Look for a string on a file and get its line number

[Horacius ReX]

Hi,

I have to search for a string on a big file. Once this string is
found, I would need to get the number of the line in which the string
is located on the file. Do you know how if this is possible to do in
python ?

Thanks

[Jeroen Ruigrok van der Werven]

-On [20080108 09:21], Horacius ReX (ho**********@g mail.com) wrote:

>I have to search for a string on a big file. Once this string is
found, I would need to get the number of the line in which the string
is located on the file. Do you know how if this is possible to do in
python ?

(Assuming ASCII, otherwise check out codecs.open().)

big_file = open('bigfile.t xt', 'r')

line_nr = 0
for line in big_file:
line_nr += 1
has_match = line.find('my-string')
if has_match 0:
print 'Found in line %d' % (line_nr)

Something to this effect.

--
Jeroen Ruigrok van der Werven <asmodai(-at-)in-nomine.org/ asmodai
イェルーン ラウフãƒ*ッ ク ヴァン デル ウェルヴェ ン
http://www.in-nomine.org/ | http://www.rangaku.org/
If you think that you know much, you know little...

[John Machin]

On Jan 8, 7:33 pm, Jeroen Ruigrok van der Werven <asmo...@in-
nomine.orgwrote :

-On [20080108 09:21], Horacius ReX (horacius....@g mail.com) wrote:

I have to search for a string on a big file. Once this string is
found, I would need to get the number of the line in which the string
is located on the file. Do you know how if this is possible to do in
python ?

(Assuming ASCII, otherwise check out codecs.open().)

big_file = open('bigfile.t xt', 'r')

line_nr = 0
for line in big_file:
line_nr += 1
has_match = line.find('my-string')
if has_match 0:

Make that >=

| >>'fubar'.find( 'fu')
| 0
| >>>

print 'Found in line %d' % (line_nr)

[Jeroen Ruigrok van der Werven]

-On [20080108 09:51], John Machin (sj******@lexic on.net) wrote:

>Make that >=

Right you are. Sorry, was doing it quickly from work. ;)

And I guess the find will also be less precise if the word you are looking is
a smaller part of a bigger word. E.g. find 'door' in a line that has 'doorway'
in it.

So 't is merely for inspiration. ;)

--
Jeroen Ruigrok van der Werven <asmodai(-at-)in-nomine.org/ asmodai
イェルーン ラウフãƒ*ッ ク ヴァン デル ウェルヴェ ン
http://www.in-nomine.org/ | http://www.rangaku.org/

>From morning to night I stayed out of sight / Didn't recognise I'd become

No more than alive I'd barely survive / In a word, overrun...

[Jeroen Ruigrok van der Werven]

-On [20080108 09:51], John Machin (sj******@lexic on.net) wrote:

>Make that >=

| >>'fubar'.find( 'fu')

Or even just:

if 'my-string' in line:
...

Same caveat emptor applies though.

--
Jeroen Ruigrok van der Werven <asmodai(-at-)in-nomine.org/ asmodai
イェルーン ラウフãƒ*ッ ク ヴァン デル ウェルヴェ ン
http://www.in-nomine.org/ | http://www.rangaku.org/
We're walking this earth. We're walking this shining earth...

[Martin Marcher]

Jeroen Ruigrok van der Werven wrote:

-On [20080108 09:21], Horacius ReX (ho**********@g mail.com) wrote:

>>I have to search for a string on a big file. Once this string is
found, I would need to get the number of the line in which the string
is located on the file. Do you know how if this is possible to do in
python ?

(Assuming ASCII, otherwise check out codecs.open().)

big_file = open('bigfile.t xt', 'r')

line_nr = 0
for line in big_file:
line_nr += 1
has_match = line.find('my-string')
if has_match 0:
print 'Found in line %d' % (line_nr)

Something to this effect.

apart from that look at the linecache module. If it's a big file it could
help you with subsequent access to the line in question

hth
martin

--
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http://feeds.feedburner.com/NoneIsYours

You are not free to read this message,
by doing so, you have violated my licence
and are required to urinate publicly. Thank you.

[Ryan Ginstrom]

On Behalf Of Horacius ReX

I have to search for a string on a big file. Once this string
is found, I would need to get the number of the line in which
the string is located on the file. Do you know how if this is
possible to do in python ?

This should be reasonable:

>>for num, line in enumerate(open( "/python25/readme.txt")):

if "Guido" in line:
print "Found Guido on line", num
break
Found Guido on line 1296

>>>

Regards,
Ryan Ginstrom

[Wildemar Wildenburger]

Jeroen Ruigrok van der Werven wrote:

line_nr = 0
for line in big_file:
line_nr += 1
has_match = line.find('my-string')
if has_match 0:
print 'Found in line %d' % (line_nr)

Style note:
May I suggest enumerate (I find the explicit counting somewhat clunky)
and maybe turning it into a generator (I like generators):

def lines(big_file, pattern="my string"):
for n, line in enumerate(big_f ile):
if pattern in line:
print 'Found in line %d' % (n)
yield n

or for direct use, how about a simple list comprehension:

lines = [n for (n, line) in enumerate(big_f ile) if "my string" in line]

(If you're just going to iterate over the result, that is you do not
need indexing, replace the brackets with parenthesis. That way you get a
generator and don't have to build a complete list. This is especially
useful if you expect many hits.)

Just a note.

regards
/W

[Jeroen Ruigrok van der Werven]

-On [20080108 12:59], Wildemar Wildenburger (la*********@kl apptsowieso.net ) wrote:

>Style note:
May I suggest enumerate (I find the explicit counting somewhat clunky)
and maybe turning it into a generator (I like generators):

Sure, I still have a lot to discover myself with Python.

I'll study your examples, thanks. :)

--
Jeroen Ruigrok van der Werven <asmodai(-at-)in-nomine.org/ asmodai
イェルーン ラウフãƒ*ッ ク ヴァン デル ウェルヴェ ン
http://www.in-nomine.org/ | http://www.rangaku.org/
A conclusion is simply the place where you got tired of thinking...

[Tim Chase]

>I have to search for a string on a big file. Once this string

>is found, I would need to get the number of the line in which
the string is located on the file. Do you know how if this is
possible to do in python ?

This should be reasonable:

>>>for num, line in enumerate(open( "/python25/readme.txt")):

if "Guido" in line:
print "Found Guido on line", num
break
Found Guido on line 1296

Just a small caveat here: enumerate() is zero-based, so you may
actually want add one to the resulting number:

s = "Guido"
for num, line in enumerate(open( "file.txt") ):
if s in line:
print "Found %s on line %i" % (s, num + 1)
break # optionally stop looking

Or one could use a tool made for the job:

grep -n Guido file.txt

or if you only want the first match:

sed -n '/Guido/{=;p;q}' file.txt

-tkc