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Understanding How Python Scripts are Invoked

It is important to understand a few facts about how Python scripts are invoked within Chameleon to understand how the mechanism works:

• Firstly, variables created in Python within the VMD file are in a global namespace for the Engine object (in the case of your application), or the channel while it is running (in the case of Iguana). If you create a variable XYZ in one script the value of that variable can be accessed elsewhere in other scripts. The lifetime of the variables is equal to that of the Chameleon engine instance that contains them (in the case of your application), or the channel while it is running (in the case of Iguana). For this reason, when using auto-acknowledgment in your application it is important that only one program thread can use an instance of a given Chameleon engine while generating an acknowledgment.

• Secondly, when each python script is fired, there is a special variable called 'value' that is mapped to the value of the field that this script is for.

For example:

When the MSH outgoing script of field 9 is fired, the value variable is used to set the contents of field 9 of the MSH segment of the message being generated.

When the MSH inbound script for field 5 is fired, the value variable contains the contents of field 5 of the MSH segment of the message being parsed.

Finally, an important concept to understand is the difference between parsing and generating messages. The inbound scripts are fired during the parsing of a message (during the parsing of the message for which you are attempting to generate an ACK message for). The outbound scripts are fired during the generation of a message; that is, during the generation of an ACK message.