如何在python中搜索和替换文本文件的多个值？

Question

My data:

1 255 59 0 1 255 0 1 1 0 4 0 5 

0 1 255 1 253 0 90 1 1 0 2 0 233

I'm new to python and I need to replace all value in text file by use conditions:

1. If value in line = 255, Replace as 1

2. If value in line < 255 (254, 253, 252...), Replace as 0

So, My target data is:

1 1 0 0 1 1 0 1 1 0 0 0 0 

0 1 1 1 0 0 0 1 1 0 0 0 0

How can I solve this problem?

Actually, I tried to fix it but doesn't work with my data.

This is my code:

f1 = open('20130103.txt','r')
f2 = open('20130103_2.txt','w')
count = 255
for line in f1:
    line = line.replace('255','1')
    count = count-1
    line = line.replace('%d'%(count), '0')
    f2.write(line)
f1.close()
f2.close()

And result is:

1 1 59 0 1 1 0 1 1 0 4 0 5 
0 1 1 1 0 0 90 1 1 0 2 0 233

Answer 1

The eye catcher here is the number 255 , for which you would want to display 1 , which clearly indicates, you are only interested in the 8th bi t. The only case which looks strange is how your o/p not conforming with your requirement, does not manipulate 1 in which case, you have to leave it out of your transformation

If I have to trust your requirement

>>> with open("test.in") as fin, open("test.out","w") as fout:
    for line in fin:
        line = (e >> 7 for e in map(int, line.split()))
        fout.write(''.join(map(str, line)))
        fout.write('\n')

If I have to trust your data

>>> with open("test.in") as fin, open("test.out","w") as fout:
    for line in fin:
        line = (e >> 7 if e != 1  else 1 for e in map(int, line.split()))
        fout.write(''.join(map(str, line)))
        fout.write('\n')

Another alternate view to this problem.

>>> with open("test.in") as fin, open("test.out","w") as fout:
    for line in fin:
        line = (e / 255 if e != 1  else 1 for e in map(int, line.split()))
        fout.write(''.join(map(str, line)))
        fout.write('\n')

Answer 2

You could do something like this:

with open('20130103.txt', 'r') as f1, open('20130103_2.txt', 'w') as f2:
    for line in f1:
        values = line.split()
        new_values = ' '.join('1' if value == '255' else '0' for value in values)

        f2.write(new_values + '\n')

• line.split() splits the line into chunks. 'a b'.split() == ['a', 'b']
• '1' if value == '255' else '0' for value in values is a generator that just outputs '1' or '0' , depending on the value of an item in your list of values.
• ' '.join() joins together the values in the list (or generator, in this case) with a space.

Answer 3

Here's an example of how you can pass re.sub a function -- instead of a replace string -- to gain really fine control over how replacements are done:

import re
lines = ['1 255 59 0 1 255 0 1 1 0 4 0 5',
     '0 1 255 1 253 0 90 1 1 0 2 0 233']
def do_replace(match):
    number = int(match.group(0))
    if number == 0 or number == 1:
        return str(number)
    elif number == 255:
        return '1'
    elif number < 255:
        return '0'
    else:
        raise ValueError
for line in lines:
    print re.sub(r'\d+', do_replace, line)

prints:

1 1 0 0 1 1 0 1 1 0 0 0 0
0 1 1 1 0 0 0 1 1 0 0 0 0