Python Build a Directory Size Calculator

This Python tutorial explains Build a Directory Size Calculator. Follow the example, inspect the output, and practise an input change so you understand the behavior rather than simply copying the syntax.

What This Feature Does

Calculate the total size of files inside a directory tree.

Path.rglob() and Path.stat().st_size can sum bytes across ordinary files. Symlinks, inaccessible files, changing directory trees, and duplicate hard links need deliberate policy; this simple example counts accessible regular file entries.

When to Use It

This technique belongs to pathlib and file paths. It is useful when the input, operation and expected outcome are known. Start with a small controlled example before integrating it into a larger workflow.

Step-by-Step Python Example

Read the code once before running it. Notice which values are inputs, which function or method performs the work, and whether the result is returned or stored by changing an existing object.

from pathlib import Path
from tempfile import TemporaryDirectory

with TemporaryDirectory() as temporary_folder:
    root_folder = Path(temporary_folder)
    (root_folder / "first.bin").write_bytes(b"1234")
    nested_folder = root_folder / "subfolder"
    nested_folder.mkdir()
    (nested_folder / "second.bin").write_bytes(b"abc")
    size_bytes = sum(file_path.stat().st_size for file_path in root_folder.rglob("*") if file_path.is_file())
    print(size_bytes)

Understanding the Code

First, the imports make pathlib, tempfile available. They provide the filesystem, data or standard-library functions used later.
Find the call TemporaryDirectory(). Its parameters determine the specific operation demonstrated in the title.
Its purpose is to calculate the total size of files inside a directory tree. Compare this description against the result printed by the program.
The sample uses TemporaryDirectory() so any practice files are removed after the context ends; it does not work on your real documents.
The print() expressions display a checkable outcome. Print values and exception names are not substitutes for the program result itself.

Expected Output

The output is the observable result of the sample operation. Compare its value and type with the explanation, not just whether the program runs.

Important Details and Edge Cases

A production scanner should handle OSError and decide whether to follow symlinks.

Directory sizes may differ from allocated disk usage; hard links, sparse files and symlinks require explicit policies.

Practice: Try It Yourself

Calculate the size of a test directory and convert the result to KiB.

Begin by copying the example into a separate practice file. Change one input at a time, run it again, and describe why the result changed. If the exercise writes or deletes files, keep it inside a temporary test folder.

Official Python Documentation

For the complete reference, see the Python standard library documentation.

Common Beginner Mistakes

Counting directory metadata as regular file content without distinguishing file types.
Assuming files cannot disappear or change during a filesystem scan.
Directory sizes may differ from allocated disk usage; hard links, sparse files and symlinks require explicit policies.

Key Takeaways

Calculate the total size of files inside a directory tree.
Path.rglob() and Path.stat().st_size can sum bytes across ordinary files. Symlinks, inaccessible files, changing directory trees, and duplicate hard links need deliberate policy; this simple example counts accessible regular file entries.
Avoid this common pitfall: Counting directory metadata as regular file content without distinguishing file types.