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In the last lesson, we saw how different it was when we tried to use the turtle's
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write function
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and we saw all of the arguments available listed, versus when we tried to use the
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Tkinter label's pack method,
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and notice how there's actually very few arguments that are listed.
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And yet, somehow there's all of these parameters that we can change
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when we look at the documentation, like expand or side.
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So let's set that side to equal left,
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and I'm going to delete the rest of the turtle code.
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And now you can see our label is placed on the left side of our screen.
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How is it that these parameters,
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even though they're not listed in the list of properties,
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how is it that we're able to use them just by typing them in? Well,
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to understand this, we have to learn a bit more about advanced arguments.
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Not how to argue better,
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but how to use advanced Python arguments in order to specify a wider
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range of inputs.
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We've already seen how keyword arguments work. For example,
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here I have a function and I have three keyword arguments,
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a, b, and c. And when I call the function,
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I can provide those inputs, a, b, and c in any order I want
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as long as I've got the keyword in front.
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So c = 3, a = 1, and b = 2.
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Now what if when I use this function,
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it's nine out of ten times, a is going to be equal to 1, b is 2 and c as 3.
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Why is it that when I call the function, I always have to put in these values?
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That seems a bit of a wasted effort, right?
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Python has a very neat way of solving this by creating arguments that have
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default values.
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We can do this by simply changing the function declaration.
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So when we create our function,
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we can already give it some values to start off with. So we can say that a
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should be equal to 1, b = 2 and c = 3, and these
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are the default values.
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So that means when I call this function and I want to use the default values,
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I don't actually have to provide any inputs and it will just go along as it
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would before. Now,
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if, however, I wanted to modify one of those inputs,
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let's say I wanted to give a custom value for b
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rather than let it be equal to the default value of 2, well,
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then I can just change the value of b, b = 5. And the rest,
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so a and c, will still take on their default values.
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Notice when I called tim.write,
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this write method takes five inputs; self,
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because it's a method and associated with the turtle class,
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it takes an argument which is what it is going to write,
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move, align and font. Now,
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if I wanted to use tim.turtle to just write
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some sort of text,
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I can actually just put in this. And when I run this code,
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you'll see that I've got some piece of text being written.
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But how is it that I've got all of these other inputs
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which I've just basically completely ignored? What about move?
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What about align? What about fonts? Well, as you can see,
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they have the =...,
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which is trying to tell you that they've already got a default value.
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And in fact, if I hover over this write function,
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you can see that in the quick docs that pops up,
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it tells me that the argument,
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or the arg,
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which is what it is to be written to the screen, move
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which is optional which can be set as true or false, align
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which is optional, font which is optional.
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The reason why they're optional is because all of these actually have a default
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value. For example,
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move, by default, is false; align by default is centered,
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and there's also a default font.
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So that means that all we have to do is just to provide the required arguments.
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If I don't add anything at all when I call this write method, you can see
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I do in fact get an error here.
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And it says write is missing one required positional argument,
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which is that first arg
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which is the thing that it's expecting to write. I mean,
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if you're calling turtle to do some writing and you not telling it what to write,
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that's a bit of a problem.
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So this ARG is a required argument because it doesn't have that =... at
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the end. So this you have to provide. But once you've done that,
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then the rest of them all have default values.
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They already know how to behave and what to do
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even if you don't tell them anything extra. Now, however,
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if you wanted to modify one of those arguments,
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let's say I decide to change the font to something completely different
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like Times New Roman, and make the font super large
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80 size font and change it to bold,
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then you can see that that optional setting gets implemented and it's now
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changed the font and its changed the size and also made it bold.
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But this was completely
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optional.
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And this is all down to creating the function with default values.