<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_propagator(name):
 """Retrieve a named propagator Args: name (str):
 Name of the desired propagator Return: Propagator class """


    from .sgp4 import Sgp4
    from .sgp4beta import Sgp4Beta

    scope = locals().copy()
    scope.update(globals())

    if name not in scope:
        raise UnknownPropagatorError(name)

    return scope[name]