How to Compare Two Files by Content Hash Equality in Python

Compares two files by hashing their contents with SHA-256, skipping the hash if file sizes differ, and returns whether they are identical.

Medium Python 3.9+ Aug 9, 2026 Files & data 14 views 0 copies

hashlib sha256 file-hashing pathlib file-comparison

Python code

22 lines

Python 3.9+

import hashlib
from pathlib import Path

def file_hash(path: Path, chunk_size: int = 8192) -> str:
    sha256 = hashlib.sha256()
    with path.open("rb") as f:
        for chunk in iter(lambda: f.read(chunk_size), b""):
            sha256.update(chunk)
    return sha256.hexdigest()

def files_are_identical(file_a: Path, file_b: Path) -> bool:
    if not file_a.exists() or not file_b.exists():
        return False
    if file_a.stat().st_size != file_b.stat().st_size:
        return False
    return file_hash(file_a) == file_hash(file_b)

if __name__ == "__main__":
    a = Path("file1.txt")
    b = Path("file2.txt")
    identical = files_are_identical(a, b)
    print(f"Files identical: {identical}")

Output

stdout

Files identical: True

How it works

The file_hash function reads files in fixed-size chunks using iter(lambda: f.read(chunk_size), b"") to avoid loading large files into memory, updating a SHA-256 digest incrementally. files_are_identical first checks both files exist and have equal sizes — a cheap early exit that prevents needless hashing when sizes differ. The final comparison hashes both files and compares the hex digests, which is fast and memory-efficient even for large files. This approach works because SHA-256 has an extremely low collision probability, making it a reliable content equality check.

Common mistakes

Forgetting to open files in binary mode ('rb'), causing encoding errors
Reading entire files with .read() instead of chunking, which consumes huge memory
Skipping the size check and hashing files even when sizes differ, wasting resources
Not verifying file existence first, leading to confusing FileNotFoundError traces

Variations

Use `hashlib.md5()` for faster hashing when files are small and collision risk is acceptable
Use `filecmp.cmp(file_a, file_b, shallow=False)` for a simple stdlib alternative without explicit hashing

Real-world use cases

Verifying that a downloaded file matches a checksum provided by the server to detect corruption.
Detecting duplicate files across storage directories without relying on filename comparisons.
Confirming a config or asset file was not altered during a deploy or sync job.

How to Compare Two Files by Content Hash Equality in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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How it works

Common mistakes

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Real-world use cases

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