Strif is a tiny (<1000 loc) library of string and file utilities for Python 3.6+.

It’s an assembly of some functions and tricks that have repeatedly shown value in various projects. The goal is to complement the standard libs, not replace or wrap them.

Because it saves time, fills in gaps, avoids clumsy repetition, and has zero dependencies.

I’ve used many of these functions in production situations for years. But it’s not a comprehensively tested library.

It’s generally good practice when creating files to write to a file with a temporary name, and move it to a final location once the file is complete. This way, you never leave partial, incorrect versions of files in a directory due to interruptions or failures.

For example, these can (and in most cases should) be used in place of shutil.copyfile or shutil.copytree:

copyfile_atomic(source_path, dest_path, make_parents=True, backup_suffix=None)
copytree_atomic(source_path, dest_path, make_parents=True, backup_suffix=None, symlinks=False)

You also have convenience options for creating parent directories of the target, if they don’t exist. And you can keep a backup of the target, rather than clobber it, if you prefer. Used judiciously, these options can save you some boilerplate coding.

Similarly, you have syntax sugar for creating files or directories atomically using with:

with atomic_output_file("some-dir/my-final-output.txt") as temp_target:
  with open(temp_target, "w") as f:
    f.write("some contents")

Now if there is some issue during write, the output will instead be at a temporary location in the same directory. (It will have a name like some-dir/my-final-output.txt.partial.XXXXX.) This ensures integrity of the file appearing in the final location.

There are also some handy additional options:

with atomic_output_file("some-dir/my-final-output.txt",
                        make_parents=True, backup_suffix=".old.{timestamp}") as temp_target:
  with open(temp_target, "w") as f:
    f.write("some contents")

This creates parent folders as needed (a major convenience). And if you would have clobbered a previous output, it keeps a backup with a (fixed or uniquely timestamped) suffix.

Syntax sugar for auto-deleting temporary files or directories using with:

with temp_output_file("my-scratch.") as (fd, path):
  # Do a bunch of stuff with the opened file descriptor or path, knowing
  # it will be removed assuming successful termination.


with temp_output_dir("work-dir.", dir="/var/tmp") as work_dir:
  # Create some files in the now-existing path work_dir, and it will be
  # deleted afterwords.

Note these don’t delete files in case of error, which is usually what you want. Add always_clean=True if you want the temporary file or directory to be removed no matter what.

• Secure random base 36 identifiers: Digression: Use base 36 in general for random id strings. It is briefer than hex, avoids ugly non-alphanumeric characters like base 64, and is case insensitive, which is generally wise (e.g. due to MacOS case-insensitive filesystems).
• Secure random timestamped identifiers. These are similar, but start with an ISO timestamp plus a base 36 identifier, so that they sort chronologically but are still unique.
• Abbreviations for strings and lists: Abbreviate strings and lists in a pretty way, truncating items and adding ellipses.

Notes on atomic file operations and backups, offered by several functions:

All atomic operations with "atomic" in the sense that they do a single move of a complete file or directory into its final location. An incomplete file or directory will never appear in its final location, and multiple simultaneous operations will never yield corrupt output in the final location.

With backup_suffix, the target file or directory will be moved to an alternate location before any file or directory is put in its place. You can keep just one backup, or infinitely many by putting the special string '{timestamp}' into the backup_suffix parameter.

Note however that with directories, or with backup_suffix, both the old and the new file or directory may be absent very briefly since the old copy needs to be moved before the new one is moved into place. With files and no_backup suffix, the target is clobbered on the filesystem directly so will always exist.

pip install strif

Or add as a dependency in your setup.py.

pydoc strif

Please file issues or PRs!

Apache 2.