CODEWITHSUNDEEP
pythonpython-2.7
mfcabrera
mfcabrera

Reputation: 781

Python opening and close file - not intuitive

Is it me or to open or close a file in python uses different methods making it really not intuitive? Is there a better way to do it?

example:

f = open('file.txt', 'r')
try:
# do stuff with f
finally:
   f.close()

Now, why I use the built-in "function" open but to close the file I don't have function "close" but I have to call the "object" method "close".

Upvotes: 1

Views: 221

Answers (2)

thegrinner
thegrinner

Reputation: 12243

Use the with keyword to make it a bit more intuitive. It will automatically close the file when you dedent. From the docs:

The ‘with‘ statement clarifies code that previously would use try...finally blocks to ensure that clean-up code is executed.

...

After this statement has executed, the file object in f will have been automatically closed, even if the for loop raised an exception part- way through the block.

An example:

with open('file.txt', 'r') as f:
    # do stuff with f

# Do some other stuff - we dropped down a level of indentation, so the file is closed

More specifically, it will initially call the context's __enter__ method - this does the initial file opening. Whatever is returned by __enter__ is set using the as statement - in this case, the file returns self and it will be set to f. When the with block is done, it will call the context's __exit__ method. For a file context, this does the normal finally block handling of closing the file.

Note that the with block won't handle exceptions for you, it just ensures __exit__ is called (and that will gracefully closed the file) even if they do happen . So if you have a ValueError while working with the file you'll still need a try...catch block inside the with block to handle whatever that may do to your calculations/script/etc.

As Marcin noted, most languages do this in a try...catch...finally block. Java, for example, does this:

BufferedReader reader = null;
try {
    reader = new BufferedReader(new File("file.txt"));
    // Read in data and do stuff
} catch (Exception e) {
    // Shouldn't be this generic, but you get the idea
    e.printStackTrace();
} finally {
    // Always executes
    if (reader != null) reader.close();
}

Upvotes: 6

t-8ch
t-8ch

Reputation: 2713

This does the same:

with open('file.txt', 'r') as f:
    # do stuff

Upvotes: 2

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