python - Pythonで定義せずに関数が呼び出される方法

Question

プログラムは次のとおりです。

import sys

def IndexSearchString():
    '''

    This function search a string in a password file through index and gives the result.

    :return: none
    :return type: none 
    :author: Neeraj    

    '''
    fieldindex = int(sys.argv[1])-1
    stringsrch = sys.argv[2]

    file_name = open("passwd", "r")

    for store_file in file_name:
        temp = store_file.split(":")
        search = temp[fieldindex]
        #print search 

        if stringsrch in search:
            print store_file
            #print sys.stdout.write(store_file)   
            return

#IndexSearchString()