Intermediate Python

Practice: Converting Between Types

Intermediate Python

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Nina walks through the practice segment.


Transcript from the "Practice: Converting Between Types" Lesson

>> Nina Zakharenko: Okay, let's go through our converting between types exercise.
>> Nina Zakharenko: So converting between strings and numbers, I can make a new string like this, right? Or, if I wanted to pas a number into, if I wanted to quickly convert an integer in to a string, I can pass it into the str function.

>> Nina Zakharenko: You might come across an error that looks like something like this. Let's say I wanted to print out,
>> Nina Zakharenko: Today is the, and then I wanna say, it's the 30th. So I put 30. And I'll get an error, TypeError, that says, you can only concatenate string not int, right?

So if you want to concatenate these two strings, you could wrap this number in that str call and that error will go away.
>> Nina Zakharenko: Okay, so if I check the type of str, 100, we know that it's str. If I check the type, if I pass a string into int, here, we know that it would be an int.

Again, if I pass the string into int, it'll come back with the integer.
>> Nina Zakharenko: We can also do this for floating point numbers.
>> Nina Zakharenko: And that will come back with the floating point number. Now, converting between lists and strings,
>> Nina Zakharenko: As I mentioned in Introduction to Python, a string is actually just kind of considered a list or a sequence of characters.

So converting back and forth is pretty easy. Let's say I had a variable here called greeting and the value is hello. I can pass that greeting into a list. What will I see?
>> Nina Zakharenko: What will the type of this be?
>> Speaker 2: List.
>> Nina Zakharenko: It'll be a list. And how many items will it have in it?

>> Speaker 2: Five [INAUDIBLE].
>> Nina Zakharenko: Five items, that's right.
>> Nina Zakharenko: So easy peasy. Let's say I wanted to undo what I just did. How do I take a list of characters and smush them back into one string?
>> Speaker 2: Join.
>> Nina Zakharenko: Join, yes. There's no smush method, it's just join. Okay, so if I wanted to combine them back and separate them by commas, I could call join.

>> Nina Zakharenko: If I didn’t make a variable for this list that I just made, I can pass this whole thing into this join method.
>> Nina Zakharenko: Or I could say,
>> Nina Zakharenko: That my characters were a list of my greeting, right? So that's just kind of the same thing. If I wanted to combine all these characters back without a delimiter, I could just join on the empty string.

>> Nina Zakharenko: And that gets us back to where we started.
>> Nina Zakharenko: To split up values in a string, in a comma separated value list like you might see, we can say csv_row = "the,quick,brown,fox". And what method would we need to call to make this a list of items?

>> Nina Zakharenko: Not quite, right?
>> Speaker 2: Split.
>> Nina Zakharenko: Yeah, we'll need to call split.
>> Nina Zakharenko: So with split, we call it on the the string that we're taking action on.
>> Nina Zakharenko: But with join, what do we call the join method on?
>> Speaker 2: The string.
>> Nina Zakharenko: The string, which string?
>> Speaker 2: Delimiter.

>> Nina Zakharenko: The delimiter string, that's exactly right. So, this kinda stuff all make sense?
>> Nina Zakharenko: There's one other, well, I'll come back it, I'll cover it later, but,
>> Nina Zakharenko: I showed you yesterday how if you had a list with some duplicates in it, let's say I had a list of names.

And you can type your own names here. Maybe we have Bob. We have some folks in the class. So we have a Jeff, and we have Madeline, and then we have another Nina, right? So whichever list you make just insert a duplicate. If I wanted to quickly de-duplicate this list of names, what data structure could I use?

>> Speaker 2: Set.
>> Nina Zakharenko: A set, right. A set cannot contain duplicates. So just like I was converting between the other types, I can say set, pass in my list of names, now the duplicates are gone. If I wanted to, I can convert those back into a list. If I wanted to sort it, I could pass the set into the sorted method.

What comes back from sorted, what type?
>> Speaker 2: A list.
>> Nina Zakharenko: It's a list, right? Because lists have order, sets do not. Okay, so it's super easy to convert back and forth. This will be really handy as you go through your Python journey.

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