在python中匹配文本后打印第N行

Question

I am trying to print 13th line in a text file after the every search match. Means everytime a searching pattern is found in text file, it should print the next 13th line from the searching text found.

Code I am using now, prints only the current line where the search matches. Can anybody help me how to print the 13th line after each match.

import sys
import re
com=str(sys.argv[1])
with open("/tmp/sample.txt", 'r') as f:
    for line in f:
          if com in line:
            print (line)

Answer 1

The easiest way would be to read all lines at once, then search and print:

import sys
import re
com=str(sys.argv[1])
with open("/tmp/sample.txt", 'r') as f:
    lines = f.readlines()
    for index, line in enumerate(lines):
        if com in line:
            print lines[index+13]

Supposing, of course, that there still is a line to print 13 lines down... Otherwise, your could add:

        ....
        if com in line:
            try:
                print lines[index+13]
            except IndexError:
                pass  # or whatever you want to do.