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Python 3, an Illustrated Tour Transcripts

Chapter: Functions

Lecture: Walk-through: Keyword-only Arguments

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0:00
In this video, we're going to look at keyword test.

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Let's open that up, open it in your editor.

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Let's read the first assignment,

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it says one formula for force is mass times acceleration

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create a function force that takes to keyword only arguments mass and acceleration

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and returns the product of the arguments,

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put this function in the module called py3code.

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Let's open up py3code here,

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and it says at the bottom put keyword tests here

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I can split this if I want to and view both of these.

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I want to make a function called force that takes mass and acceleration here

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so def force and it takes mass and acceleration

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and returns mass times acceleration.

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Okay, I will save this now and run this guy and see if it works.

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Okay, and so it looks like I got an error here on this line here,

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when I call force 10, 9.8 it did not raise a type error and it wants to raise a type error.

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The reason why that is is because I didn't actually make a keyword only function

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I just made a normal function that takes mass and acceleration.

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So this will work and it won't raise a type error.

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The intention of the keyword only arguments is

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that it makes clear what our numbers are

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in this case it's not clear necessarily which one is mass and which one is acceleration.

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So in order to change that what we need to do is we need to put a star right in front of that.

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And now when we call this force function,

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we need to specify the mass and acceleration.

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Let's run it and make sure that it works.

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Okay, and now I'm on the other problem here

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so that part appeared to work.

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Let's go on to the next problem,

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the quadratic formula solves an equation of the form ax^2+ bx + c = 0

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write a function quad that returns a tuple with the solutions

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make a, b and c keyword only arguments,

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put this function in a module called py3code.py

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Okay, so if you remember the quadratic formula,

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it looks something like this, negative b plus or minus the square root

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of b squared minus 4ac and then all of this over 2a

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so there's my attempt at writing this out in some little language here.

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Let's see if we can implement this as a Python function here

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and with keyword only arguments

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so quad, and I'm going to put a star at the front

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because I want everyone to specify a, b and c when they call this.

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And because this can return 2 results,

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it can return the positive of the square root and the negative of the square root,

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we're going to make 2 results and return that as a tuple of both of those.

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So what I'm going to do is I'm just going to say,

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the square root part I'm going to say sqrt is equal to

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let's say b squared minus 4 times a, times c to the .5

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and then x1 is going to be equal to in parenthesis negative b plus

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the square root portion and this divided by 2 times a

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and the other solution will be this negative b minus the square root of that

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and let's return x1 and x2.

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Let's run our test over here and make sure that it works.

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Okay, and we got that it did indeed work.

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So we can see the calling here rather than saying quad 1, 3, 1 here.

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we have to explicitly say a is equal to 1, b is equal to 3 and c is equal to 1.

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Note that we can change the order of those if we want to as well.

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This just allows us to again be more explicit and not have magic numbers floating around

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but to have some context around them.