Generalize Your Substring Check

00:00 In this lesson, you’ll learn how to generalize your check by removing case sensitivity.

00:07 Previously you’ve worked with this text. It’s just a short text that contains the word secret a couple of times in different capitalizations, and you checked for the lowercase version by saying "secret" in text, and Python returned True for that.

00:24 This really just looked for a lowercase "secret" in that text, and because there is one, you got a True. Python found the substring.

00:34 But you need to keep in mind that strings in Python are case sensitive. So when you write "secret" == "SECRET", then Python returns False.

00:46 That’s because the lowercase letters and uppercase letters are different characters. So for Python, a lowercase "s" is distinct from an uppercase "S" in the same way that, for example, a lowercase "s" and a lowercase "x" are different.

00:59 So even though this is the same word for us as humans, it’s not the same string for the computer, which is why it returns False, which means that if you were looking for a substring and it does occur in your text, but only with a specific capitalization, then you are going to get False back from Python, even though for you as a human, the word that you’re looking for is actually in the text. For example, if I look for "sEcReT" in what I call SpongeBob case,

01:37 Python is going to return False because that specific capitalization of the word secret doesn’t appear in the text. So what you want to do to avoid this is just make sure that both the text and the substring have the same capitalization.

01:55 So for example, the text contains the word this, and the word this here is capitalized, so it starts with an uppercase T. Now if I were to look for "this" in text, then Python is going to return False.

02:12 But what I can do to make sure that both the substring as well as the string that I’m searching in are lowercase, is to say "this"—keep this one lowercase—and then say in text.lower().

02:25 So I’m calling the .lower() string method on the text string. This is going to lowercase all of the characters in there, and therefore my check whether the substring "this" is inside of the lowercase version of text is going to return True.

02:44 Let me show you what text.lower() does …

02:49 got to print it out.

02:54 As you can see, this is the same text as before, but all the words are in lowercase. So I will assign this to a new variable …

03:07 and for the rest of the tutorial, we are going to continue working with this text that is all lowercase, because that avoids any sort of issues that might come from just capitalization being off.

03:19 And now as long as you keep your substring also lowercase, then you’ll be able to always make sure that the word that you’re looking for also exists in the string.

03:32 Making sure that the capitalization of the substring and the string that you’re searching in are the same is going to help to make sure that you’re not accidentally not getting a match even though the word is inside of the string that you’re searching in.

03:54 And now that you know how you can find a substring in a string and how you can generalize the search a bit more, in the next lesson, you’ll take a look how you can learn a little bit more about the substring that Python identified.