def __init__(self, key=None, output_format='<STR_LIT>',<EOL>treat_info_as_error=True, indexing_type='<STR_LIT:date>', proxy=None):
if key is None:<EOL><INDENT>key = os.getenv('<STR_LIT>')<EOL><DEDENT>if not key or not isinstance(key, str):<EOL><INDENT>raise ValueError('<STR_LIT>'<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>'<STR_LIT>')<EOL><DEDENT>self.key = key<EOL>self.output_format = output_format<EOL>if self.output_format is '<STR_LIT>' and not _PANDAS_FOUND:<EOL><INDENT>raise ValueError("<STR_LIT>"<EOL>"<STR_LIT>"<EOL>"<STR_LIT>")<EOL><DEDENT>self.treat_info_as_error = treat_info_as_error<EOL>self._append_type = True<EOL>self.indexing_type = indexing_type<EOL>self.proxy = proxy or {}<EOL>
Initialize the class

        Keyword Arguments:
            key:  Alpha Vantage api key
            retries:  Maximum amount of retries in case of faulty connection or
                server not able to answer the call.
            treat_info_as_error: Treat information from the api as errors
            output_format:  Either 'json', 'pandas' os 'csv'
            indexing_type: Either 'date' to use the default date string given
            by the alpha vantage api call or 'integer' if you just want an
            integer indexing on your dataframe. Only valid, when the
            output_format is 'pandas'
            proxy: Dictionary mapping protocol or protocol and hostname to 
            the URL of the proxy.