Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 9: Real Estate Analysis App
Lecture: Concept: Python 3 AND Python 2
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Let's take a moment and look at this core concept
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of one mechanism for supporting both Python 2 and Python 3.
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You saw in our previous example that we wanted to use
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the statistics module to compute the mean,
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now I realize there are many ways to compute the mean,
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we don't need to fall back on this, it's a pretty simple mechanism
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but the idea is there is some module or some feature
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in a later version of Python that wasn't supported in a prior one.
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So this is not even about Python 2 versus Python 3,
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this is like Python 3.4 versus previous versions, ok,
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so the statistics module is imported in Python 3.4.3
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if we run this code on anything earlier than that,
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it's going to fail, it's going to say there is no module statistics, right,
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if we have it it's a super easy way to compute
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the mean of a set of numbers, you can see below,
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we've got a bunch of numbers, static.mean numbers boom,
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out comes the average.
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But it fails on a lot of the versions of Python.
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So what do we do?
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One way we can solve this problem is we can use a try and just an empty except,
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there are possible problems you can expose yourself to here,
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but in this simple case it definitely works well.
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So, we can say it look, let's try to import the statistics module,
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if it doesn't work it's going to throw an exception
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and we could actually catch the right type of exception,
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we'll get into exceptions later in the next app,
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but it's easy enough for us to go and write the statistics to stand_in.py
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and we define a mean method and it takes the same parameters
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as the real one and the implementation you saw in the previous example write it,
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it was quite easy.
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So the way we solve our problem
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and we get sort of code that runs on all the versions of Python is
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we try to import the statistics on new versions that just works
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and uses the best new module for that if it doesn't work
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it's going to fail fall into the except block and we are going to use
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this specific type of import say we are going to import statistics to stand_in
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and we are going to actually give it the name statistics
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for this particular file and since it's a mean method,
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the statistics.mean it works exactly as we would expect.
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Boom, now our code works on all the versions of Python, just like that.
