Understanding Context Manager in Python

Photo by Kevin Ku on Unsplash

Context managers are a useful feature of python. The reason why they are so useful is that they correctly respond to a pattern. There are many situations in which we want to run some code that has pre-conditions and post-conditions meaning that we want to run things before and after a main action, respectively. Context managers are great tools to use in those situations.

Most of the time we see context managers around resource management. For example, in situations when we open files, we want to make sure that they are closed after processing or if we open a connection to a service or even a socket, we want to be sure to close it accordingly. In all these cases, we want to think about to free all the resources that were allocated and a clean way to do is to use a finally block. Let’s see an example:

file_data = open(filename)
try:
    process_file(file_data)
finally:
    file_data.close()

A better and pythonic way of achieving the above task is using the with statement as shown below:

with open(filename) as file_data:
    process_file(file_data)

The with statement(PEP-343) enters the context manager. In this case, the open function implements the context manager protocol, which means that the file will be automatically closed when the block is finished, even if an exception…