What arguments does the Tkinter variable trace method callback function receive?

Callback Arguments for Tkinter Variable Trace Method

The Tkinter variable classes, such as StringVar() and BooleanVar(), provide a trace method that allows you to monitor changes to the variable's value. The callback function specified as the second argument to trace(mode, callback) receives four arguments: self, n, m, and x.

First Argument: Internal Variable Name

The first argument, self, is the internal variable name. This name can be passed to Tkinter's getvar() and setvar() methods. If you provide a name to the variable (e.g., StringVar(name='foo')), self will match that name. Otherwise, Tkinter will generate a name for you (e.g., PYVAR0).

Second Argument: Index or Empty String

For scalar variables, the second argument, n, will be an empty string. However, if the variable is a list variable (unlikely in Tkinter), n represents an index into the list.

Third Argument: Operation

The third argument, m, indicates the operation that triggered the callback. It can be "read," "write," or "unset."

Fourth Argument: Mode

The fourth argument, x, appears to be related to the mode specified in the trace method call. However, its exact significance is not well-documented.

Additional Information

*Tkinter is a Python wrapper around a Tcl/Tk interpreter. For more detailed information on variable traces, consult the official Tcl/Tk documentation: http://tcl.tk/man/tcl8.5/TclCmd/trace.htm#M14.

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