What’s the advantage of using ‘with .. as’ statement in Python?

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Question :

What’s the advantage of using ‘with .. as’ statement in Python?
with open("hello.txt", "wb") as f:
    f.write("Hello Python!n")

seems to be the same as

f = open("hello.txt", "wb")
f.write("Hello Python!n")

What’s the advantage of using open .. as instead of f = ?
Is it just syntactic sugar? Just saving one line of code?

Asked By: prosseek


Answer #1:

In order to be equivalent to the with statement version, the code you wrote should look instead like this:

f = open("hello.txt", "wb")
    f.write("Hello Python!n")

While this might seem like syntactic sugar, it ensures that you release resources. Generally the world is more complex than these contrived examples and if you forget a try.. except... or fail to handle an extreme case, you have resource leaks on your hands.

The with statement saves you from those leaks, making it easier to write clean code. For a complete explanation, look at PEP 343, it has plenty of examples.

Answered By: prosseek

Answer #2:

If f.write throws an exception, f.close() is called when you use with and not called in the second case. Also f has a smaller scope and the code is cleaner when using with.

Answered By: mg.

Answer #3:

The former still closes f if an exception occurs during the f.write().

Answered By: Kathy Van Stone

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