<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def typecheck(self, t):
 """Create a typecheck from some value ``t``. This behaves differently depending on what ``t`` is. It should take a value and return True if the typecheck passes, or False otherwise. Override ``pre_validate`` in a child class to do type coercion. * If ``t`` is a type, like basestring, int, float, *or* a tuple of base types, then a simple isinstance typecheck is returned. * If ``t`` is a list or tuple of instances, such as a tuple or list of integers or of strings, it's treated as the definition of an enum and a simple "in" check is returned. * If ``t`` is callable, ``t`` is assumed to be a valid typecheck. * If ``t`` is None, a typecheck that always passes is returned. If none of these conditions are met, a TypeError is raised. """

        if t is None:
            return lambda x: True

        def _isinstance(types, value):
            return isinstance(value, types)

        def _enum(values, value):
            return value in values

        if t.__class__ is type:
            return partial(_isinstance, t)
        elif isinstance(t, (tuple, list)):
            if all([x.__class__ is type for x in t]):
                return partial(_isinstance, t)
            return partial(_enum, t)
        elif callable(t):
            return t
        raise TypeError('%r is not a valid field type' % r)