jayd2446 / safer

✏️ safer: a safer file writer ✏️

✏️safer: a safer file writer ✏️

No more partial writes or corruption! safer writes a whole file or nothing.

safer.writer() and safer.printer() are context managers that open a file for writing or printing: if an Exception is raised, then the original file is left unaltered.

Install safer from the command line using pip:

pip install safer

Tested on Python 2.7, and 3.4 through 3.8.

EXAMPLES

safer.writer

# dangerous
with open(file, 'w') as fp:
    json.dump(data, fp)    # If this fails, the file is corrupted

# safer
with safer.writer(file) as fp:
    json.dump(data, fp)    # If this fails, the file is unaltered

safer.printer

# dangerous
with open(file, 'w') as fp:
    for item in items:
        print(item, file=fp)
    # Prints a partial file if ``items`` raises an exception while iterating
    # or any ``item.__str__()`` raises an exception

# safer
with safer.printer(file) as print:
    for item in items:
        print(item)
    # Either the whole file is written, or nothing

API call documentation

safer.writer(file, mode='w', create_parent=False, delete_failures=True, **kwargs)

A context manager that yields a writable stream returned from open(), but leaves the file unchanged if an exception is raised.

It uses an extra temporary file which is renamed over the file only after the context manager exits successfully: this requires as much disk space as the old and new files put together.

If mode contains either 'a' (append), or '+' (update), then the original file will be copied to the temporary file before writing starts.

Arguments:

file:

Path to the file to be opened

mode:

Mode string passed to open()

create_parent:

If true, create the parent directory of the file if it doesn't exist

delete_failures:

If true, the temporary file is deleted if there is an exception

kwargs:

Keywords passed to open()

safer.printer(file, mode='w', create_parent=False, delete_failures=True, **kwargs)

A context manager that yields a function that prints to the opened file, but leaves the file unchanged if an exception is raised.

It uses an extra temporary file which is renamed over the file only after the context manager exits successfully: this requires as much disk space as the old and new files put together.

If mode contains either 'a' (append), or '+' (update), then the original file will be copied to the temporary file before writing starts.

Arguments:

file:

Path to the file to be opened

mode:

Mode string passed to open()

create_parent:

If true, create the parent directory of the file if it doesn't exist

delete_failures:

If true, the temporary file is deleted if there is an exception

kwargs:

Keywords passed to open()