Working with Variables

A compute module’s input and output variables are organized into groups. You can find group names and other information about variables in the documentation of each compute module in List of SSC Compute Modules.

Input variables have a “Required” property, while output variables do not. Some compute modules have an “Output” or “SystemOutput” group for output variables.

An “inout” variable is both an input and an output to the compute module. If an inout variable is required, you must assign it a value along with the other inputs. For example, gen is both an input to the Battery module and an output.

The following code examples show how to get and set a variable’s value, and how to work with groups.

For these examples, first import and create an instance of the Pvwattsv8 module with default values for the PVWatts – No Financial configuration:

import PySAM.Pvwattsv8 as pv

system_model = pv.default('PVWattsNone')

Get a variable’s value

There are three ways to get a variables value:

1. Access variables directly with <class>.<subclass>.<variable>.

   For example, to get the value of array_type variable, which is in the SystemDesign group:

   x = system_model.SystemDesign.array_type
   print(x)
   

2. Use the get attributes function getattr():

   group_object = getattr(system_model,'SystemDesign')
   variable = getattr(group_object,'array_type')
   print(group_object)
   print(variable)
   
   # equivalent with one line of code
   print( getattr(getattr(system_model, 'SystemDesign'), 'array_type') )
   

3. Use value(), which does not require the group name:

   x = system_model.value('array_type')
   print(x)
   

Set a variable value

1. Use setattr():

   old_array_type = system_model.SystemDesign.array_type
   new_array_type = 0
   
   system_design_group_object = getattr(system_model,'SystemDesign')
   setattr(system_design_group_object, 'array_type', new_array_type )
   
   print(old_array_type)
   print(system_model.SystemDesign.array_type)
   

2. Use value():

   old_array_type = system_model.SystemDesign.array_type
   new_array_type = 0
   
   system_model.value('array_type', new_array_type);
   
   print(old_array_type)
   print(system_model.SystemDesign.array_type)
   

Get and Set Variable Values by Group

Use the assign() and export() functions to work with groups.

To get a dictionary of all variables in a group, use export():

x = system_model.SystemDesign.export()
print(x)

Use assign() to set variable values by group. For example, this code first uses export() to get a dictionary x of variables in the SystemDesign group so you can see what the group variables and values are. It then uses assign() to change the value of the azimuth and gcr variables in that group, and gets a new dictionary y:

x = system_model.SystemDesign.export()
print(x)

inputs_to_change = {'azimuth':100, 'gcr': .5}
system_model.SystemDesign.assign(inputs_to_change)

y = system_model.SystemDesign.export()
print(y)