python替换文本文件中的单词而无需逐行

Question

I have a text file, say:

This is a text document
written in notepad

I want to replace 'document' with the word 'file' and 'notepad' with the word 'Notepad' and then I want to save / override the file. Now, without going line by line, because I know I can do

wordReplacements = {'document':'file', 'notepad':'Notepad'}
contents = open(filePath, 'r')
for line in contents:
    for key, value in wordReplacements.iteritems():
        line = line.replace(key, value)
contents.close()

but is there a way to do it without going line by line? Note: I am using python 2.7.

Answer 1

with open(sys.argv[1]) as f:
  words = f.read().replace("foo", "bar")

with open(sys.argv[1], "wb") as f:
  f.write(words)

Answer 2

Quoting from the docs ,

For reading lines from a file, you can loop over the file object. This is memory efficient, fast, and leads to simple code

So, I were you, I would have done it like this

import os
wordReplacements = {'document':'file', 'notepad':'Notepad'}

def transform_line(line):
    for key, value in wordReplacements.iteritems():
        line = line.replace(key, value)
    return line

with open("Output.txt", "w") as output_file, open("Input.txt") as input_file:
    for line in input_file:
        output_file.write(transform_line(line))

os.rename("Output.txt", "Input.txt")

If you prefer one-liners, you replace the with part with this

with open("Output.txt", "w") as output_file, open("Input.txt") as input_file:
    output_file.write("".join(transform_line(line) for line in input_file))

If memory is not a problem and you still want not to iterate over the file object, you can have the contents of the entire file moved to memory and then replace it there

import re
with open("Input.txt") as open_file:
    data = open_file.read()
for key, value in wordReplacements.iteritems():
    data = re.sub(key, value, data)
with open("Input.txt", "wb") as open_file:
    open_file.write(data)

Answer 3

With similar code,it's also possible to use re.sub method available in the re module to substitute based on the regular expression. However, using this method would require traversing the file content N times if you need to replace N patterns.