Python for .NET Developers Transcripts
Chapter: OOP: Object-Oriented Python
Lecture: Iterating the spots
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There were two reasons I added this idea of the parking lot. The first one was I wanted to talk about the staticmethods and how we can do this
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to create a factory type of thing. Here's the second. So, what I want to do is instead of just printing this out and go
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Oh, this is a super way to look at it. I'm sure my users would love to just have a flat dictionary dumped here with no data in it.
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There's a couple of improvements. First of all notice this is not an incredible representation of the SportsCar or the BasicCar. Whatever, right?
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It would be nice to have something better. So, I can go to the car and I can implement one of the what are called, magic methods
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or Python data model methods. And those are the dunder methods. So, if I go over here and type def and double underscore
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I have abs for absolute value, add async Enter what ending what something means what boolean conversion, deep copy copy
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Notice there are a ton of these things here. In .NET, you might override what ToString mean here. So we can do the same, like this.
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But it actually turns out there's two that get called in different situations. You can, if you use it in a string
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this get called if you just dump it out like we just did than this one gets called. We can actually just return one when the other exists.
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So let's just return a string that has the type name here. And then, maybe it says like the model name and the price.
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And if want to have digit grouping not too many zeros, things like that say put a little format, :x.0f,0f I think it is :,0f
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There is a comma, There is a .0f and over here, we are going to say type(self).__name__. I think that'll do it. Let's run it again.
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Check this out. Sports car. Model. Corvette. That's the price. Basic Car. Wind Star. Price, notice the digit grouping and there is no extra zeros
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even though it's a float. Pretty cool right? So this these two methods represent part of Python's special data model their dunder methods.
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This is how you implement some of the core interfaces of Python. So for example, what I would like to do up here instead would say something like this
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for spot, car in lot: something like that. I'd like to print out a statement about it. Like this. And I would also say if car, like so
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we got to make sure there is a car here and then we are going to print it out. We don't want to print the empty ones. I noticed, PyCharm says mmm
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We thought there would be a collections.interval here but this is just a random parking lot. It's not going to go so well if you try this.
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Let's see. Nope. It didn't go so well. Nope, not interval. This should be like C# compilation error object lot is not IEnumberable<T>
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or something like this right? So, how do we fix this? Well, we go back and we use one of these dunder methods.
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These magic methods. Like the constructor is. So we go over here. I'll put it below. And here is called __iter__. We implement __iter__.
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And what we have to do is return something that is the collections we are trying to loop over. Let's just say i, yield i. Here we go
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Created a generator that shoots out the items. So here we go. Here is the spot. It is A1 and it has the car, sports car
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which has this represents this, this two string equivalent, the __str__, implementation over here. Pretty cool huh?
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This lets us dig into the classes and change the way they basically intergrate the Python language. Right? We implemented __iter__
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over here to allow us to loop over the lot. And then we implemented __repr__ and __str__. This one would be the str.
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But if we printed, we just did print car like that would be the __repr__ version we implemented that here to change basically
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the two string representation for that object.