Adding the document-new entry Context Managers and files

[Maet22]

Description

Adding an entry that explains the concept of context managers and introduces the ways to use concept managers with files.

Issue Solved

It was not related to an existing issue.

Type of Change

• Adding a new entry

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[Sriparno08]

Hey @Maet22, thanks for contributing to Codecademy!

I've listed all the modifications that you need to make in your entry below:

[Sriparno08]

Suggested change

	---
	Title: 'Context Managers and Files'
	Description: 'This document introduces context managers and in particular how they can be used to work with files. It details the two approaches, class-based and decorator-based, thanks to which the user can customize this experience to fit the needs of a given use case.'
	Subjects:
	- 'Computer Science'
	- 'Data Science'
	Tags:
	- 'Best Practices'
	- 'Classes'
	- 'Decorators'
	- 'Files'
	CatalogContent:
	- 'learn-python-3'
	- 'paths/computer-science'
	---
	---
	Title: 'Context Managers'
	Description: 'Context managers allow users to perform operations within a certain overarching context.'
	Subjects:
	- 'Computer Science'
	- 'Data Science'
	Tags:
	- 'Best Practices'
	- 'Classes'
	- 'Decorators'
	- 'Files'
	CatalogContent:
	- 'learn-python-3'
	- 'paths/computer-science'
	---

[Sriparno08]

Suggested change

	## Definition of a context managers
	One might want to perform some operation within a certain overarching context, be it in the form of a time counter or a database connection or the use of a [file](https://www.codecademy.com/resources/docs/python/files). This is what **context managers** allow to do by implementing a **runtime context**, within which can be perform the wanted code and that closes automatically just after, sparing to the user the hassle of doing so. Regardless of the many different use cases a context manager can be used for, the **context manager protocol** always articulates those four functionalities: open the resource, implement the runtime context, handle the possible [exceptions](https://www.codecademy.com/resources/docs/python/errors), close the resource. The user input finds its place once the runtime context is started.
	## Definition
	**Context managers** allow users to perform operations within a certain overarching context, be it in the form of a time counter or a database connection or the use of a file. They manage to do it by implementing a **runtime context**. In this context, the specified operation is first performed and then, the context automatically gets closed. This prevents the users from the hassle of closing it manually.
	Regardless of the many different use cases that context managers can be used for, the **context manager protocol** always articulates four functionalities:
	- Opening the resource
	- Implementing the runtime context
	- Handling the possible [exceptions](https://www.codecademy.com/resources/docs/python/errors)
	- Closing the resource
	Once the runtime context is started, the user input finds its place.

[Sriparno08]

Suggested change

	## Manipulate files with context managers
	The `open()` function is the standard context manager to open, perform operations on and close files.
	## File Manipulation
	The `open()` function is the standard context manager for opening, performing operations on and closing files:

[Sriparno08]

Suggested change

	# this code will print the first four lines of the poem "L'albatros"
	with open('albatros.txt','r') as poem:
	for i in range(4):
	print(poem.readline())
	# this code will however create an error as we are already outside of the indented block and therefore no longer within the context that had been setup
	print(albatros.readline())
	# Printing the first four lines of the poem "L'albatros"
	with open('albatros.txt', 'r') as poem:
	for i in range(4):
	print(poem.readline())

[Sriparno08]

Suggested change

	Output:
	The above code produces the following output:

[Sriparno08]

Suggested change

	Result:
	Here is the output:

[Sriparno08]

Suggested change

	```md
	```shell

[Sriparno08]

Suggested change

	### Decorator-based approach
	In this approach, rather than a class is defined a [generator](https://www.codecademy.com/resources/docs/python/generators) function (i.e. a function performing a _yield_ and not a _return_). This function should be _decorated_ using `@contextmanager` from the built-in module `contextlib`:
	```py
	from contextlib import contextmanager
	```
	A decorator-based context manager is also using the user input in the form of parameters provided at the instantiation. It follows the syntax _try-except-finally_, _try_ being the part where the _yield_ statement is and the core operations are done, _except_ the exceptions handling part, and _finally_ the part where the resources are closed, essentially.
	The below code shows an implementation of a decorator-based context manager thanks to which interview proposals are sent to pre-selected candidates. It is also possible (but not mandatory) to introduce some personalized elements in the indented block. If doing so this element will be placed just before the timeslot proposal.
	### Decorator-Based Approach
	In decorator-based approach, a [generator](https://www.codecademy.com/resources/docs/python/generators) function (i.e., a function performing a `_yield_ ` and not a `_return_`) is defined rather than a class. This function is _decorated_ using `@contextmanager` from the built-in module `contextlib`:
	```pseudo
	from contextlib import contextmanager
	```
	A decorator-based context manager also uses the user input in the form of parameters provided at the instantiation. It follows the syntax `_try-except-finally_`, where `_try_` being the part where the `_yield_` statement is and the core operations are done, `_except_` being the part where the exceptions are handled and `_finally_` being the part where the resources are closed.
	The below code shows an implementation of a decorator-based context manager thanks to which interview proposals are sent to pre-selected candidates. It is also possible (but not mandatory) to introduce some personalized elements in the indented block. Doing so places this element just before the timeslot proposal:

[Sriparno08]

Suggested change

	Result:
	The output for the above code is as follows:

[Sriparno08]

Suggested change

	```md
	```shell