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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 init_config(config_file=None):
 """ Initialize the configuration from a config file. The values in config_file will override those already loaded from the default configuration file (defaults.cfg, in current package). This method does not setup logging. @param config_file: The path to a configuration file. @type config_file: C{str} @raise ValueError: if the specified config_file could not be read. @see: L{init_logging} """

    global config

    if config_file and os.path.exists(config_file):
        read = config.read([config_file])
        if not read:
            raise ValueError(
                "Could not read configuration from file: %s" % config_file)