Read certain part of string from file

Question

Trying python after a very long time now.

I have a file that has a line:

My_NUMBER                 =  24

I want to extract this number ( here I have assumed 24 but this is something I want to extract based on My_NUMBER.In my python code I am able to read the line

with open(filename) as f: lines = f.read().splitlines()

for line in lines:
    if line.startswith(' My_NUMBER                 ='):
        line=(line.rsplit(' ', 1)[0])
        num= line.rsplit('=',1)[1].split("=")[0]
        num = num.strip(" ")
        print num

However this does print blank output and not the number. Can anyone commet in case I am doing anything obviously wrong here?

what do you think this line `line=(line.rsplit(' ', 1)[0])` is doing? — SilentGhost, Oct 31 '12 at 12:44

enrico.bacis · Answer 1 · 2012-10-31T13:20:16.257

3

This is the perfect job for a regex:

import re
text = open(filename).read()
print re.search("^\s*My_NUMBER\s*=\s*(\d*)\s*$", text, re.MULTILINE).group(1)

edited Oct 31 '12 at 13:20

answered Oct 31 '12 at 12:45

enrico.bacis

30,497
10
86
115

1

I would suggest using `(\d*)` or `(\d+)` instead of `(.*)` – sloth Oct 31 '12 at 12:47
Perfect, I thought he didn't know what was after the equal sign. Thanks – enrico.bacis Oct 31 '12 at 12:50
there could be a whitespace after the number. – jfs Oct 31 '12 at 13:12

Tim · Answer 2 · 2012-10-31T13:13:57.017

2

I'd go with something like this

with open(filename) as f:
    for line in f:
        line = line.replace(' ', '')
        if line.startswith('My_NUMBER'):
            number = line.partition('=')[2]
            print number

edited Oct 31 '12 at 13:13

answered Oct 31 '12 at 12:46

Tim

11,710
4
42
43

2

Why has this been downvoted? It might not be perfect, but it's not as ghastly as all this regex answers. – SilentGhost Oct 31 '12 at 12:54
This will remove whitespace from the unknown value after the `=` - better to use `.strip()` on the `str.partition`'d value – dbr Oct 31 '12 at 13:09
could you add [code showing the OP how to read a file line-by-line](http://ideone.com/66bnWb) otherwise if the whole file is already in memory then a regex would work fine there is no need to iterate line by line – jfs Oct 31 '12 at 13:10
@dbr: there is no whitespace in a number – jfs Oct 31 '12 at 13:10

score 0 · Answer 3 · answered Oct 31 '12 at 12:44

Might be better off using regex

import re

txt='My_NUMBER                 =  24'

re1='.*?'   # Non-greedy match on filler
re2='(\\d+)'    # Integer Number 1

rg = re.compile(re1+re2,re.IGNORECASE|re.DOTALL)
m = rg.search(txt)
if m:
    int1=m.group(1)
    print "("+int1+")"+"\n"

From here: http://txt2re.com/index-python.php3?s=My_NUMBER%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20=%20%2024&4

score 0 · Answer 4 · answered Oct 31 '12 at 12:44

try something like this:

In [49]: with open("data1.txt") as f:
   ....:     for line in f:
   ....:         if line.strip():           #if line is not an empty line
   ....:             if "My_NUMBER" in line:
   ....:                 num=line.split("=")[-1] # split line at "=" and 
                                                 # return the last element
   ....:                 print num
   ....:                 
   ....:                 
  24

iurisilvio · Accepted Answer · 2012-10-31T17:14:05.537

0

for line in lines:
    if line.startswith(' My_NUMBER                 ='):
        num = line.split('=')[-1].strip()
        print num

edited Oct 31 '12 at 17:14

answered Oct 31 '12 at 12:46

iurisilvio

4,868
1
30
36

5

This indentation looks funny to me. I'm pretty sure you need to move `lines = f.read().splitlines()`. Also, if you're going to do that, you might as well get rid of it all together and just iterate over the file: `for line in f:` instead of `for line in lines:` – mgilson Oct 31 '12 at 12:53
@mgilson yeap, that was completely wrong. Sorry. At least, it helped the OP. – iurisilvio Oct 31 '12 at 17:16

score 0 · Answer 6 · answered Oct 31 '12 at 12:46

0

import re

exp = re.compile(r'My_NUMBER *= *(\d*)')
with open('infile.txt','r') as f:
    for line in f:
        a = exp.match(line)
        if a:
            print a.groups()[0]

Untested, but should work

answered Oct 31 '12 at 12:46

Matt

3,651
3
16
35

dbr · Answer 7 · 2012-10-31T13:06:52.387

0

The tidiest way, I would say, is to loop over each line, split based on =, then check if the value before the = is MY_NUMBER

The str.partition function is good for this (it's similar to split, but always returns 3 chunks). Also using str.strip means you don't need to worry about the whitespace

with open(filename) as f:
    lines = f.readlines()

for line in lines:
    key, eq, value = line.partition("=")
    if key.strip() == "MY_NUMBER":
        num = value.strip()
        print num

edited Oct 31 '12 at 13:06

answered Oct 31 '12 at 12:55

dbr

165,801
69
278
343

1

Besides being nearly identical to Tim's answer. Why, oh why, are you doing `.read().splitlines()`? – SilentGhost Oct 31 '12 at 12:56
@SilentGhost it was copy-pasted from the original answer, edited (Tim's answer is also not identical, depending on the value after the `=`, commented on this answer) – dbr Oct 31 '12 at 13:07

Read certain part of string from file

7 Answers7