如何在文件中进行多行字符串搜索并获取python中的起始行，结束行信息？

Question

I want to search for multi-line string in a file in python. If there is a match, then I want to get the start line number, end line number, start column and end column number of the match. For example: in the below file ,

I want to match the below multi-line string:

pattern = """b'0100000001685c7c35aabe690cc99f947a8172ad075d4401448a212b9f26607d6ec5530915010000006a4730'
           b'440220337117278ee2fc7ae222ec1547b3a40fa39a05f91c1e19db60060541c4b3d6e4022020188e1d5d843c'"""

The result of the match should be as: start_line : 2, end_line = 3, start_column : 23 and end_column : 114

The start column is the index in that line where the first character is matched of the pattern and end column is the last index of the line where the last character is matched of the pattern. The end column is shown below:

I tried with the re package of python but it returns None as it could not find any match.

import re

pattern = """b'0100000001685c7c35aabe690cc99f947a8172ad075d4401448a212b9f26607d6ec5530915010000006a4730'
           b'440220337117278ee2fc7ae222ec1547b3a40fa39a05f91c1e19db60060541c4b3d6e4022020188e1d5d843c'"""
                       

with open("test.py") as f:

  content = f.read()

  print(re.search(pattern, content))

I can find the metadata of the location of the match of a single line strings in a file using

with open("test.py") as f:
  data = f.read()
  for n, line in enumerate(data):
    match_index = line.find(pattern)
    if match_index != -1:
      print("Start Line:", n + 1)
      print("End Line", n + 1)
      print("Start Column:", match_index)
      print("End Column:", match_index + len(pattern) + 1)
      break

But, I am struggling to make it work for multi-line strings. How can I match multi-line strings in a file and get the metadata of the location of the match in python?

Answer 1

You should use the re.MULTILINE flag to search multiple lines

import re
pattern = r"(c\nd)"
string = """
a
b
c
d
e
f
"""

match = re.search(pattern, string, flags=re.MULTILINE)
print(match)

To get the start line, you could count the newline characters as follows

start, stop = match.span()
start_line = string[:start].count('\n')

You could do the same for the end_line , or if you know how many lines is your pattern, you can just add this info to avoid counting twice.

To also get the start column, you can check the line itself, or a pure regex solution could also look line:

pattern = "(?:.*\n)*(\s*(c\s*\n\s*d)\s*)"
match = re.match(pattern, string, flags=re.MULTILINE)
start_column = match.start(2) - match.start(1)
start_line = string[:match.start(1)].count('\n')
print(start_line, start_column)

However, I think difflib could be more useful here.

Alternative Solution

Below, I got a more creative solution to your problem: You are interested in the row and column position of some sample text (not a pattern, but a fixed text) in a larger text. This problem reminds me a lot on image registration, see https://en.wikipedia.org/wiki/Digital_image_correlation_and_tracking for a short introduction or https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.correlate2d.html for a more sophisticated example.

import os
from itertools import zip_longest

import numpy as np

text = """Some Title
abc xyz ijk
  12345678
  abcdefgh
xxxxxxxxxxx
012345678
abcabcabc
yyyyyyyyyyy
"""
template = (
    "12345678",
    "abcdefgh"
)
moving = np.array([
    [ord(char) for char in line]
    for line in template
])
lines = text.split(os.linesep)
values = [
    [ord(char) for char in line]
    for line in lines
]
# use zip longest, to pad array with fill value
reference = np.array(list(zip_longest(*values, fillvalue=0))).T
windows = np.lib.stride_tricks.sliding_window_view(reference, moving.shape)
# get a distance matrix
distance = np.linalg.norm(windows - moving, axis=(2, 3))
# find minimum and retrun index location
row, column = np.unravel_index(np.argmin(distance), distance.shape)
print(row, column)