Upgrading To Newer Releases

Click attempts the highest level of backwards compatibility but sometimes this is not entirely possible. In case we need to break backwards compatibility this document gives you information about how to upgrade or handle backwards compatibility properly.

Upgrading to 2.0

Click 2.0 has one breaking change which is the signature for parameter callbacks. Before 2.0, the callback was invoked with (ctx, value) whereas now it’s (ctx, param, value). This change was necessary as it otherwise made reusing callbacks too complicated.

To ease the transition click will still accept old callbacks. Starting with click 3.0 it will start to issue a warning to stderr to encourage you to upgrade.

In case you want to support both click 1.0 and click 2.0, you can make a simple decorator that adjusts the signatures:

import click
from functools import update_wrapper

def compatcallback(f):
    # Click 1.0 does not have a version string stored, so we need to
    # use getattr here to be safe.
    if getattr(click, '__version__', '0.0') >= '2.0':
        return f
    return update_wrapper(lambda ctx, value: f(ctx, None, value), f)

With that helper you can then write something like this:

def callback(ctx, param, value):
    return value.upper()

Note that because click 1.0 did not pass a parameter, the param argument here would be None, so a compatibility callback could not use that argument.