如何使用Python替换本文中的冒号？

Question

I have a file which looks like

1::12::33::1555
1::412::1245::23444

and so on. I need to get rid of the last argument, and replace the colons with commas. I have tried:

  myfile = open('words.txt', 'r')
  content = myfile.read()
  content = re.sub(r'(.+)::(.+)::(.+)::(.+)', "\1,\2,\3", content)
  myfile = open('words.txt', 'w')
  myfile.write(content)   
  # Close the file
  myfile.close()

but the back reference doesn't work, and I just end up with a file with commas..

What I'm hoping to achieve is:

1,12,33
1,412,1245

Answer 1

Backreferences will only be interpolated with a raw string.

re.sub(r'(.+)::(.+)::(.+)::(.+)', r"\1,\2,\3", content)

You could also do this using purely strings/lists

"\n".join([",".join(y.split('::')[:-1]) for y in content.split("\n")])

Answer 2

You could use the CSV library like so (embedding the CSV for simplicity):

import StringIO
import csv

t = """1::12::33::1555
1::412::1245::23444"""

f = StringIO.StringIO(t)
reader = csv.reader(f, delimiter=':')
for row in reader:
    print ",".join(row[0:-1:2])

This outputs:

1,12,33
1,412,1245

Answer 3

Can you just use simple string functions?

line = '1::412::1245::23444'
s = s.replace('::',',')
# content stored in a list
content = s.split(',')[:-1]

Answer 4

In Python 2.6:

with open('words.txt', 'r') as in_file:
    with open('words_out.txt', 'w') as out_file:
        for line in in_file:
            new_line = ','.join(line.split('::')[:-1]) + ','
            out_file.write(new_line)

In Python 2.7 >

with open('words.txt', 'r') as in_file, open('words_out.txt', 'w') as out_file:
    for line in in_file:
        new_line = ','.join(line.split('::')[:-1]) + ','
        out_file.write(new_line)

Answer 5

This would give you the string you need:

line = '1::412::1245::23444'
line_list = line.split('::')
new_line = ','.join(line_list[:-1])

print new_line
>> 1,412,1245

Answer 6

It doesn't look like you truly need regex for this. What I would do is split the line using :: as a delimiter, then drop the last item and re-insert commas.

myfile = open('words.txt', 'r')
content = myfile.read()
numbers = [int(s) for s in content.split("::")]     #get a list of numbers from the string
numbers = numbers[0:-1]                             #drop last number
content = "".join([str(n) + ",," for n in numbers]) #coalesce numbers back to string
myfile = open('words.txt', 'w')
myfile.write(content)   
myfile.close()