Raincoat

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Raincoat has you covered when you can’t stay DRY. When the time comes where you HAVE to copy code from a third party, Raincoat will let you know when this code is changed so that you can update your local copy.

The problem

Lets say you’re using a lib named umbrella which provides a function named use_umbrella and it reads as such :

def use_umbrella(umbrella):

    # Prepare umbrella
    umbrella.remove_pouch()
    umbrella.open()

    # Use umbrella
    while rain_detector.still_raining():
        umbrella.keep_over_me()

    # Put umbrella away
    umbrella.close()
    while not umbrella.is_wet():
        time.sleep(1)
    umbrella.put_pouch()

This function does what it says it does, but it’s not ideally splitted, depending on your needs. For example, maybe at some point you realize you need each of the 3 separate parts to be a function of its own. Or maybe you can’t call time.sleep in your app. Or do something else with the umbrella when it’s open like dance with it.

It’s also possible that you can’t really make a pull request because your needs are specific, or you don’t have the time (that’s sad but, hey, I know it happens) or any other personnal reason. So what do you do? There’s no real alternative. You copy and paste the code, modify it to fit your needs and use your modified version. And whenever there’s a change to the upstream function, chances are you’ll never know.

The solution

Enter Raincoat.

You have made your own private copy of umbrella.use_umbrella (umbrella being at the time at version 14.5.7) and it looks like this :

def dance_with_umbrella(umbrella):
        """
    I'm siiiiiinging in the rain !
    """
    # Prepare umbrella
    umbrella.remove_pouch()
    umbrella.open()

    # Use umbrella
    while rain_detector.still_raining():
        Dancer.sing_in_the_rain(umbrella)

    # Put umbrella away
    umbrella.close()
    while not umbrella.is_wet()
        time.sleep(1)
    umbrella.put_pouch()

Now simply add a comment somewhere (preferably just after the docstring) that says something like:

def dance_with_umbrella(umbrella):
    """
    I'm siiiiiinging in the rain !
    """
    # This code was adapted from the original umbrella.use_umbrella function
    # (we just changed the part inside the middle while loop)
    # Raincoat: pypi package: umbrella==14.5.7 path: umbrella/__init__.py element: use_umbrella

    ...

Now, install and run raincoat in your project:

$ pip install raincoat
    $ raincoat

It will:

  • Grep the code for all # Raincoat: comments and for each comment:

  • Look at the currently installed version of the lib (say, umbrella 16.0.3) (or, if not found, the latest version)

  • Compare with the version in the Raincoat comment (here, 14.5.7)

  • If they are different, download and pip install the specified version in a temp dir (using cached wheel as pip does by default, this should be quite fast in most cases)

  • Locate the code using the provided path for both the downloaded and the currently installed versions

  • Diff it

  • Tell you if there’s a difference (and mention the location of the original Raincoat comment)

Whether there is something to change or not, you’ve now verified your code with umbrella 16.0.3, so you can update manually the umbrella comment.

# Raincoat: pypi package: umbrella==16.0.3 path: umbrella/__init__.py element: use_umbrella"

Raincoat can be used like a linter, you can integrate it in CI, make it a tox target…

And beyond !

Actually, the base principle of Raincoat can be extended to many other subjects than PyPI packages. To fit this, Raincoat was written with a modular achitecture allowing other kinds of Raincoat comments.

For now Raincoat comes with:

  • PyPI: The module presented above

  • Django: A module that checks if a given bug in Django for which you may have had to write a workaround is fixed in your (or the latest) version of Django. Syntax is :

# Raincoat: django ticket: #26976
  • PyGitHub : Same as the PyPI module but using Github. It’s useful if your upstream is a python package that’s not on PyPI, like, say, the Python Standard Library itself. Say you want to know if the element Maildir._lookup in the file Lib/mailbox.py changed on the master branch since commit 43ba8861. What you can do is:

# Raincoat: pygithub repo: python/cpython@43ba8861 branch: master path: Lib/mailbox.py element: Maildir._lookup

You can also create your own Raincoat comment checker.

You can head to the Quickstart section for a general tour or to the How-To sections for specific features. The Discussions section should hopefully answer your questions. Otherwise, feel free to open an issue.