how can I take an specific line in big file which has many similar lines, using python?

have different files with same name, in different directories. In these files there are lines which are almost equal, I would like to take out only the last line of these ones( there are more lines after it) and write it in another file.

So far what I have done:

#!/usr/bin/env python

import os

def cd_grep():
   for file in os.listdir("."):
     if os.path.isfile(file):
       for line in open开发者_如何学Go("graph.txt"):
                  if " 4.49" in line:                               
                       line_list=[line] 
   g = open('comparation','a') 
   g.write ("%s" % (line[0:4]))
   g.close()
os.chdir('4.294')
cd_grep()
os.chdir(os.pardir)
os.chdir('4.394')
cd_grep()
os.chdir(os.pardir)
os.chdir('4.494')
cd_grep()
os.chdir(os.pardir)
os.chdir('4.594')
cd_grep()
os.chdir(os.pardir)
os.chdir('4.694')
cd_grep()

I've created a list because I am gonna take only a specific information of the whole line.

Finally I got that this procedure only works for small files and only if the last line of the file contains the term I'm searching. For big files, I got this message ( inside the file, which I was hoping to get the line):

Voluntary context switches: 3403

Any idea or suggestion will be very appreciate.

Not sure about the error you are receiving (after your last edit).

I have tried to rewrite the code a bit, hope it gives you a result similar to what you need (WARNING: not tested).

with open ('comparation', 'a') as write_file:
  for path, dirs, files in os.walk(os.getcwd()):
    for filename in [f for f in files if f == "graph.txt"]:
      filepath = os.path.abspath(os.path.join(path, filename))
      with open(filepath) as f:
        for line in f:
          if " 4.49" in line:
            last = line
        write_file.write("File: %s, Line: %s\n" % (filepath, last[0:4]))        

I'm guessing you aren't closing your files.

def cd_grep():
    for file in os.listdir("."):
        if os.path.isfile(file):
           graph_file = open('graph.txt'):
           for line in graph_file:
               if " 4.49" in line:                               
                   line_list=[line] 
           graph_file.close()
    g = open('comparation','a') 
    g.write ("%s" % (line[0:4]))
    g.close()

Or much better use with to open (and always close) your files.

def cd_grep():
    for file in os.listdir("."):
        if os.path.isfile(file):
           with open('graph.txt') as graph_file:
               for line in graph_file:
                   if " 4.49" in line:                               
                       line_list=[line] 
    with open('comparation','a') as g:
        g.write ("%s" % (line[0:4]))