oldoc63
commented
1 year ago In the above script we added "Montreal" as a new line in our file fun_cities.txt. However, since we use the older-style syntax, we had to remember to close the file afterwards. Since this is necessarily more verbose (requires at least one more line of code) without being more expressive, using with is preferred.
We've been opening these files with this with block so far, but it seems a little weird that we can only use our file variable in the indented block. Why is that? The with keyword invokes something called a context manager for the file that we're calling open() on. This context manager takes care of opening the file when we call open() and then closing the file after we leave the indented block.
Why is closing the file so complicated? Well, most other aspects of our code deal with things that Python itself controls. All the variables you create: integers, lists, dictionaries - these are all Python objects, and Python knows how to clean them up when it's done with them. Since your files exist outside your Python script, we need to tell Python when we are done with them so that it can close the connection to that file. Leaving a file connection open unnecessarily can affect performance or impact other programs on your computer that might be trying to access that file.
The with syntax replaces older ways to access files where you need to call .close() on the file object manually. We can still open up a file and append to it with the old syntax, as long a we remember to close the file connection afterwards.