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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_config(config_schema, env=None):
 """Parse config from the environment against a given schema Args: config_schema: A dictionary mapping keys in the environment to envpy Schema objects describing the expected value. env: An optional dictionary used to override the environment rather than getting it from the os. Returns: A dictionary which maps the values pulled from the environment and parsed against the given schema. Raises: MissingConfigError: A value in the schema with no default could not be found in the environment. ParsingError: A value was found in the environment but could not be parsed into the given value type. """

    if env is None:
        env = os.environ

    return parser.parse_env(
        config_schema,
        env,
    )