Function Arguments

[00:00:00]
>> Nina Zakharenko: Okay, so we've talked about calling functions with and without arguments. And you also know how to store the returned value of a function, right? You just assign it to a variable just like anything else. Okay, let's talk about Function Arguments.
>> Nina Zakharenko: So let's say I have my add number function and it takes an x and a y and it returns, x + y.

[00:00:38]
If I can add numbers with 3 and 5, I'll get an 8. What if I call add numbers without passing in the second parameter? What kind of error do I get? Y'all have a rupple so y'all have the answers right under your fingertips.
>> Student: It's the argument?
>> Nina Zakharenko: That's right, so it’s a type error, that’s the class, see that right here.

[00:01:10]
It's missing one required positional argument, and helpfully it even tells us which one.
>> Nina Zakharenko: So any arguments defined this way are required. And it doesn't matter what order you pass them in, when you call them they're just gonna be x and y in order within the scope of the function.

[00:01:38]
>> Nina Zakharenko: Python also has key word arguments with default values. Which is really helpful, we can optionally pass in the argument if we want. If we don't want to, there is a default available for us. So let's say we have a function called say_greeting, and it takes a greeting and a name.

[00:02:02]
>> Nina Zakharenko: And we're gonna print out the f string of {greeting}, {name}.
>> Nina Zakharenko: Is everyone getting the hand of these f strings? Yeah, awesome, I thought so.
>> Nina Zakharenko: Okay, so I can call, say, greeting with hello and Nina. It'll print out Hello, Nina.
>> Nina Zakharenko: Let's say I didn't want to pass in Hello all the time.

[00:02:34]
Hello was be used most of the time by default when calling this function. But I wanted to have the option of changing my greeting if I wanted to.
>> Nina Zakharenko: So we're gonna make a new function.
>> Nina Zakharenko: We're going to call it say greeting. If I define those function in the rupple, just know that it will overwrite the other function I've defined here, and that's because they have the same name.

[00:03:05]
So now I'm going to take a name, right, cuz that's kind of the variable of the equation here. And I'm also gonna provide a default argument. Default arguments or arguments with default values always come last.
>> Nina Zakharenko: To pass in a default argument, you just give it a name, equals, and then a string or a number, kind of whatever you want here.

[00:03:38]
And I'm gonna print out the same thing I did before.
>> Nina Zakharenko: Okay, now I can call say greeting with Nina. What will this print out?
>> Student2: Hello, Nina.
>> Nina Zakharenko: That's right, why? Because hello is our default argument. I can also pass in a greeting now. Let's say Bonjour.

[00:04:18]
>> Nina Zakharenko: So unlike the required arguments where I had to have the exact right amount or I got an error, this default argument, it's optional. If I don't provide it, I will get the default value specified here. But if I do, that gets overwritten.
>> Nina Zakharenko: It's really useful, right?

[00:04:41]
I use this a ton in my code.
>> Nina Zakharenko: Just make sure that your default arguments always come last. If you don't declare them in this way, you're going to get a syntax error.
>> Nina Zakharenko: And just quickly show you what that is. Say I had a say_greeting_bad and I tried to say greeting='Hello' and then the required argument of name.

[00:05:19]
Let me give it a.
>> Nina Zakharenko: Let me give the function some content so it doesn't error out early. We'll see here syntax error, non-default argument follows default argument. And now you all know what that means, right, wrong order.
>> Nina Zakharenko: In my say_greeting function here, do I still have to provide this name argument?

[00:05:57]
>> Nina Zakharenko: What do you guys think?
>> Student3: You mean when you call it?
>> Nina Zakharenko: Yes.
>> Student3: Yes.
>> Nina Zakharenko: Okay, I do, right, because positional arguments are always required. If I try to call say_greeting with nothing, then I get my type error, missing one required positional parameter. So introducing default arguments doesn't change anything about that.

[00:06:21]
But you can also pass in none, some, or all of the keyword arguments, right? Keyword arguments are optional. So earlier today we saw a function that created a query for the GitHub API and it took a few QR tasks. Let's say the language is JavaScript. The minimum number of stars is 50 and the sort is descending.

[00:06:59]
>> Nina Zakharenko: Now we can return a f string. Let's just say the language is the language, followed by the number of stars and the sort.
>> Nina Zakharenko: What will I see printed out if I call this with no arguments?
>> Student3: You'll see the default values.
>> Nina Zakharenko: The default values, that's exactly right.

[00:07:34]
It's JavaScript 50 and descending. But I can pass in none. One, let's say I want the language to be Python. What will the sort and the number of stars be? You guys?
>> Student: 50.
>> Nina Zakharenko: Yep, I can also pass in all of these arguments.
>> Nina Zakharenko: And notice that they don't have to be in the same order, that's because they're labeled.

[00:08:09]
Right, so I'm being very explicit about what I'm passing in. You can also, let's say I had a function foo here. It took one positional argument and one default argument.
>> Nina Zakharenko: I can also use the label of the positional argument if I wanted to. So I could call foo with 3.

[00:08:41]
That just automatically sets a to 3 within this function, and b to 5. I could call foo,
>> Nina Zakharenko: By setting 3 in the right position and then passing in b as 6. In Python also if you just wanna be extra explicit about what you're doing, you can pass in the label of A, right?

[00:09:11]
So the positional argument you can pass in that label and you can pass on the label of the keyword argument, it does the same thing.