Question

In the below code i am trying to replace the contents of a file which has the following content in it.
hellohello world and the string hellohello should be replaced by hello and be wrote back to the file.Ho to go about this

  #!/usr/bin/python
  import os

  new_file_list=[]
  all_files=os.listdir("/tmp")
  for ff in all_files:
     if ff.endswith(".txt"):
        new_file_list.append(ff)

  for files in new_file_list:
     if files == "a.txt":
       print "======================================="
       file_name="/tmp/"+str(files)
       print file_name
       f=open(file_name ,"rw")
       while True:
         print "======================================="
         for line in f.readline():
            print line
            print "======================================="
            f.write(line.replace("hellohello","hello"))
            print line
         else:
            break
       for line in f.readline():
         print line

  f.close()

Answer 1

You can use fileinput module to replace string in a file in place (without opening two files or opening the same file twice or loading entire text file into memory in your code).

#!/usr/bin/python
import os
import fileinput

new_file_list=[]
all_files=os.listdir("/tmp")
for ff in all_files:
 if ff.endswith(".txt"):
    new_file_list.append(ff)

for files in new_file_list:
 print files
 if files == "a.txt":
   print "======================================="
   file_name="/tmp/"+str(files)
   print file_name

   f = fileinput.FileInput(file_name, inplace=1)

   print "======================================="
   for line in f:
        line = line.replace("hellohello","hello")
        print line,
   f.close()