How to use the icontract._types.Snapshot function in icontract

The default is to always capture the snapshot unless the interpreter runs in optimized mode (``-O`` or
            ``-OO``).

        """
        self._snapshot = None  # type: Optional[Snapshot]
        self.enabled = enabled

        # Resolve the snapshot only if enabled so that no overhead is incurred
        if enabled:
            location = None  # type: Optional[str]
            tb_stack = traceback.extract_stack(limit=2)[:1]
            if len(tb_stack) > 0:
                frame = tb_stack[0]
                location = 'File {}, line {} in {}'.format(frame.filename, frame.lineno, frame.name)

            self._snapshot = Snapshot(capture=capture, name=name, location=location)

require = icontract._decorators.require
snapshot = icontract._decorators.snapshot
ensure = icontract._decorators.ensure
invariant = icontract._decorators.invariant

import icontract._globals
aRepr = icontract._globals.aRepr
SLOW = icontract._globals.SLOW

import icontract._metaclass
DBCMeta = icontract._metaclass.DBCMeta
DBC = icontract._metaclass.DBC

import icontract._types
_Contract = icontract._types.Contract
_Snapshot = icontract._types.Snapshot

import icontract.errors
ViolationError = icontract.errors.ViolationError

contract_checker = icontract._checkers.find_checker(func=func)

        if contract_checker is None:
            raise ValueError("You are decorating a function with a snapshot, but no postcondition was defined "
                             "on the function before.")

        assert self._snapshot is not None, "Expected the enabled snapshot to have the property ``snapshot`` set."

        # Add the snapshot to the list of snapshots stored at the checker
        assert hasattr(contract_checker, "__postcondition_snapshots__")

        snapshots = getattr(contract_checker, "__postcondition_snapshots__")
        assert isinstance(snapshots, list)

        for snap in snapshots:
            assert isinstance(snap, Snapshot)
            if snap.name == self._snapshot.name:
                raise ValueError("There are conflicting snapshots with the name: {!r}".format(snap.name))

        snapshots.append(self._snapshot)

        return func