Python Check If File Exists: exists, is_file and the Actual Read

Start with a small, explicit task

Create a synthetic file inside a temporary directory, compare the file and directory checks, then remove the file between checking and reading. This controlled change demonstrates why the read itself still needs appropriate error handling. No existing user path is inspected or modified.

Run the complete example

This original example was checked with Python 3.12.14. Save it as python_check_file_exists.py and run it with Python 3.12. It uses only the standard library. The assertions check the stated results.

from pathlib import Path
from tempfile import TemporaryDirectory
with TemporaryDirectory(prefix="path-check-") as folder:
    directory = Path(folder)
    path = directory / "sample.txt"
    path.write_text("sample", encoding="utf-8")
    assert directory.exists() and not directory.is_file()
    assert path.exists() and path.is_file()
    checked_before = path.exists()
    path.unlink()
    try:
        path.read_text(encoding="utf-8")
    except FileNotFoundError:
        result = "read detected missing file"
    else:
        raise AssertionError("expected missing file")
    assert checked_before and not path.exists()
    print("directory exists but is not a file")
    print("prior check:", checked_before)
    print(result)

Explain the result

The directory passes exists but fails is_file, so existence alone is not enough when the application requires file content. The synthetic text file passes both. The script then deliberately deletes it before reading, turning a previously true existence result into a stale observation.

FileNotFoundError comes from the actual attempted read and addresses the state when that operation occurs. This is the important distinction: a preliminary check can inform a message or branch, but cannot reserve the file or prove a subsequent read will succeed. Other failures, such as insufficient permission, require their own handling based on the application.

Avoid these mistakes

Do not claim that is_file verifies readable content or a particular file format. It answers a path-type question. Keep exception handling close to the operation whose failure you can meaningfully address, and avoid swallowing all filesystem errors under a misleading “missing file” message.