fairly good, but it's not 'integrated' - at least it feels not integrated for me ;-) If you did a lot of Perl, you know what 'integrated' means ... > And Python and Perl's File content manipulation, which is better? What is a 'file content manipulation'? Did you mean 'good xxx level file IO', where xxx means either 'low' or 'high'? > Any suggestions will be appreciated! Just try to start a small project in Python - from source that you already have in C or Perl or something. Regards Mirco -- http://mail.python.org/mailman/listinfo/python-list
Re: Python's regular expression?
"Davy" <[EMAIL PROTECTED]> writes: > Does Python support robust regular expression like Perl? Yep, Python regular expression is robust. Have a look at the Regex Howto: http://www.amk.ca/python/howto/regex/ and the re module: http://docs.python.org/lib/module-re.html -- Lawrence - http://www.oluyede.org/blog "Nothing is more dangerous than an idea if it's the only one you have" - E. A. Chartier -- http://mail.python.org/mailman/listinfo/python-list
Python's regular expression?
Hi all, I am a C/C++/Perl user and want to switch to Python (I found Python is more similar to C). Does Python support robust regular expression like Perl? And Python and Perl's File content manipulation, which is better? Any suggestions will be appreciated! Best regards, Davy -- http://mail.python.org/mailman/listinfo/python-list
ANN: pyregex 0.5 - command line tools for Python's regular expression
pyregex is a command line tools for constructing and testing Python's
regular expression. Features includes text highlighting, detail break
down of match groups, substitution and a syntax quick reference. It is
released in the public domain.
Screenshot and download from
http://tungwaiyip.info/software/pyregex.html.
Wai Yip Tung
Usage: pyregex.py [options] "-"|filename regex [replacement [count]]
Test Python regular expressions. Specify test data's filename or use
"-"
to enter test text from console. Optionally specify a replacement text.
Options:
-f filter mode
-n nnn limit to examine the first nnn lines. default no limit.
-m show only matched line. default False
Regular Expression Syntax
Special Characters
. matches any character except a newline
^ matches the start of the string
$ matches the end of the string or just before the newline at the
end of
the string
* matches 0 or more repetitions of the preceding RE
+ matches 1 or more repetitions of the preceding RE
? matches 0 or 1 repetitions of the preceding RE
{m} exactly m copies of the previous RE should be matched
{m,n} matches from m to n repetitions of the preceding RE
\ either escapes special characters or signals a special sequence
[] indicate a set of characters. Characters can be listed
individually,
or a range of characters can be indicated by giving two
characters and
separating them by a "-". Special characters are not active
inside sets
Including a "^" as the first character match the complement of
the set
| A|B matches either A or B
(...) indicates the start and end of a group
(?...) this is an extension notation. See documentation for detail
(?iLmsux) I ignorecase; L locale; M multiline; S dotall; U unicode; X
verbose
*, +, ? and {m,n} are greedy. Append the ? qualifier to match
non-greedily.
Special Sequences
\number matches the contents of the group of the same number. Groups
are
numbered starting from 1
\A matches only at the start of the string
\b matches the empty string at the beginning or end of a word
\B matches the empty string not at the beginning or end of a word
\d matches any decimal digit
\D matches any non-digit character
\guse the substring matched by the group named 'name' for sub()
\s matches any whitespace character
\S matches any non-whitespace character
\w matches any alphanumeric character and the underscore
\W matches any non-alphanumeric character
\Z matches only at the end of the string
See the Python documentation on Regular Expression Syntax for more
detail
http://docs.python.org/lib/re-syntax.html
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