Error drawing text on NSImage in PyObjC - cocoa

Question

I'm trying to overlay an image with some text using PyObjC, while striving to answer my question, "Annotate images using tools built into OS X". By referencing CocoaMagic, a RubyObjC replacement for RMagick, I've come up with this:
#!/usr/bin/env python
from AppKit import *
source_image = "/Library/Desktop Pictures/Nature/Aurora.jpg"
final_image = "/Library/Desktop Pictures/.loginwindow.jpg"
font_name = "Arial"
font_size = 76
message = "My Message Here"
app = NSApplication.sharedApplication() # remove some warnings
# read in an image
image = NSImage.alloc().initWithContentsOfFile_(source_image)
image.lockFocus()
# prepare some text attributes
text_attributes = NSMutableDictionary.alloc().init()
font = NSFont.fontWithName_size_(font_name, font_size)
text_attributes.setObject_forKey_(font, NSFontAttributeName)
text_attributes.setObject_forKey_(NSColor.blackColor, NSForegroundColorAttributeName)
# output our message
message_string = NSString.stringWithString_(message)
size = message_string.sizeWithAttributes_(text_attributes)
point = NSMakePoint(400, 400)
message_string.drawAtPoint_withAttributes_(point, text_attributes)
# write the file
image.unlockFocus()
bits = NSBitmapImageRep.alloc().initWithData_(image.TIFFRepresentation)
data = bits.representationUsingType_properties_(NSJPGFileType, nil)
data.writeToFile_atomically_(final_image, false)
When I run it, I get this:
Traceback (most recent call last):
File "/Users/clinton/Work/Problems/TellAtAGlance/ObviouslyTouched.py", line 24, in <module>
message_string.drawAtPoint_withAttributes_(point, text_attributes)
ValueError: NSInvalidArgumentException - Class OC_PythonObject: no such selector: set
Looking in the docs for drawAtPoint:withAttributes:, it says, "You should only invoke this method when an NSView has focus." NSImage is not a subclass of NSView, but I would hope this would work, and something very similar seems to work in the Ruby example.
What do I need to change to make this work?
I rewrote the code, converting it faithfully, line for line, into an Objective-C Foundation tool. It works, without problems. [I would be happy to post if here if there is a reason to do so.]
The question then becomes, how does:
[message_string drawAtPoint:point withAttributes:text_attributes];
differ from
message_string.drawAtPoint_withAttributes_(point, text_attributes)
? Is there a way to tell which "OC_PythonObject" is raising the NSInvalidArgumentException?

Answer 1

Here are the problems in the above code:
text_attributes.setObject_forKey_(NSColor.blackColor, NSForegroundColorAttributeName)
->
text_attributes.setObject_forKey_(NSColor.blackColor(), NSForegroundColorAttributeName)
bits = NSBitmapImageRep.alloc().initWithData_(image.TIFFRepresentation)
data = bits.representationUsingType_properties_(NSJPGFileType, nil)
->
bits = NSBitmapImageRep.imageRepWithData_(image.TIFFRepresentation())
data = bits.representationUsingType_properties_(NSJPEGFileType, None)
Minor typos indeed.
Note that the middle portion of the code can be replaced with this more-readable variant:
# prepare some text attributes
text_attributes = {
NSFontAttributeName : NSFont.fontWithName_size_(font_name, font_size),
NSForegroundColorAttributeName : NSColor.blackColor()
}
# output our message
NSString.drawAtPoint_withAttributes_(message, (400, 400), text_attributes)
I learned this by looking at the source code to NodeBox, the twelve lines of psyphography.py and cocoa.py, particularly the save and _getImageData methods.