1 00:00:00,000 --> 00:00:02,990 Let's take a look at how we can do search and replace using regular 2 00:00:03,000 --> 00:00:04,990 expressions in Python. 3 00:00:05,000 --> 00:00:13,990 Start by making a working copy of regex.py. Call it regex-working.py. 4 00:00:14,000 --> 00:00:18,990 We'll open our working copy and here we have our little script that searches for 5 00:00:19,000 --> 00:00:20,990 a particular pattern in a file. 6 00:00:21,000 --> 00:00:26,990 If we run this, you see it finds all the places where either Lenore or Nevermore 7 00:00:27,000 --> 00:00:30,990 is found in Edgar Allan Poe's "The Raven." 8 00:00:31,000 --> 00:00:34,990 So let's do a search and replace instead of just a plain search. 9 00:00:35,000 --> 00:00:40,990 Search and replace in Python is done with re.sub, so we'll change this re.search 10 00:00:41,000 --> 00:00:45,990 to re.sub and we'll use the same pattern there. 11 00:00:46,000 --> 00:00:50,990 And we put in our replacement pattern here. We'll just replace it with some hash 12 00:00:51,000 --> 00:00:58,990 marks and we are going to turn this if into just a print and we'll at the end of that, 13 00:00:59,000 --> 00:01:04,990 we'll put the end= blank like that and we don't need this anymore. 14 00:01:05,000 --> 00:01:11,990 So now, we have re.sub and sub is the search and replace in the regular 15 00:01:12,000 --> 00:01:14,990 expression package in Python and the first argument is the regular 16 00:01:15,000 --> 00:01:16,990 expression pattern itself. 17 00:01:17,000 --> 00:01:20,990 The second argument is what to replace it with when it's found, and then the 18 00:01:21,000 --> 00:01:23,990 string to replace it from. 19 00:01:24,000 --> 00:01:27,990 Now in this case, this will go ahead and print the string even if it doesn't 20 00:01:28,000 --> 00:01:28,990 find any replacement. 21 00:01:29,000 --> 00:01:30,990 So it will print the string either way. 22 00:01:31,000 --> 00:01:34,990 So we'll get the entire file with just those lines replaced. 23 00:01:35,000 --> 00:01:38,990 So I'll save this and run it and we'll go ahead and maximize this and we can see 24 00:01:39,000 --> 00:01:43,990 these places where the hash marks are found. These are places where it found 25 00:01:44,000 --> 00:01:49,990 either Lenore or Nevermore. 26 00:01:50,000 --> 00:01:53,990 So that's the simplest form of a search and replace in Python. 27 00:01:54,000 --> 00:01:56,990 Let's say though that we just want to print the lines where we actually found it 28 00:01:57,000 --> 00:02:00,990 and print those lines with that string replaced. 29 00:02:01,000 --> 00:02:04,990 So one easy way to do that is instead of putting the print here we can do a 30 00:02:05,000 --> 00:02:09,990 search here and get this results of the search with match, hence we use this 31 00:02:10,000 --> 00:02:14,990 search function, just how we learned to do it before. 32 00:02:15,000 --> 00:02:23,990 So search in line like that and then if match, because we only want those lines 33 00:02:24,000 --> 00:02:28,990 whether it's been a match, then we can do a simple string substitution, and 34 00:02:29,000 --> 00:02:40,990 print line and say end= blank like that and we can use the replace method in the 35 00:02:41,000 --> 00:02:43,990 line object itself. 36 00:02:44,000 --> 00:02:49,990 And we have our result in match and it's in the group method and what we replace 37 00:02:50,000 --> 00:02:51,990 it with is the hash marks. 38 00:02:52,000 --> 00:02:56,990 So this is actually doing the search and replace in two separate steps. 39 00:02:57,000 --> 00:03:01,990 The search is being done using the regular expressions and the result is in the match object. 40 00:03:02,000 --> 00:03:06,990 We can test the match object to see if it's true, then it will have a match and 41 00:03:07,000 --> 00:03:13,990 then we can use that match in the string replace method to do the replacement. 42 00:03:14,000 --> 00:03:18,990 So if we save this and run it, so now we get only those lines where the string 43 00:03:19,000 --> 00:03:22,990 was found and we have the replacement in those lines. 44 00:03:23,000 --> 00:03:25,990 So those are a couple of simple ways to use Python's regular expressions module 45 00:03:26,000 --> 00:03:36,000 to do search and replace.