Pandas input output

Allows creation of btable from a pandas DataFrame, for example:

client('CREATE BTABLE example FROM PANDAS', pandas_df = example)

Also outputs pandas DataFrame(s) by default, where appropriate, instead of pretty-print string or Python dict. If one BQL statement is submitted, a single DataFrame is returned. If multiple statements are submitted, a list of DataFrames is returned. 

To turn off pandas DataFrame output, set argument pandas_output = False. Pretty-printing the result is still on by default, but the string is never returned now.