Simple Line Extractor

This program needs to support large text files (around a million lines at times). I believe Python would be the best language for this. Below I will explain what I need: [login to view URL] = A big file that has many random usernames Small example of [login to view URL]: SquirrelDan john3735 smalljohn 55john736 Randomu367 4384Robert robertbobby [login to view URL] = Certain names that I want to extract Small example of [login to view URL]: john squirrel [login to view URL] = Where the output goes It would search the file "[login to view URL]" for all the wanted names based on what I put into "[login to view URL]". THEN it would add a colon with the wanted name after it and then another with a "1" at the end. So based on the small examples above, it would search each line for "john" and "squirrel". The [login to view URL] would be: SquirrelDan:squirrel SquirrelDan:squirrel1 john3735:john john3735:john1 smalljohn:john smalljohn:john1 55john736:john 55john736:john1 So to explain again, it searches every line for the wanted names from "[login to view URL]" (NOT CASE SENSITIVE PLEASE), then it outputs it as I showed above, it will take the name from "[login to view URL]" then add a colon, then add the wanted name from "[login to view URL]" then do this again but add a "1" at the end. Needs to run on windows. Thank you! And please let me know any questions :)