Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 10: Movie Search App
Lecture: Catching errors with try except
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We have our network working again, we searched for cats and dogs,
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we should get things about cats and dogs, but if we turn off it's going to crash.
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Not so great.
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Another thing maybe we want to do is we might want to check
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if I just enter nothing instead of actually trying to go and search for nothing
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that I don't even know what that means
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maybe we also want to validate this input and return that as an error as well.
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remember, in normal methods,
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you theoretically could return like false or none or something like that to say no,
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but in these initializers, you can't,
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there is no way to communicate an error other than an exception,
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that said, for both methods and initializers,
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often exceptions are the preferred way to do things in Python.
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So let's come down here and well do a little test
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and we can say something like this,
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if not search text or not search text.strip(),
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we need this first test here because if search text comes in as none,
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this will actually give us an exception trying to call it strip on none, ok.
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So either it's empty or it's not entirely empty but it's white space,
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then we want to basically cause some kind of error,
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we want to report an error back
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and we can say raise ValueError, it's one possible option here,
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we can say so let's try this, if I go down here and I hit cats,
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I should get NetworkError, if I come down here
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and I hit empty ValueError you must specify a search string,
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ok, so we are no longer going to be sort of sending off meaningless searches
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and in fact we can't create a movie client in a malformed state,
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we'll never be able to even allocate and initialize an object
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instead we'll raise this ValueError, ok.
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Now, in both cases, it didn't really matter what we do, our app is crashing,
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we'd like to just go no that didn't work, keep going,
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so the way we do that in Python is we come down here
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and we use what's called a try block so we say try:,
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and here is all the code we would like to interact with
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and if anywhere along the way,
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if this allocation this initialization threw us an exception
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because of here or the perform search those an exception
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because the network is down or something like this,
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regardless of where the error happens,
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we'd like to immediately start running there
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and go deal with the error so we can say except:, and for now,
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we'll just say print('YIKES, THAT SUCKED'), ok,
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so if we try this, notice there is a little warning here
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but this should help let's go hit enter, yikes, that didn't work,
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search for something else, oh, that didn't work, turn the network,
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if I come down here search for cats now, hey, it worked,
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so it's no longer crashing, that's really good
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but you'll see that PyCharm is warning us about this
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and we should improve it, it says, you are doing too broad of a catch,
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you are just catching everything
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and there is no meaningful information here giving back about it,
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let's do that next.
