[temporarily replace file] Sometimes when testing I want to replace a file with a test file. This context manager does that. #testing

temp_backup.py

import contextlib
import shutil
from pathlib import Path


@contextlib.contextmanager
def replace_file(orig, replace_with):
    if not replace_with.is_file():
        raise ValueError("{} does not exist.".format(replace_with))
    if orig.is_file():

        # Move orig to backup location
        backup_to = backup_fn(orig)
        _orig = str(orig)
        orig.rename(backup_to)
        backed_up_orig = Path(backup_to)

        # Replace orig with replacement
        shutil.copy(str(replace_with), str(orig))

        yield

        # Restore original
        backed_up_orig.rename(orig)
    else:

        # No original, just just copy replacement
        shutil.copy(str(replace_with), str(orig))

        yield

        # Remove replacment since there was no original file
        orig.unlink(orig)


def backup_fn(path, backup_ext=".bak"):
    # Try just slapping the backup_ext on the file
    potential = Path(str(path) + backup_ext)
    if not potential.exists():
        return potential

    # Backup already exists so try adding an incremental interger to the fn
    for i in range(100):
        potential = Path(str(path) + backup_ext + str(i))
        if not potential.exists():
            return potential

    raise ValueError("Unable to choose a filename to back up {} to!".format(path))