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

python with-statement
prosseek picture prosseek · Apr 29, 2010 · Viewed 8.7k times · Source 
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")
f.close()

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

Answer

mg. picture mg. · Apr 29, 2010

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

f = open("hello.txt", "wb")
try:
    f.write("Hello Python!\n")
finally:
    f.close()

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.

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