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A long time ago, we've talked about Python data types.
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So the data types that we've been working with include things like integers,
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strings, floating point numbers and booleans.
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And we've seen how you can interchange between different data types by casting.
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And we've also seen that in Python, the data types are flexible.
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So you could create a variable and then change its data type later on.
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This is known as dynamic typing.
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Now I want to show you another thing that you can do with data types to make
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your code less error prone.
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Let's say that we were to create a variable, for example, a variable called age.
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Now, normally we would set it with an equal sign.
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But you can also simply declare its data type and then leave it as is.
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So this means that later on, at some point,
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once you've actually gotten the age of from the user or you've worked it out,
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then at that point, you can set it. And this age now has to match
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the data type over here. So for example,
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if I was to change this to 12 using a string, then you can see that my
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PyCharm,
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my IDE, is now being very helpful in telling me that this age thing ages ago
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when you created it, you said it should be an integer. Instead, I got a string.
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So this is quite helpful. You can do this with all of the basic data types.
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So for example, age is an int, name is a string,
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height is a float and is_human is a boolean.
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Now we can also specify the data type inside a function.
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So for example,
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if I was to create a function here called a police_check and it took the age as
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an input, and then inside the police_check function, I would check well,
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if the age is over 18,
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then maybe we would have some sort of variable called can_drive and we could set
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that to true.
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But otherwise, we can set that to false
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right?
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Now, we're going to return this as the output.
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So now at some point we can call our police_check function,
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pass in the age and if we print this out,
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you can see that it's going to give me false for age 12.
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And if I decide to say I'm 19, well, then we get true.
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We can actually use the output from this function to create a print statement,
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for example.
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So if the police check passes, then the policeman tells you, you may pass.
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Otherwise you might have to pay a fine or spend a night in jail.
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So this is our function
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and if we were to use this function
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police_check at some point
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way down the line where we've forgotten what we created for this function
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and we can't look it up very easily without scrolling up hundreds of lines of
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code, now, if at this point we've mistaken the input type
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and we put in, for example, 12 as a string,
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then this is actually going to give us a type error and it throws an exception
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crashing our
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app. One of the ways that we can make our lives a little bit easier is by
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declaring a type for this input. So we do it in the same way as you see above.
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We can add a colon and then we can specify the data type of this particular
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input. So now when we actually write this line of code,
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you can see immediately we get this part highlighted.
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And if I hover over it, it tells me that this input expected a datatype
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that's an integer and instead I gave it a string.
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So this is a quick hint for us to fix our code before we even run it and get
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into trouble and create
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bugs. In addition,
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you can also specify the data type of the output of a function,
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and you do that by creating a little arrow with a hyphen and an angle bracket.
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So now we can say that this particular function is expected to return a boolean
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data type.
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And my return statement does in fact comply with this because can_drive can only
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be true or false. Now, if I forget that this is what I need
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and at some point I return let's say a string,
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then also I'm getting this warning highlight here.
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And when I hover over it again, it's expecting a boolean
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but instead I'm giving it a string.
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This is known as a type hint in Python.
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And it is a feature that we got relatively recently from Python
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and it has a lot of benefits especially when you want your IDE, for example
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PyCharm,
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to help you spot potential bugs and keep your code safer and spend less time
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debugging and more time writing code.
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So we've seen how we can declare a data type for a variable like this
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and we've also seen how we can declare data type for the return type like this.
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That's all there is to it.