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Does reading an entire file leave the file handle open?

python
resource-management
file-handling
best-practices
Alex KataevbyAlex Kataev·Feb 5, 2025
TLDR

When opening a file using the with statement, the file is automatically closed after the block:

with open('file.txt') as file: content = file.read() # Now you can safely forget about closing the file, it's done for you

If you directly open a file without the with statement, remember to manually close it:

file = open('file.txt') content = file.read() file.close() # Do not forget me, or there will be leaks!

Upon executing the statement in CPython, due to garbage collector’s reference counting, the file will get promptly closed as soon as it becomes unreachable. Even so, it is not advisable to rely on this as it can lead to potential resource leaks.

A closer look at with Statement

The with statement, brought to light in PEP 343, serves to ensure cleanup of resources whenever you're done with them.

Old-school file handling

When a file is opened devoid of with, it will remain open until explicitly closed or the program execution gets over:

file = open('file.txt', 'r') content = file.read() # File is wide open here like a 24/7 store, should be closed manually

The modern days with pathlib

If you're a fan of concise and elegant programming, then pathlib introduced in Python 3.4 might interest you:

from pathlib import Path content = Path('file.txt').read_text() # short and sweet, just like life should be

Don't worry if you're using an older version of Python, simply install pathlib2 to get similar functionality.

Secret ingredients of resource management

Serving large files

When the file happens to be huge, a wise way to use less memory is reading the file line by line:

with open('file.txt', 'r') as file: for line in file: process_line(line) # Your memory will thank you

Adding error handling

In case of pathlib.read_text(), encoding errors can be handled straightaway:

content = Path('file.txt').read_text(encoding='utf-8', errors='ignore') # Ignoring encoding errors, like ignoring toxic people in life

Sprinkle strip() to clean up

Clean data is critical when processing files. .strip() helps in removing any whitespace or newlines:

lines = [line.strip() for line in open('file.txt')] # Stripping away unwanted white spaces just like unwanted opinions

Acing resource management and longevity

Beware of the file handlers

Avoid expecting finalizers to close files. Their behavior might not be consistent upon termination of the program leading to unsettled resources.

Mind the leaks

Poor resource and file handle management can lead to resource leaks. In turn, it can affect system performance or even block operations needing those resources.

Optimizing script performance

A well-placed context manager can lead to better script performance by ensuring file handles aren't left open needlessly.

Knowing when to close up

It's vital to grasp when to close file handles:

  • After any direct file operation like .read(), .readlines(), etc., if not using 'with'.
  • When using temporary files that you manipulate programmatically.
  • Prior to deleting or altering a file’s properties; else it might cause a permission error.