replacing text in a file with Python

Question

I m new to Python  I want to be able to open a file and replace every instance of certain words with a given replacement via Python   as an example say replace every word  zero  with  0    temp  with  bob   and say  garbage  with  nothing    I had first started to use this   for line in fileinput input fin           fout write line replace  zero    0            fout write line replace  temp   bob            fout write line replace  garbage   nothing      but I don t think this is an even remotely correct way to do this   I then thought about doing if statements to check if the line contains these items and if it does  then replace which one the line contains  but from what I know of Python this also isn t truly an ideal solution   I would love to know what the best way to do this   Thanks ahead of time

User · Answer

This is a short and simple example I just used:

If:

fp = open("file.txt", "w")

Then:

fp.write(line.replace('is', 'now'))
// "This is me" becomes "This now me"

Not:

line.replace('is', 'now')
fp.write(line)
// "This is me" not changed while writing

User · Answer

Reading from standard input  write  code py  as follows   import sys  rep     zero   0    temp   bob    garbage   nothing    for line in sys stdin      for k  v in rep iteritems            line   line replace k  v      print line   Then  execute the script with redirection or piping  http   en wikipedia org wiki Redirection  computing    python code py  lt  infile  gt  outfile

User · Answer

If your file is short  or even not extremely long   you can use the following snippet to replace text in place     Replace variables in file with open  path to in-out-file    r    as f      content   f read       f seek 0      f truncate       f write content replace  replace this    with this

User · Answer

The essential way is   read    data   data replace   as often as you need and then write      If you read and write the whole data at once or in smaller parts is up to you  You should make it depend on the expected file size   read   can be replaced with the iteration over the file object

User · Answer

Faster way of writing it would be     in   open  path to input file   read   out   open  path to input file    w   replacements     zero   0    temp   bob    garbage   nothing   for i in replacements keys        in   in replace i  replacements i   out write in  out close   This eliminated a lot of the iterations that the other answers suggest  and will speed up the process for longer files

User · Answer

I might consider using a dict and re sub for something like this   import re repldict     zero   0    one   1    temp   bob   garage   nothing   def replfunc match       return repldict match group 0    regex   re compile     join re escape x  for x in repldict   with open  file txt   as fin  open  fout txt   w   as fout      for line in fin          fout write regex sub replfunc line     This has a slight advantage to replace in that it is a bit more robust to overlapping matches

User · Answer

This should do it  replacements     zero   0    temp   bob    garbage   nothing    with open  path to input file   as infile  open  path to output file    w   as outfile      for line in infile          for src  target in replacements iteritems                line   line replace src  target          outfile write line    EDIT  To address Eildosa s comment  if you wanted to do this without writing to another file  then you ll end up having to read your entire source file into memory   lines      with open  path to input file   as infile      for line in infile          for src  target in replacements iteritems                line   line replace src  target          lines append line  with open  path to input file    w   as outfile      for line in lines          outfile write line    Edit  If you are using Python 3 x  use replacements items   instead of replacements iteritems

[python] replacing text in a file with Python

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