Improve build_base_energy_totals.py

[hazemakhalek]

Refactoring and code optimization is needed in the script

Building on the reviews of PR #317, the following enhancements can be introduced to the script

The two sections can be made more efficient using a simple loop, or similar ideas.

pypsa-earth-sec/scripts/build_base_energy_totals.py

Lines 63 to 78 in b0cee2a

	if df_sector.empty:
	if sector == "consumption by households":
	energy_totals_base.at[country, "electricity residential"] = np.NaN
	energy_totals_base.at[country, "residential oil"] = np.NaN
	energy_totals_base.at[country, "residential biomass"] = np.NaN
	energy_totals_base.at[country, "residential gas"] = np.NaN
	energy_totals_base.at[country, "total residential space"] = np.NaN
	energy_totals_base.at[country, "total residential water"] = np.NaN
	elif sector == "services":
	energy_totals_base.at[country, "services electricity"] = np.NaN
	energy_totals_base.at[country, "services oil"] = np.NaN
	energy_totals_base.at[country, "services biomass"] = np.NaN
	energy_totals_base.at[country, "services gas"] = np.NaN
	energy_totals_base.at[country, "total services space"] = np.NaN
	energy_totals_base.at[country, "total services water"] = np.NaN

pypsa-earth-sec/scripts/build_base_energy_totals.py

Lines 214 to 244 in 31a3354

	energy_totals_base.at[country, "road biomass"] = round(
	df_sector[
	df_sector.Commodity.isin(biomass_fuels)
	].Quantity_TWh.sum(),
	4,
	)
	energy_totals_base.at[country, "road oil"] = round(
	df_sector[df_sector.Commodity.isin(oil_fuels)].Quantity_TWh.sum(), 4
	)
	elif sector == "agriculture":
	energy_totals_base.at[country, "agriculture electricity"] = round(
	df_sector[
	(df_sector.Commodity == "Electricity")
	].Quantity_TWh.sum(),
	4,
	)
	energy_totals_base.at[country, "agriculture oil"] = round(
	df_sector[df_sector.Commodity.isin(oil_fuels)].Quantity_TWh.sum(), 4
	)
	energy_totals_base.at[country, "agriculture biomass"] = round(
	df_sector[
	df_sector.Commodity.isin(biomass_fuels)
	].Quantity_TWh.sum(),
	4,
	)
	energy_totals_base.at[country, "agriculture coal"] = round(
	df_sector[df_sector.Commodity.isin(coal_fuels)].Quantity_TWh.sum(),
	4,
	)
	# energy_totals_base.at[country, "electricity rail"] = round(df_house[(df_house.Commodity=="Electricity")].Quantity_TWh.sum(), 4)

Please give a clear and concise description and provide context why the feature would be useful.
Also, we'd appreciate any implementation ideas and references you already have.