#100DaysOfCode in Python Transcripts
Chapter: Days 34-36: Refactoring / Pythonic code
Lecture: Refactoring 3: with statement (context managers)
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Right, next up is the with statement.
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You all have worked with files by now, I suppose.
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The way to open and close files is like this.
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That's fine, that's not optimal
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but if an exception occurs between the open
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and close statements.
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Let's demo that here.
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So we write hello and for some reason an exception happens.
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The problem here is that the file
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handle called f stayed open.
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So if I check now for is f closed?
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False, it's still open.
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So it's leaking resources into your program
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which is a problem, right?
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One way to avoid this is to use try
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and use except finally block.
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Try an operation, you catch the exception, if there's one
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and the finally block always execute,
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so you could put f.close in
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there to make sure it always closes, right?
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You would write something like this.
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Let's just trigger an exception.
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I divide by zero which is going to
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give me a ZeroDivision error.
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Let's catch that here.
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Finally, I will always close my file handle
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and I do that here.
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Open the file, write something,
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trigger ZeroDivision error, catch it
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and either working or failing, I always get f.close.
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Let's see if the file handle now is closed.
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And indeed it is closed.
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That's cool, right?
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This is much better code, but there's even
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a better, more pathonic way to do the above
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and it's to use a context manager or the with statement.
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I can rewrite the previous code as with open
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This is the same code and the nice thing
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about with is once you go out of the block
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it auto-closes your resource.
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In this case the file handle f.
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This raises the exception as we told it to do.
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Let's see if f is closed.
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And True.
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Look at that.
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I mean although I like try except finally,
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it's definitely a good feature.
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This is just shorter, more pathonic way to do it.
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Use with statements or context manager if
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you have to deal with resources that
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have some sort of closure at the end.
