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 3.2

Click 3.2 had to perform two changes to multi commands which were triggered by a change between Click 2 and Click 3 that had bigger consequences than anticipated.

Context Invokes

Click 3.2 contains a fix for the Context.invoke() function when used with other commands. The original intention of this function was to invoke the other command as as if it came from the command line when it was passed a context object instead of a function. This use was only documented in a single place in the documentation before and there was no proper explanation for the method in the API documentation.

The core issue is that before 3.2 this call worked against intentions:

ctx.invoke(other_command, 'arg1', 'arg2')

This was never intended to work as it does not allow Click to operate on the parameters. Given that this pattern was never documented and ill intended the decision was made to change this behavior in a bugfix release before it spreads by accident and developers depend on it.

The correct invocation for the above command is the following:

ctx.invoke(other_command, name_of_arg1='arg1', name_of_arg2='arg2')

This also allowed us to fix the issue that defaults were not handled properly by this function.

Multicommand Chaining API

Click 3 introduced multicommand chaning. This required a change in how Click internally dispatches. Unfortunately this change was not correctly implemented and it appeared that it was possible to provide an API that can inform the super command about all the subcommands that will be invoked.

This assumption however does not work with one of the API guarantees that have been given in the past. As such this functionality has been removed in 3.2 as it was already broken. Instead the accidentally broken functionality of the Context.invoked_subcommand attribute was restored.

If you do require the know which exact commands will be invoked there are different ways to cope with this. The first one is to let the subcommands all return functions and then to invoke the functions in a Context.resultcallback().

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.