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Python Cookbook by David Ascher, Alex Martelli

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Supporting Multiple Values per Row in a Tkinter Listbox

Credit: Brent Burley

Problem

You need a Tkinter widget that works just like a normal Listbox but with multiple values per row.

Solution

When you find a functional limitation in Tkinter, most often the best solution is to build your own widget as a Python class, subclassing an appropriate existing Tkinter widget (often Frame, so you can easily aggregate several native Tkinter widgets into your own compound widget) and extending and tweaking its functionality when necessary. Rather than solving the problems of just one application, this gives you a reusable component that you can reuse in many applications. For example, here’s a way to make a multicolumn equivalent of a Tkinter Listbox:

from Tkinter import *

class MultiListbox(Frame):
    def _ _init_ _(self, master, lists):
        Frame._ _init_ _(self, master)
        self.lists = []
        for l,w in lists:
            frame = Frame(self); frame.pack(side=LEFT, expand=YES, fill=BOTH)
            Label(frame, text=l, borderwidth=1, relief=RAISED).pack(fill=X)
            lb = Listbox(frame, width=w, borderwidth=0, selectborderwidth=0,
                         relief=FLAT, exportselection=FALSE)
            lb.pack(expand=YES, fill=BOTH)
            self.lists.append(lb)
            lb.bind('<B1-Motion>', lambda e, s=self: s._select(e.y))
            lb.bind('<Button-1>', lambda e, s=self: s._select(e.y))
            lb.bind('<Leave>', lambda e: 'break')
            lb.bind('<B2-Motion>', lambda e, s=self: s._b2motion(e.x, e.y))
            lb.bind('<Button-2>', lambda e, s=self: s._button2(e.x, e.y))
        frame = Frame(self); frame.pack(side=LEFT, fill=Y)
        Label(frame, borderwidth=1, relief=RAISED).pack(fill=X)
        sb = Scrollbar(frame, orient=VERTICAL, command=self._scroll)
        sb.pack(expand=YES, fill=Y)
        self.lists[0]['yscrollcommand']=sb.set

    def _select(self, y):
        row = self.lists[0].nearest(y)
        self.selection_clear(0, END)
        self.selection_set(row)
        return 'break'

    def _button2(self, x, y):
        for l in self.lists: l.scan_mark(x, y)
        return 'break'

    def _b2motion(self, x, y):
        for l in self.lists: l.scan_dragto(x, y)
        return 'break'

    def _scroll(self, *args):
        for l in self.lists:
            apply(l.yview, args)

    def curselection(self):
        return self.lists[0].curselection(  )

    def delete(self, first, last=None):
        for l in self.lists:
            l.delete(first, last)

    def get(self, first, last=None):
        result = []
        for l in self.lists:
            result.append(l.get(first,last))
        if last: return apply(map, [None] + result)
        return result

    def index(self, index):
        self.lists[0].index(index)

    def insert(self, index, *elements):
        for e in elements:
            i = 0
            for l in self.lists:
                l.insert(index, e[i])
                i = i + 1

    def size(self):
        return self.lists[0].size(  )

    def see(self, index):
        for l in self.lists:
            l.see(index)

    def selection_anchor(self, index):
        for l in self.lists:
            l.selection_anchor(index)

    def selection_clear(self, first, last=None):
        for l in self.lists:
            l.selection_clear(first, last)

    def selection_includes(self, index):
        return self.lists[0].selection_includes(index)

    def selection_set(self, first, last=None):
        for l in self.lists:
            l.selection_set(first, last)

if _ _name_ _ == '_ _main_ _':
    tk = Tk(  )
    Label(tk, text='MultiListbox').pack(  )
    mlb = MultiListbox(tk, (('Subject', 40), ('Sender', 20), ('Date', 10)))
    for i in range(1000):
      mlb.insert(END, 
          ('Important Message: %d' % i, 'John Doe', '10/10/%04d' % (1900+i)))
    mlb.pack(expand=YES,fill=BOTH)
    tk.mainloop(  )

Discussion

This recipe shows a compound widget that gangs multiple Tk Listbox widgets to a single scrollbar to achieve a simple multicolumn scrolled listbox. Most of the Listbox API is mirrored to make the widget act like the normal Listbox, but with multiple values per row. The resulting widget is lightweight, fast, and easy to use. The main drawback is that only text is supported, which is a fundamental limitation of the underlying Listbox widget.

In this implementation, only single-selection is allowed, but it could be extended to multiple selection. User-resizable columns and auto-sorting by clicking on the column label should also be possible. Auto-scrolling while dragging Button-1 was disabled because it broke the synchronization between the lists. However, scrolling with Button-2 works fine.

One note about the implementation: in the MultiListbox._ _init_ _ method, several lambda forms are used as the callable second arguments (callbacks) of the bind method calls on the contained Listbox widgets. This is traditional, but if you share in the widespread dislike for lambda, note that lambda is never truly necessary. In this case, the easiest way to avoid the lambdas is to redefine all the relevant methods (_select, _button2, etc.) as taking two formal arguments (self, e) and extract the data they need from argument e. Then in the bind calls you can simply pass the bound self._select method, and so on.

See Also

Information about Tkinter can be obtained from a variety of sources, such as Pythonware’s An Introduction to Tkinter, by Fredrik Lundh (http://www.pythonware.com/library), New Mexico Tech’s Tkinter reference (http://www.nmt.edu/tcc/help/lang/python/docs.html), and various books.

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