Python with

The with keyword in Python is used to wrap the execution of a block of code within methods defined by a context manager. It simplifies resource management — automatically handling setup and teardown operations like opening and closing files, acquiring and releasing locks, or connecting and disconnecting from databases.

When a block under with is executed:

1. The context manager’s __enter__() method is called.
2. The block of code inside the with statement runs.
3. The context manager’s __exit__() method is automatically called after the block finishes — even if an error occurs.

Syntax

with expression [as variable]:
  # Code block

Parameters:

• expression: A context manager that defines __enter__() and __exit__() methods.
• variable (optional): The object returned by the __enter__() method, which can be used inside the code block.

Return value:

Returns the object provided by the context manager’s __enter__() method, if assigned using as.

Example 1: Managing File Resources

In this example, a file is opened, written to, and automatically closed after the block finishes:

with open("example.txt", "w") as file:
  file.write("Hello, World!")

Copy to clipboard
Copy to clipboard

The output of this code is:

# (No visible output)
# The file 'example.txt' is written and automatically closed.

Copy to clipboard
Copy to clipboard

Here the file is automatically opened and closed using with. Even if an error occurs while writing, file.close() is called automatically.

Example 2: Using Multiple Context Managers

In this example, two files are managed simultaneously, ensuring both are safely opened and closed:

with open("input.txt", "r") as infile, open("output.txt", "w") as outfile:
  data = infile.read()
  outfile.write(data)

Copy to clipboard
Copy to clipboard

In this example, both files are safely managed, opened at the start, and closed automatically when the block ends.

Example 3: File Handling with with

In this example, data is written to a file and then read back using separate with blocks for writing and reading:

# Writing to a file using 'with'
with open("demo.txt", "w") as file:
  file.write("Learning Python 'with' keyword!")

# Reading the same file
with open("demo.txt", "r") as file:
  content = file.read()
print(content)

Copy to clipboard
Copy to clipboard

The expected output is:

Learning Python 'with' keyword!

Copy to clipboard
Copy to clipboard