define-callable.md

define-callable

This transformer cares about a weird choice to drop the callable() builtin in python 3.0. It was resurrected in python 3.2. As python3 did not catch on for production-level code until python 3.3 this omission is often overlooked when writing portable code.

In any case, if a python3.0 or python3.1 is encountered then some boilerplate-code gets activated for callable() bringing back the global builtin function. As always, the extra code in the import section gets only generated when some the callable function was actually used in the given script.

    # original
    def func1(x: Any):
        if callable(x):
            repr(x())

    # transformed
    import sys
    if sys.version_info >= (3, 0) and sys.version_info < (3, 2):
    
        def callable(x):
            return hasattr(x, '__call__')
    
    def func1(x):
        if callable(x):
            repr(x())

Note that if a --python-version of 3.2 or later is selected then this transformer will not be executed at all. As it is extremely unlikely to find a python 3.0 in 3.1 on a production server, it safe to use "--no-define-callable" or just "--noc" on the commandline (or use no-define-callable = 1 in the [tool.strip-python3] section in the pyproject.toml file)