在 Python 中的文本文件中的特定位置编辑特定行

Question

I have two variables x1=123.12 and y1=123.45 which holds user entered values .Now I have a text file in which I have to change current 245.42 and 130.32 with the variable x1 and y1 which holds user entered values.So how can I modify text file in python?

#text file:

var char12
name andy jordan
home illino

w1 345 3456 
p1 346 2123
addmoney 245.42
netmoney 130.32

Answer 1

Simply open the existing file and read the lines. Assuming that you want to replace the values that always follow 'addmoney' and 'netmoney', you can locate those lines and use re.sub() to substitute the values into those lines. Keep in mind that you can't simply overwrite text files in-place, so you store the modified lines and then recreate a new file at the end, like so:

x1 = 123.12
y1 = 123.45

import re

with open('mytextfile.txt', 'r') as f:
    lines = f.readlines()

    for i, l in enumerate(lines):

        if l.startswith('addmoney'):
            lines[i] = re.sub(r'[0-9.]+', str(x1), lines[i])
        elif l.startswith('netmoney'):
            lines[i] = re.sub(r'[0-9.]+', str(y1), lines[i])

out = open('modifiedtextfile.txt', 'w'); out.writelines(lines); out.close()