Parse git unified diff files in python3

patch.py

import re

class Patch:
    """ Parses and encapsulates a git unified diff/patch file. """

    # See: https://stackoverflow.com/questions/987372/what-is-the-format-of-a-patch-file
    # Chunk headers look like: @@ -4,9 +4,12 @@. The following regex parses them

    ptn = (
        r"@@ -(?P<old_start>\d+),"  # Where the chunk begins in the old file
        r"(?P<old_n_lines>\d+) "  # Number of lines in the chunk in the old file
        r"\+(?P<new_start>\d+),"  # Where the chunk begins in the new file
        r"(?P<new_n_lines>\d+) "  # Number of lines in the chunk in the new file
        "@@(?P<chunk_content>(.(?!@@))+)"  # String contents of the chunk
    )

    self.chunks = []

    def __init__(self, patchfile_content: str):
        for match in re.finditer(self.ptn, patchfile_content, re.DOTALL):
            chunk = match.groupdict()

            # These parts of the patch chunk header are integer line numbers
            for numeric_part in [
                "old_start",
                "old_n_lines",
                "new_start",
                "new_n_lines",
            ]:
                chunk[numeric_part] = int(chunk[numeric_part])

            self.chunks.append(chunk)