A Simple Python Example
Overview
The following Python service prepends a greeting message to the selected text. This is a trivial example in that there is no GUI interaction, does not utilize any additional Python libraries, nor does it deal with multiple pasteboard types. It does, however, illustrate the basic points to consider when implementing services with Python.
A Simple Example: Prepend Greeting
The following code listing shows a complete Bellhop service script written in the Python language. You can try this yourself by simply creating a Bellhop document, adding a new Python service, and then pasting the following code directly into the editor window. Then all you have to do is activate the service using the Settings panel, and then you can invoke it from any services-aware application.
# Sample Python service to prepend a greeting to the selected text. This # service might be labeled "Prepend Greeting" in the Services menu. # The aPasteboard argument identifies the unique pasteboard name # that is reserved for the current service transaction. You will # use this name as the argument to the various methods that get # and set data from the pasteboard. def runService (aPasteboard): # read from pasteboard theString = pasteboard.readstring(aPasteboard, NSStringPboardType) # format new string by adding greeting theString = 'Greetings from Python: ' + theString # write new string back to pboard pasteboard.declaretypes(aPasteboard, [NSStringPboardType]) pasteboard.writestring(aPasteboard, NSStringPboardType, theString)
Listing 1: Sample Python service
If you are familiar with the concepts and implementation details regarding system services in Mac OS X, the above script should be straightforward. If not, you can refer to the Apple developer documentation covering System Services and the More Info section of this document.
Looking at Listing 1, the first non-comment line is
def runService (aPasteboard):
The following lines read the selection from the service pasteboard:
# read from pasteboard theString = pasteboard.readstring(aPasteboard, NSStringPboardType)
Next we manipulate the pasteboard data to modify it. We are simply going to add a greeting:
# format new string by adding greeting theString = 'Greetings from Python:' + theString
Finally, we must write the modified data back to the pasteboard so that it is made available to the requesting application:
# Write new string back to pboard pasteboard.declaretypes(aPasteboard, [NSStringPboardType]) pasteboard.writestring(aPasteboard, NSStringPboardType, theString)
These lines first inform aPasteboard (our unique service pasteboard) that we are about to provide it with string data. Then we actually write the modified string to aPasteboard. Again, notice that we are using the custom Bellhop pasteboard extension to deal with the Mac OS X pasteboard.