python : replace mutiple words in a file

Question

I have a file apple.py ,it has words apple and Apple . And there is a blank file pear.py .

I want to read the content of apple.py and write it into pear.py ,and modify
apple to pear , Apple to Pear .

I do it like this:

def modify_city():
    with open('city.py', 'r+') as f:
        read_data = f.read()
    with open('beijing', 'w') as f:
        f.write(read_data.replace('city', 'beijing'))  #it works
        f.write(read_data.replace('City', 'Beijing'))  #it doesn't work

Question:
In the code,the first replace() works, but the second replace() doesn't work.what should I do?

Answer 1

You're writing the whole of read_data to the file twice.

read_data = read_data.replace('city','beijing')
read_data = read_data.replace('City','Beijing')
f.write(read_data)

Answer 2

The reasons why your code does not work is:

1. You write whole data to file twice.

2. str.replace() returns string with replace done, not changes the original string. By doing

    f.write(read_data.replace('city', 'beijing')) 

   first time, you print to file read_data with replaced 'city' and 'beijing' but you do not save changes to read_data . The second time when you do

    f.write(read_data.replace('City', 'Beijing')) 

   the previous replace isn't saved, thus resulting in replacing the original string.

This being said, you have two options:

def modify_city():
    with open('city.py', 'r+') as f:
        read_data = f.read()
    with open('beijing.py', 'w') as f:
        f.write(read_data.replace('city', 'beijing').replace('City', 'Beijing'))

or

def modify_city():
    with open('city.py', 'r+') as f:
        read_data = f.read()
    read_data = read_data.replace('city', 'beijing')
    read_data = read_data.replace('City', 'Beijing')
    with open('beijing.py', 'w') as f:
        f.write(read_data)