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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_env_variable(var_name, default=None):
 """Get the environment variable or raise exception."""

    try:
        return os.environ[var_name]
    except KeyError:
        if default is not None:
            return default
        else:
            error_msg = 'The environment variable {} was missing, abort...'\
                        .format(var_name)
            raise EnvironmentError(error_msg)