Design Notes for the new Tkinter C Interface
This note currently contains original design notes (scribbled on a palm pilot one warm day in San Jose), and has not been checked against the actual implementation.
March 2000 | Fredrik LundhTypes
The new C interface defines a number of object types:
Interpreter
This type holds a pointer to a Tcl interpreter instance. It should have the same layout as the corresponding object in the current version of Tkinter.
PyTclObject
This is a Python type implementation that wraps a Tcl object.
struct {
TclObj* object;
} PyTclObject;
To create new PyTclObject instances, call the factory function with an ordinary Python object:
PyString -> TclStringObj PyInt -> TclIntegerObj or TclStringObj (if too large) PyFloat -> TclFloatObj PyTuple -> TclArrayObj (?)
All other objects are converted to string objects (using PyObject_Str).
PyTclCommand
This type wraps a pointer to a Tcl command, and the associated client data.
struct {
/* true if command uses object interface */
int use_obj_interface;
/* command/client pointer */
TclCmd* command;
void* client_data;
} PyTclCommandObject;
The factory function takes a command name, and looks it up using Tcl’s CommandInfo function. Note that this type doesn’t provide any additional methods; at this time, it’s main purpose is to provide information for the bound method type.
PyTclBoundMethodObject
This is a callable type which combines a PyTclCommandObject with a method name (as a PyTclObject string) and information on how to convert arguments and results.
struct {
PyTclCommandObject* command;
PyTclObject* method;
void* convert; /* to be defined */
} PyTclBoundMethodObject;
The call hook accepts an argument tuple and a keyword dictionary. The values in the tuple are converted to PyTclObject’s. Simplified:
def makeargs(av, kw):
size = 1 + len(av) + 2*len(kw)
argv = tuple(size)
argv[0] = method
i = 1
for v in av:
if v is PyTclObject:
argv[i] = v
else:
argv[i] = pytclobject(v)
i = i + 1
for k, v in kw:
argv[i] = "-" + k
if item is PyTclObject:
argv[i+1] = v
else:
argv[i+1] = pytclobject(v)
i = i + 2
result = command->command(command->client_data, argv)
return pytclobject(result)
To speed things up even further, we could use a dictionary mapping well-known option names to PyTclObject strings which *include* the leading hyphen.
New Tkinter Interface
The new Tkinter interface is data driven.
For each widget class, the interface uses a method table which is used by the getattr hook to create PyTclBoundMethod objects on the fly.
class Scale(Widget):
_tk_map = {
"get": (PyTclObject("get"), None),
"set": (PyTclObject("set"), None),
}
__getattr__ = Widget._tk_getattr
Global String Cache
The global string cache maps known Tkinter names (method names, and common option values as defined in the Tkconstants module) to Tcl string objects (PyTclObject).
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