Python provides a variety of features and options to improve our existing code. One such feature is the
This tutorial will demonstrate the function of the
with statement and its applications in Python.
with Statement in Python
This statement is essentially used to help handle exceptions and clear up resources as they are used. It ensures that the code is executed properly and the resources are cleaned up afterward.
Mostly, you will find the use of the
with statement in file handling. Let us discuss an example.
f = open('path\file.txt', 'w') f.write('Sample Content') f.close()
In the above example, we have opened a file using the
open() function and wrote some content using the
write() method. Then, the
close() function closed the file object and cleared up the resources.
Let’s see how the above code looks with the
with open('path\file.txt') as f: f.write('Sample Content')
In the code, we can see that, using the
with statement, we were able to eliminate the use of the
Another instance where the
with statement can be helpful is in encapsulating the
f = open('path\file.txt', 'w') try: f.write('Sample Content') finally: f.close()
try block takes a code like opening a file, and the code in the
finally block is executed regardless if the code in the
try block raises an exception. In the above example, the code in the
finally block will execute and run the
close() function, even if the
write() function raises an exception.
We have seen how we can achieve this using the
with statement in the earlier example.
We can also use the
with statement with user-defined objects, and such objects are known as context managers. They have an
__exit__ method defined.
__enter__ method executes while creating an object of this class using the
with statement. The
__exit__ method executes when the code in the
with block finishes.
class writer_class(object): def __init__(self, filename): self.filename = filename def __enter__(self): self.f = open(self.filename, "w") return self.f def __exit__(self, exception, value): self.f.close() with writer_class('file.txt') as f: f.write('DelftStack')
The objects of the above class in Python execute the
__enter__ method when created, which is used to open the file. The
close() function is put inside the
__exit__ method to close the file object when the code has been executed.
Like classes, we can use the
contextlib library to create context manager methods. These methods can be made using the
@contextmanager decorator, which is put before the defined function.
from contextlib import contextmanager @contextmanager def new_open(file): try: f = open(file, "w") yield f finally: f.close() with new_open("sample.txt") as f: f.write("DelftStack")
In the example code, we can see the use of the
@contextmanager decorator that allows us to create such methods. In the defined function, we put the complete code for creating the file object and closing the created object using the
To conclude, we discussed the
with statement in Python and its uses. We first discussed the basics of this statement and how it improves code readability and efficiency by cleaning up the resources.
We focused on its most common application with file handling to demonstrate its use. We also discussed context manager and its methods and how we can use the
with statement with them.
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