Replace words in a file
 

I need to read in a text file, replace selected words and write the changed text back out to a file. Is there an easy way with Python?

Re: Replace words in a file
 

there are several ways.
1) reading with for loop

o = open("output","a") #open for append

for line in open("file"):

   line = line.replace("someword","newword")

   o.write(line + "\n") 

o.close()

2) with while loop

f = open("file")

o = open("output","a")

while 1:

  line = f.readline()

  if not line: break

  line = line.replace("someword","newword")

  o.write(line + "\n")

o.close()

3) using regular expression and reading the whole file into memory

import re

o = open("output","w")

data = open("file").read()

o.write( re.sub("someword","newword",data)  )

o.close()

If you don't want to explicitly declare file handles for writing to output file, you can use fileinput module, to modify file in place

import fileinput

for line in fileinput.FileInput("file",inplace=1):

   line = line.replace("blah","blahblah")

   print line

Re: Replace words in a file
 

Thanks ghostdog!
I will have to play with those code ideas. I need to replace several different words in the text file.

Re: Replace words in a file
 

Here is an example, where the target and replacement words are in a dictionary. The Python module re is used to do the gruntwork ...

# read a text file, replace multiple words specified in a dictionary

# write the modified text back to a file

 

import re

 

def replace_words(text, word_dic):

    """

    take a text and replace words that match a key in a dictionary with

    the associated value, return the changed text

    """

    rc = re.compile('|'.join(map(re.escape, word_dic)))

    def translate(match):

        return word_dic[match.group(0)]

    return rc.sub(translate, text)

 

 

str1 = \

"""When we see a Space Shuttle sitting on its launch pad, there are two big

booster rockets attached to the sides of the main fuel tank. These are solid

rocket boosters, made by Thiokol at their factory in Utah. The engineers who

designed the solid rocket boosters might have preferred to make them a bit

fatter, but they had to be shipped by train from the factory to the launch

site.  The railroad line from the factory runs through a tunnel in the

mountains.  The boosters had to fit through that tunnel.  The tunnel is

slightly wider than the railroad track.  The width of the railroad track

came from the width of horse-drawn wagons in England, which were as wide

as two horses' behinds.  So, a major design feature of what is the world's

most advanced transportation system was determined over two thousand years

ago by the width of a horse's ass!

"""

 

test_file = "Mword1.txt"

# create a test file for this example

fout = open(test_file, "w")

fout.write(str1)

fout.close()

 

# read the file

fin = open(test_file, "r")

str2 = fin.read()

fin.close()

 

# the dictionary has target_word:replacement_word pairs

word_dic = {

'booster': 'rooster',

'rocket': 'pocket',

'solid': 'salted',

'tunnel': 'funnel',

'ship': 'slip'}

 

# call the function and get the changed text

str3 = replace_words(str2, word_dic)

 

# test

print str3

 

# write changed text back out

fout = open("Mword2.txt", "w")

fout.write(str3)

fout.close()

Re: Replace words in a file
 

Thanks again, the last code example will work for me. I will have to read up on the module re to digest it all.

Re: Replace words in a file
 

If i wanted to read the words to be replaced from another text file and then replace them wat modifications to the code would i have to make??