如何在python 3.6中编辑多行文本文件？

Question

I'm new to coding (cumulative 2 weeks of learning). I'm using python 3.6. Currently I'm trying to read a file with text (copy.txt), edit it and write in another file (paste.txt).

Copy.txt looks like this:

  ;ROLE_NAME                                                     ;GRANTOR  
1 ;rolea                                                         ;SYS      
2 ;rolec                                                         ;SYSTEM   
3 ;roley                                                         ;_SYS_REPO
4 ;rolez                                                         ;_SYS_REPO

And I want the text to look like this in paste.txt (after formatting):

SYS
grant rolea to user

SYSTEM
grant rolec to user

_SYS_REPO
grant roley to user
grant rolez to user

What I've done by now - reading the file copy.txt, which is in the same dir as the script:

from os.path import abspath, exists

f_path = abspath("copy.txt")


if exists(f_path):
        with open(f_path) as f:
        print (f.read())

I don't have an idea how to make changes in each line. I was thinking about making a dictionary that takes two values and using f.split(';') to assign these values. Also I tought about counting the number of lines, and edit each one in loop, using this:

num_lines = sum(1 for line in f)

Could you give me some guidelines about the concept how the text should be formatted?

Disclaimer: I've read a lot of other posts, but couldn't find one helping me with my task.

Answer 1

You're on the right track about thinking of creating a dictionary. You could create a dictionary that maps grantors to a list of roles .

First, you need to read in the file, exactly like you have already done:

from os.path import abspath, exists

f_path = abspath("copy.txt")

if exists(f_path):
    with open(f_path) as f:
        lines = f.readlines()

lines is just a list of the lines in "copy.txt"

Then you need to create that dictionary:

role_dict = {}
for line in lines[1:]:
    split_line = line.split(';')
    role = split_line[1].strip()
    grantor = split_line[2].strip()
    if grantor in role_dict:
        role_dict[grantor].append(role)
    else:
        role_dict[grantor] = [role]

In the example you have given, role_dict would look like the following:

{'SYS': ['rolea'], 'SYSTEM': ['rolec'], '_SYS_REPO': ['roley', 'rolez']}

Finally, you just need to write it out in order:

with open('paste.txt', 'w') as f:
    for grantor in sorted(role_dict.keys()):
        roles = role_dict[grantor]
        f.write(grantor + '\n')
        for role in roles:
            f.write('grant {} to user\n'.format(role))
        f.write('\n')