How to use the icontract._checkers.find_checker function in icontract

assert inspect.isfunction(value) or isinstance(value, (staticmethod, classmethod))

    # Determine the function to be decorated
    if inspect.isfunction(value):
        func = value
    elif isinstance(value, (staticmethod, classmethod)):
        func = value.__func__
    else:
        raise NotImplementedError("Unexpected value for a function: {}".format(value))

    # Collect preconditions and postconditions of the function
    preconditions = []  # type: List[List[Contract]]
    snapshots = []  # type: List[Snapshot]
    postconditions = []  # type: List[Contract]

    contract_checker = icontract._checkers.find_checker(func=func)
    if contract_checker is not None:
        preconditions = contract_checker.__preconditions__
        snapshots = contract_checker.__postcondition_snapshots__
        postconditions = contract_checker.__postconditions__

    # Collect the preconditions and postconditions from bases.
    #
    # Preconditions and postconditions of __init__ of base classes are deliberately ignored (and not collapsed) since
    # initialization is an operation specific to the concrete class and does not relate to the class hierarchy.
    if key not in ['__init__']:
        base_preconditions = []  # type: List[List[Contract]]
        base_snapshots = []  # type: List[Snapshot]
        base_postconditions = []  # type: List[Contract]

        bases_have_func = False
        for base in bases:

# Check if there is a checker function in the base class
                base_contract_checker = icontract._checkers.find_checker(func=base_func)

                # Ignore functions which don't have preconditions or postconditions
                if base_contract_checker is not None:
                    base_preconditions.extend(base_contract_checker.__preconditions__)
                    base_snapshots.extend(base_contract_checker.__postcondition_snapshots__)
                    base_postconditions.extend(base_contract_checker.__postconditions__)

        # Add preconditions and postconditions of the function
        preconditions = []  # type: List[List[Contract]]
        snapshots = []  # type: List[Snapshot]
        postconditions = []  # type: List[Contract]

        contract_checker = icontract._checkers.find_checker(func=func)
        if contract_checker is not None:
            preconditions = contract_checker.__preconditions__
            snapshots = contract_checker.__postcondition_snapshots__
            postconditions = contract_checker.__postconditions__

        preconditions = _collapse_preconditions(
            base_preconditions=base_preconditions,
            bases_have_func=bases_have_func,
            preconditions=preconditions,
            func=func)

        snapshots = _collapse_snapshots(base_snapshots=base_snapshots, snapshots=snapshots)

        postconditions = _collapse_postconditions(
            base_postconditions=base_postconditions, postconditions=postconditions)

if func == value.fget:
                    base_func = getattr(base, key).fget
                elif func == value.fset:
                    base_func = getattr(base, key).fset
                elif func == value.fdel:
                    base_func = getattr(base, key).fdel
                else:
                    raise NotImplementedError("Unhandled case: func neither value.fget, value.fset nor value.fdel")

                if base_func is None:
                    continue

                bases_have_func = True

                # Check if there is a checker function in the base class
                base_contract_checker = icontract._checkers.find_checker(func=base_func)

                # Ignore functions which don't have preconditions or postconditions
                if base_contract_checker is not None:
                    base_preconditions.extend(base_contract_checker.__preconditions__)
                    base_snapshots.extend(base_contract_checker.__postcondition_snapshots__)
                    base_postconditions.extend(base_contract_checker.__postconditions__)

        # Add preconditions and postconditions of the function
        preconditions = []  # type: List[List[Contract]]
        snapshots = []  # type: List[Snapshot]
        postconditions = []  # type: List[Contract]

        contract_checker = icontract._checkers.find_checker(func=func)
        if contract_checker is not None:
            preconditions = contract_checker.__preconditions__
            snapshots = contract_checker.__postcondition_snapshots__

#
    # Preconditions and postconditions of __init__ of base classes are deliberately ignored (and not collapsed) since
    # initialization is an operation specific to the concrete class and does not relate to the class hierarchy.
    if key not in ['__init__']:
        base_preconditions = []  # type: List[List[Contract]]
        base_snapshots = []  # type: List[Snapshot]
        base_postconditions = []  # type: List[Contract]

        bases_have_func = False
        for base in bases:
            if hasattr(base, key):
                bases_have_func = True

                # Check if there is a checker function in the base class
                base_func = getattr(base, key)
                base_contract_checker = icontract._checkers.find_checker(func=base_func)

                # Ignore functions which don't have preconditions or postconditions
                if base_contract_checker is not None:
                    base_preconditions.extend(base_contract_checker.__preconditions__)
                    base_snapshots.extend(base_contract_checker.__postcondition_snapshots__)
                    base_postconditions.extend(base_contract_checker.__postconditions__)

        # Collapse preconditions and postconditions from the bases with the the function's own ones
        preconditions = _collapse_preconditions(
            base_preconditions=base_preconditions,
            bases_have_func=bases_have_func,
            preconditions=preconditions,
            func=func)

        snapshots = _collapse_snapshots(base_snapshots=base_snapshots, snapshots=snapshots)

def __call__(self, func: CallableT) -> CallableT:
        """
        Add the postcondition to the list of postconditions of the function ``func``.

        The function ``func`` is decorated with a contract checker if there is no contract checker in
        the decorator stack.

        :param func: function to be wrapped
        :return: contract checker around ``func`` if no contract checker on the decorator stack, or ``func`` otherwise
        """
        if not self.enabled:
            return func

        # Find a contract checker
        contract_checker = icontract._checkers.find_checker(func=func)

        if contract_checker is not None:
            # Do not add an additional wrapper since the function has been already wrapped with a contract checker
            result = func
        else:
            # Wrap the function with a contract checker
            contract_checker = icontract._checkers.decorate_with_checker(func=func)
            result = contract_checker

        # Add the postcondition to the list of postconditions stored at the checker
        assert hasattr(contract_checker, "__postconditions__")
        assert isinstance(getattr(contract_checker, "__postconditions__"), list)
        getattr(contract_checker, "__postconditions__").append(self._contract)

        return result