How to replace string in multiple files in the folder? - python-2.7

Question

I m trying to read two files and replace content of one file with content of other file in files present in folder which also has sub directories.
But its tell sub process not defined.
i'm new to python and shell script can anybody help me with this please?
import os
import sys
import os.path
f = open ( "file1.txt",'r')
g = open ( "file2.txt",'r')
text1=f.readlines()
text2=g.readlines()
i = 0;
for line in text1:
l = line.replace("\r\n", "")
t = text2[i].replace("\r\n", "")
args = "find . -name *.tml"
Path = subprocess.Popen( args , shell=True )
os.system(" sed -r -i 's/" + l + "/" + t + "/g' " + Path)
i = i + 1;

Answer 1

To specifically address your actual error, you need to import the subprocess module as you are making use of it (oddly) in your code:
import subprocess
After that, you will find more problems. I will try and keep it as simple as possible with my suggestions. Code first, then I will break it down. Keep in mind, there are more robust ways to accomplish this task. But I am doing my best to keep in mind your experience level and making it make your current approach as closely as possible.
import subprocess
import sys
# 1
results = subprocess.Popen("find . -name '*.tml'",
shell=True, stdout=subprocess.PIPE)
if results.wait() != 0:
print "error trying to find tml files"
sys.exit(1)
# 2
tml_files = []
for tml in results.stdout:
tml_files.append(tml.strip())
if not tml_files:
print "no tml files found"
sys.exit(0)
tml_string = " ".join(tml_files)
# 3
with open ("file1.txt") as f, open("file2.txt") as g:
while True:
# 4
f_line = f.readline()
if not f_line:
break
g_line = g.readline()
if not g_line:
break
f_line = f_line.strip()
g_line = g_line.strip()
if not f_line or not g_line:
continue
# 5
cmd = "sed -i -e 's/%s/%s/g' %s" % \
(f_line.strip(), g_line.strip(), tml_string)
ret = subprocess.Popen(cmd, shell=True).wait()
if ret != 0:
print "error doing string replacement"
sys.exit(1)
You do not need to read in your entire files at once. If they are large this could be a lot of memory. You can consume a line at a time, and you can also make use of what is called "context managers" when you open the files. This will ensure they close properly no matter what happens:
We start with a subprocess command that is run only once to find all your .tml files. Your version had the same command being run multiple times. If the search path is the same, then we only need it once. This checks the exit code of the command and quits if it failed.
We loop over stdout on the subprocess command, and add the stripped lines to a list. This is a more robust way of your replace("\r\n"). It removes whitespace. A "list comprehension" would be better suited here (down the line). If we didn't find any tml files, then we have no work to do, so we exit. Otherwise, we join them together in a space-separated string to be suitable for our command later.
This is called "context managers". You can open the file in a way that no matter what they will be closed properly. The file is open for the length of the context within that code block. We are going to loop forever, and break when appropriate.
We pull a line, one at a time, from each file. If either line is blank, we reached the end of the file and cannot do any more work, so we break out. We then strip the newlines, and if either string is empty (blank line) we still can't do any work, but we just continue to the next available line.
A modified version of your sed command. We construct the command string on each loop for the source and replacement strings, and tack on the tml file string. Bear in mind this is a very naive approach to the replacement. It really expects your replacement strings to be safe characters and not break the s///g sed format. But we run that with another subprocess command. The wait() simply waits for the return code, and we check it for an error. This approach replaces your os.system() version.
Hope this helps. Eventually you can improve this to do more checking and safe operations.