Python Interface to MAPL

This document presents a very high level description of a python interface to MAPL.

GEOS-5 Use Cases

The examples below are based on the actual GEOS-5 GCM Application, and a few components at the very top of the hierarchy. Here we assumed that MAPL Grid Components can be implemented entirely in C/Fortran or in Python.

GEOS-5 Application with Fortran Root Component

In this example of a GEOS-5 application written in Python, the very top root component is implemented entirely in a shared library.

import MAPL

if __name == "__main__":
 
#   Instantiate the root component
#   ------------------------------
    gcs = MAPL.GridComp(lib='/some/path/libGEOSana.so')
 
#   Instantiate MAPL
#   ----------------
    mapl = MAPL(root=gcs)
 
#   Run the cap
#   -----------
    mapl.go()

GEOS-5 Application with Python Root Component

In this example, the very top root component is now implemented in Python.

import MAPL
import GEOSgcs  # the GEOSgcs component is implemented here

if __name == "__main__":

#   Instantiate the Python root component
#   -------------------------------------
    gcs = GEOSgcs(rc='gcs.rc')

#   Instantiate MAPL
#   ----------------
    mapl = MAPL(root=gcs)

#   Run the cap
#   -----------
    mapl.go()

A python component with Children implemented in Fortran

In this example, the GEOSgcs component is implemented in Python, with its children, components ANA and GCM, implemented in Fortran. Notice that every component should be subclass of MAPL_GridComp.

import MAPL

class GridComp(MAPL.GridComp):
    """
    Implements the GEOSgcs component by subclassing MAPL.GridComp.
    """

    def SetServices(self):
        """
        SetServices for a composite component.
        """
 
#       Instantiate Children component
#       ------------------------------
        ana = MAPL.GridComp(lib='/some/path/libGEOSana.so')
        gcm = MAPL.GridComp(lib='/some/path/libGEOSgcm.so')

#       Adopt children
#       --------------
        self.AddChild(ana)
        self.AddChild(gcm)

#       Set connectivity among children
#       -------------------------------
        vars = ('Tinc', 'Sinc', 'Uinc', 'Vinc', 'SSHinc' )
        self.AddConnectivity(src=[ana,vars], dst=[gcm,vars])
        self.AddConnectivity(src=[gcm,'LWI'], dst=[ana,'ORO'])

#       Run the base class SetServices
#       ------------------------------
        MAPL.GridComp.__SetServices__(self)

Notice that the standard Initialize(), Run() and Finalize() methods are inherited from the base class MAPL.GridComp.

A python component with Children implemented in Python

In this example, the GEOSgcs component is implemented in Python, with its children, components ANA and GCM, also implemented in Python.

import MAPL
import GEOSana
import GEOSgcm

class GridComp(MAPL.GridComp):
    """
    Implements the GEOSgcs component by subclassing MAPL.GridComp.
    """
 
    def SetServices(self):
        """
        SetServices for a composite component.
        """
  
#       Instantiate Children component
#       ------------------------------
        ana = GEOSana()
        gcm = GEOSgcm()
 
#       Adopt children
#       --------------
        self.AddChild(ana)
        self.AddChild(gcm)

#       Set connectivity among children
#       -------------------------------
        vars = ('Tinc', 'Sinc', 'Uinc', 'Vinc', 'SSHinc' )
        self.AddConnectivity(src=[ana,vars], dst=[gcm,vars])
        self.AddConnectivity(src=[gcm,'LWI'], dst=[ana,'ORO'])

#       Run the base class SetServices
#       ------------------------------
        MAPL.GridComp.__SetServices__(self)

In this case we implement the standard Run() method, but inherit Initialize() and Finalize() from the base class MAPL.GridComp

    def Run(self):
        """
        Implementation of a simple run method.
        """
       
#       Run the base class method
#       -------------------------
        MAPL.GridComp.__Run__(self)

#       Retrieve some data from a state
#       -------------------------------
        uwnd, vwnd, = self.Export.GetPointer(['UWND', 'VWND'])

#       Just print it
#       -------------
        print "u-wind = ", uwnd.min(), uwnd.max()
        print "v-wind = ", vwnd.min(), vwnd.max()