Apply a set of changes in grep -n format to a file

apply_grep_script.py

"""
Given a set of file names, line numbers, and lines of text in `grep -n` format,
update the file with altered text.

Suppose you have added a bunch of lines of code to your code base that have double
quotes when it is your company practice to use single quotes. When you are cleaning
up your code for a pull-request, you find all the changes with double quotes,
drop extraneous lines, change all the double quotes to single quotes in the
grep output, and use this python code to apply changes to your files.

Sort of like this:

```
$ grep  -n '"' $(git diff --name-only HEAD~2 | grep -v '.csv') > a
$ sed -i -e '/"""/d' a
$ sed -i "s/\"/'/g" a
$ python apply_grep_script.py a
```
"""

from itertools import groupby
import re
from operator import itemgetter

line_re = re.compile(r"""
    ^(?P<filename>[^:]+)
    :
    (?P<lineno>[^:]+)
    :
    (?P<rest>.*)$
""", re.VERBOSE)


def main(script):
    with open(script) as handle:
        lines = [line.rstrip() for line in handle]
    matches = (line_re.match(line) for line in lines)
    groupdict_iter = (
        m.groupdict()
        for m in matches
    )
    actions = [
        (g['filename'], int(g['lineno']) - 1, g['rest'])
        for g in groupdict_iter
    ]
    for k, g in groupby(actions, itemgetter(0)):
        # Read file
        with open(k) as handle:
            lines = [line.rstrip() for line in handle]
        print("Processing {0}: {1} lines".format(k, len(lines)))
        # Perform replacements
        for _, lineno, replacement in g:
            lines[lineno] = replacement
        # Write file
        with open(k, "w") as handle:
            handle.write("\n".join(lines) + "\n")


if __name__ == '__main__':
    import sys
    for script in sys.argv[1:]:
        main(script)