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ACS Training

Developing Python Clients

NRAO - Socorro, July 2004 ACS Training 2

Python’s Pros

• Good stability

• Faster start-up time than Java

• Execution time usually sufficient, although not comparable to C++

• Fastest development time

• Fewer lines of code, easy to understand if not too complex

• Good for asynchronous, distributed testing

• Ideal to allow users (astronomers) to control program behavior through scripts


Python’s Cons

• No compile-time checking: code inconsistencies only discovered at run-time in forms of software errors

• Therefore not well suited for production software that has a large code base and gets maintained by different developers

• Free tool support not as good as for Java (profilers, remote debugging, IDEs, …)


What’s Available in Python?

• If it’s been implemented in the ACS C++ or Java APIs chances are it also exists in Python or no one has asked for it yet.

• Only major thing missing is XML support in the form of “helper” classes.


Very Simple Example

from Acspy.Clients.SimpleClient import PySimpleClient

simpleClient = PySimpleClient() #Make an instance of the PySimpleClientremoteComponent="MOUNT2_LOOP"

try: mount = simpleClient.getComponent(remoteComponent)

actAzProperty = mount._get_actAz() #Get the actAz property (azm, compl) = actAzProperty.get_sync() #Get the value of the property print "MOUNT actual azimuth: ", azm simpleClient.releaseComponent(remoteComponent)

except Exception, e: print "Sorry, maybe there was no",remoteComponent,"object" print "The exception was:", e

simpleClient.disconnect()


Callback Examplefrom Acspy.Clients.SimpleClient import PySimpleClient

import ACS, ACS__POA # Import the Python CORBA stubs for BACI

from time import sleep

class MyMonitor(ACS__POA.CBdouble):

'''This class defines method(s) that will be invoked asynchronously by the mount device'''

#------------------------------------------------------------------

def __init__ (self, propName = None):

if propName != None:

self.propName = propName

else:

self.propName = "NoName"

#------------------------------------------------------------------


Callback Example (continued)

def working (self, value, completion, desc): ''' Method that does all the real work. Parameters: value = the double we are interested in completion = completion structure desc = callback struct description ''' print "Working: ", str(self.propName), " is ", str(value) #------------------------------------------------------------------ def done (self, value, completion, desc): ''' Invoked just before a monitor is destroyed. Parameters: value = the final value of the double we are interested in completion = completion structure desc = callback struct description ''' print "Done: ", str(self.propName), " is ", str(value)



def negotiate (self, time_to_transmit, desc): '''For simplicities sake, we always return true. ''' return TRUE#--------------------------------------------------------------------

simpleClient = PySimpleClient()

try: mount = simpleClient.getComponent("MOUNT2_LOOP") actAzProperty = mount._get_actAz() #Get the actAz property cbMon = MyMonitor("actAz") #Create a callback monitor for actAz cbMonServant = cbMon._this() #Activate the callback monitor desc = ACS.CBDescIn(0L, 0L, 0L) #Create the real monitor actMon = actAzProperty.create_monitor(cbMonServant, desc) actMon.set_timer_trigger(10000000) #Working method once per sec. sleep(10) #Destroy the monitor after ten seconds actMon.destroy()



# Release the component

simpleClient.releaseComponent("MOUNT2_LOOP")

except Exception, e:

print "Sorry, I expected there to be a Mount in the system and"

print "there isn't."

print "The exception was:", e

simpleClient.disconnect()


What methods does PySimpleClient have?

Every Python Container Service method is

available in Python!!!

See the Pydoc documentation for the

ContainerServices class.

http://www.eso.org/~almamgr/AlmaAcs/OnlineDocs/ACS_docs/py/Acspy.Servants.ContainerServices.html


Python-related Makefile Targets

• PY_SCRIPTS - Specifies Python scripts without the .py extension that will be installed into $INTROOT/bin.

• PY_MODULES – Specifies Python modules with the .py extension that will be installed into $INTROOT/lib/python/site-packages.

• PY_PACKAGES – Specifies Python packages to be installed into $INTROOT/lib/python/site-packages. Really these are just directories containing Python scripts.


Questions about Python Clients???


Demo

atacamalargemillimeterarray acs training developing python clients

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