Creating the Python Module

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Creating the Python Module

One useful feature of Chameleon is that the Python scripts that you write for your VMD files can reference external Python modules. This enables you to use the same code in multiple VMD files and Iguana channels without having to create multiple copies of it.

For example, the following Python module provides the functions you will need to detect whether messages of a particular type are not being transmitted:

import os
import stat
import time

# create global variables for message timestamps:
#        Timestamp contains the last time a message of this type was seen
#        WarningTime contains the last time a warning was sent for
#                    messages of this type
def startMessageChecking(paramMessageNames):
	global MessageNames
	global Timestamp
	global MessageCount
	global WarningTime
	MessageNames = paramMessageNames
	try:
    		Timestamp
	except NameError:
		# the following statements are needed to define the dictionaries;
		# otherwise, Python will flag this as an error
		Timestamp = {}
		MessageCount = {}
		WarningTime = {}
		# now that the dictionaries are defined, they can be initialized
		for MessageName in MessageNames:
			Timestamp[MessageName] = time.time()
			MessageCount[MessageName] = 0
			WarningTime[MessageName] = 0

# update the timestamp for this message and increment message counter
def touchMessage(MessageName):
	global Timestamp
	global MessageCount
    	Timestamp[MessageName] = time.time()
    	MessageCount[MessageName] += 1

# check each message type to see whether there is message activity
def checkForInactivity(InactivityTime, WarningFrequency):
	global MessageNames
	global Timestamp
	global MessageCount
	global WarningTime
    	CurrentTime = time.time()
    	for MessageName in MessageNames:
        	# check whether messages of this type have arrived recently
        	LastTime = Timestamp[MessageName]
        	Delta = int(CurrentTime - LastTime)
		if Delta > InactivityTime:
	   		# no message of this type has arrived recently; channel
	   		# inactivity has been detected
	   		#
           		# check whether a warning message has been sent recently
           		LastWarningTime = WarningTime[MessageName]
           		WarningDelta = int(CurrentTime - LastWarningTime)
           		if WarningDelta > WarningFrequency:
				# no warning message has been sent recently, so send one
				print "CHANNEL INACTIVITY WARNING:"
				if MessageCount[MessageName] > 0:
					LastString = time.strftime( '%Y-%m-%d %H:%M', \
							time.localtime(LastTime))
					print "No %s messages since %s" % \
							(MessageName, LastString)
				else:
					print "No %s messages ever" % MessageName
					# update the timestamp for warning messages
				WarningTime[MessageName] = CurrentTime

To use this Python code, you must:

Save this code in a file on your system named inactivemessage.py;
Ensure that Chameleon can find this file when it is searching for Python modules (see Searching for Modules for details on how to do this);
In your VMD file, write Python scripts that refer to the module defined by this file.

In the following section, you will create a VMD file that refers to this Python code. To get a copy of the Python module, follow this link: inactivemessage.py.

It is important to note that the name of the file is significant. In Python, the name of a module is the same as the name of the file in which it is contained. In addition, all modules must have a file suffix of .py.

For example, if your file is named mymodulename.py, your Python scripts will use one of the following statements to import the module:

import mymodulename

from mymodulename import *

For more information on importing Python modules, see Importing Modules.

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Creating the Python Module