ast wrote:
> Hello,
>
> import tkinter
> root = tkinter.Tk()
>
> Let's see all attributes of root:
>
>>>> root.__dict__
> {'master': None, 'children': {}, '_tclCommands': ['tkerror', 'exit',
> {'13825848destroy'], 'tk':
> <tkapp object at 0x02949C28>, '_tkloaded': 1}
>
> Now we change the background color using following command:
>>>> root['bg'] = 'red'
>
> I am wondering what 'bg' is for object root. Is it an attribute ?
>
>>>> root.__dict__
> {'master': None, 'children': {}, '_tclCommands': ['tkerror', 'exit',
> {'13825848destroy'], 'tk':
> <tkapp object at 0x02949C28>, '_tkloaded': 1}
>
> No, 'bg' is not in root attribute's list. So what is it ?
Let's drill down a bit:
>>> import tkinter, inspect
>>> print(inspect.getsource(tkinter.Tk.__setitem__))
def __setitem__(self, key, value):
self.configure({key: value})
>>> print(inspect.getsource(tkinter.Tk.configure))
def configure(self, cnf=None, **kw):
"""Configure resources of a widget.
The values for resources are specified as keyword
arguments. To get an overview about
the allowed keyword arguments call the method keys.
"""
return self._configure('configure', cnf, kw)
>>> print(inspect.getsource(tkinter.Tk._configure))
def _configure(self, cmd, cnf, kw):
"""Internal function."""
if kw:
cnf = _cnfmerge((cnf, kw))
elif cnf:
cnf = _cnfmerge(cnf)
if cnf is None:
return self._getconfigure(_flatten((self._w, cmd)))
if isinstance(cnf, str):
return self._getconfigure1(_flatten((self._w, cmd, '-'+cnf)))
self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
>>> print(inspect.getsource(root.tk.call))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.4/inspect.py", line 830, in getsource
lines, lnum = getsourcelines(object)
File "/usr/lib/python3.4/inspect.py", line 819, in getsourcelines
lines, lnum = findsource(object)
File "/usr/lib/python3.4/inspect.py", line 655, in findsource
file = getfile(object)
File "/usr/lib/python3.4/inspect.py", line 536, in getfile
'function, traceback, frame, or code object'.format(object))
TypeError: <built-in method call of tkapp object at 0x7f84ec9f3370> is not a
module, class, method, function, traceback, frame, or code object
OK, we've reached C code, from here more traditional methods of code
inspection are required.
tkinter is a wrapper for a GUI written in tcl/tk. For every GUI element in
tkinter there is a corresponding tcl object that holds the actual bg data.
It's just that at some point in the development of tkinter someone thought
that
widget["bg"] = "red"
is more convenient than
widget.configure(bg="red")
While it would have been possible to choose
widget.bg = "red"
that would have mixed the tcl and python namespaces. When the tcl object
acquires new attributes hilarity ensues...
(I probably would have chosen widget.gui.bg = "red")
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