<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def parse_env(config_schema, env):
 """Parse the values from a given environment against a given config schema Args: config_schema: A dict which maps the variable name to a Schema object that describes the requested value. env: A dict which represents the value of each variable in the environment. """

    try:
        return {
            key: item_schema.parse(key, env.get(key))
            for key, item_schema in config_schema.items()
        }
    except KeyError as error:
        raise MissingConfigError(
            "Required config not set: {}".format(error.args[0])
        )