cdsapi retrieval helper

[hsteptoe]

Description

A new function to help populate fields within the cdsapi retrieve() function. Mainly to make dealing with date ranges quicker. The function would take a from and to date, and options to specify variables and time interval (frequency). This could be extended to use dask for parallel retrievals.

Example syntax

VARS = ['10m_u_component_of_wind', '10m_v_component_of_wind']
getera5(from='2019-05-23', to='2019-05-30', var=VARS, freq='H')

or for a parallel version

FROMS=['2019-05-23', '2008-12-25']
TOS = ['2019-05-30', '2009-01-05']
VARS = ['10m_u_component_of_wind', '10m_v_component_of_wind']
getera5(from=FROMS, to=TOS, var=VARS, freq='H')

to retrieve different time means for the same period

getera5(from=['2019-05-23', '2019-05-23'], to= ['2019-05-30', '2019-05-30'], 
        var=VARS, freq=['H', 'M'])

Notes

• In the case of multiple retrievals, the function would assume that the same VARS are retrieved in each case. I can't particularly see a use case where different vars would be wanted for different time periods within code relating to one project...
• Dependencies: pandas to deal with date range wrangling
• I'd suggest sticking with the pandas frequency aliases: https://pandas.pydata.org/pandas-docs/stable/user_guide/timeseries.html#timeseries-offset-aliases
• Need to consider what other args might be need to facilitate the full range of cdsapi retrievals