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One of the most common ways to manage resources in Python is to make sure the files we use in our scripts are properly closed after use.

We already explored this concept when we used the with statement when operating on files. The with statement is the most common and pythonic way of invoking context managers in python. This means we have been using the concept of context managers all along!

Let’s recap how to use a with statement:

with open("file_name.txt", "w") as file: file.write("How you gonna win when you ain't right within?")

Here is what is happening in our small script:

  1. The with statement calls the built-in open() function on "file_name.txt" with a mode of "w" which represents write mode.
  2. The as clause assigns the object opened (the file) to a target variable called file to using inside of the context manager.
  3. file.write() writes a sentence to "file_name.txt"

But, what exactly does this have to do with resource management? In order to answer this question, we need to take a peek behind the curtain and examine what our code looks like without a with statement. Here is what the same code would look like without the use of a context manager like with:

file = open("file_name.txt", "w") try: file.write("How you gonna win when you ain't right within?") finally: file.close()

The alternative to using with would require us to manually open (using open()) and close (using close()) the file we are working on. By using the with statement in the first example, it serves as a context manager where files are automatically closed after script completion and we don’t ever have to worry about the possibility of forgetting to close a resource. Remember, leaving our resources open will hog up our finite computer resources. We are never guaranteed that Python will close the file for us if we happen to forget to do it!

In the next exercise, we’ll dive deeper into how context managers like the with statement are built. For now, let’s start using it and seeing its power compared to the alternative try/finally clauses.

Instructions

1.

Take a look at the code in the text editor. Notice that the file ('file_name.txt') was opened but never closed. This is bad practice and could lead to errors down the road.

Update this script by:

  • Putting the code that opens the file inside a try block
  • Closing open_file in a finally block using .close()
2.

Now rewrite this script in with statement form using open_file as the target variable. Use the "r" mode for read permissions.

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