{"id":1089,"date":"2023-05-05T22:39:00","date_gmt":"2023-05-05T17:09:00","guid":{"rendered":"https:\/\/geekpython.in\/?p=1089"},"modified":"2023-08-15T13:23:48","modified_gmt":"2023-08-15T07:53:48","slug":"context-managers-and-python-with-statement","status":"publish","type":"post","link":"https:\/\/geekpython.in\/context-managers-and-python-with-statement","title":{"rendered":"Context Managers And The ‘with’ Statement In Python: A Comprehensive Guide With Examples"},"content":{"rendered":"\n

In this article, we’ll look at context managers and how they can be used with Python’s “with<\/code>” statements and how to create our own custom context manager.<\/p>\n\n\n\n

<\/a>What Is Context Manager?<\/h2>\n\n\n\n

Resource management is critical in any programming language, and the use of system resources in programs is common.<\/p>\n\n\n\n

Assume we are working on a project where we need to establish a database connection or perform file operations; these operations consume resources that are limited in supply, so they must be released after use; otherwise, issues such as running out of memory or file descriptors, or exceeding the maximum number of connections or network bandwidth can arise.<\/p>\n\n\n\n

Context managers<\/strong> come to the rescue in these situations; they are used to prepare resources for use by the program and then free resources when the resources are no longer required, even if exceptions have occurred.<\/p>\n\n\n\n

<\/a>Why Use Context Manager?<\/h2>\n\n\n\n

As previously discussed, context managers provide a mechanism for the setup and teardown of the resources associated with the program. It improves the readability, conciseness, and maintainability of the code.<\/p>\n\n\n\n

Consider the following example, in which we perform a file writing operation without using the with<\/code> statement.<\/p>\n\n\n\n

# Opening file\nfile = open('sample.txt', 'w')\ntry:\n    # Writing data into file\n    data = file.write(\"Hello\")\nexcept Exception as e:\n    print(f\"Error Occurred: {e}\")\nfinally:\n    # Closing the file\n    file.close()<\/pre><\/div>\n\n\n\n
To begin, we had to write more lines of code in this approach, and we had to manually close the file in the finally<\/code> block.<\/p>\n\n\n\n
Even if an exception occurs, finally<\/code> block will ensure that the file is closed. However, using the open()<\/code> function with the with<\/code> statement reduces the excess code and eliminates the need to manually close the file.<\/p>\n\n\n\n
with open(\"sample.txt\", \"w\") as file:\n    data = file.write(\"Hello\")<\/pre><\/div>\n\n\n\n
In the preceding code, when the with<\/code> statement is executed, the open()<\/code> function’s __enter__<\/code> method is called, which returns a file object. The file object is then assigned to the variable file<\/code> by the as<\/code> clause, and the content of the sample.txt<\/code> file is written using the variable file<\/code>. Finally, when the program exits execution, the __exit__<\/code> method is invoked to close the file.<\/p>\n\n\n\n
We’ll learn more about __enter__<\/code> and __exit__<\/code> methods in the upcoming sections.<\/p>\n\n\n\n
We can check if the file is actually closed or not.<\/p>\n\n\n\n
print(file.closed)\n\n----------\nTrue<\/pre><\/div>\n\n\n\n
We received the result True<\/code>, indicating that the file is automatically closed once the execution exits the with<\/code> block.<\/p>\n\n\n\n
<\/a>Using with Statement<\/h2>\n\n\n\n
If you used the with<\/code> statement, it is likely that you also used the context manager. The with<\/code> statement is probably most commonly used when opening a file.<\/p>\n\n\n\n
# Opening a file\nwith open('sample.txt', 'r') as file:\n    content = file.read()<\/pre><\/div>\n\n\n\n
Here’s a simple program that opens a text file and reads the content. When the open()<\/code> function is evaluated after the with<\/code> statement, context manager is obtained.<\/p>\n\n\n\n
The context manager implements two methods called __enter__<\/code> and __exit__<\/code>. The __enter__<\/code> method is called at the start to prepare the resource to be used, and the __exit__<\/code> method is called at the end to release resources.<\/p>\n\n\n\n
Python runs the above code in the following order:<\/p>\n\n\n\n