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Python Cookbook by David Ascher, Alex Martelli

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Module: Building GTK GUIs Interactively

Credit: Brian McErlean

One of Python’s greatest strengths is that it allows you to try things interactively at the interpreter. Tkinter shares this strength, since you can create buttons, windows, and other widgets, and see them instantly on screen. You can click on buttons to activate callbacks and still be able to edit and add to the widgets from the Python command line.

While the Python GTK bindings are generally excellent, one of their flaws is that interactive development is not possible. Before anything is actually displayed, the gtk.mainloop function must be called, ending the possibility of interactive manipulation.

Example 9-1 simulates a Python interpreter while transparently letting the user use GTK widgets without requiring a call to mainloop, which is similar to how Tk widgets work. This version contains enhancements added by Christian Robottom Reis to add readline-completion support.

This program works by running the GTK main loop in a separate thread. The main thread is responsible only for reading lines input by the user and for passing these to the GTK thread, which deals with pending lines by activating a timeout. The resulting program is virtually identical to the Python interpreter, except that there is now no need to call gtk.mainloop for GTK event handling to occur.

Example 9-1. Building GTK GUIs interactively

import _ _builtin_ _, _ _main_ _
import codeop, keyword, gtk, os, re, readline, threading, traceback, signal, sys

def walk_class(klass):
    list = []
    for item in dir(klass):
        if item[0] != "_":
            list.append(item)

    for base in klass._ _bases_ _:
        for item in walk_class(base):
            if item not in list: list.append(item)

    return list

class Completer:
    def _ _init_ _(self, lokals):
        self.locals = lokals
        self.completions = keyword.kwlist + \
                            _ _builtins_ _._ _dict_ _.keys(  ) + \
                            _ _main_ _._ _dict_ _.keys(  )

    def complete(self, text, state):
        if state == 0:
            if "." in text:
                self.matches = self.attr_matches(text)
            else:
                self.matches = self.global_matches(text)
        try:
            return self.matches[state]
        except IndexError:
            return None

    def update(self, locs):
        self.locals = locs

        for key in self.locals.keys(  ):
            if not key in self.completions:
                self.completions.append(key)

    def global_matches(self, text):
        matches = []
        n = len(text)
        for word in self.completions:
            if word[:n] == text:
                matches.append(word)
        return matches

    def attr_matches(self, text):
        m = re.match(r"(\w+(\.\w+)*)\.(\w*)", text)
        if not m:
            return
        expr, attr = m.group(1, 3)

        obj = eval(expr, self.locals)
        if str(obj)[1:4] == "gtk":
            words = walk_class(obj._ _class_ _)
        else:
            words = dir(eval(expr, self.locals))

        matches = []
        n = len(attr)
        for word in words:
            if word[:n] == attr:
                matches.append("%s.%s" % (expr, word))
        return matches

class GtkInterpreter(threading.Thread):
    """ Run a GTK mainloop(  ) in a separate thread. Python commands can be passed to the
    TIMEOUT = 100 # interval in milliseconds between timeouts

    def _ _init_ _(self):
        threading.Thread._ _init_ _ (self)
        self.ready = threading.Condition (  )
        self.globs = globals (  )
        self.locs = locals (  )
        self._kill = 0
        self.cmd = ''       # current code block
        self.new_cmd = None # waiting line of code, or None if none waiting

        self.completer = Completer(self.locs)
        readline.set_completer(self.completer.complete)
        readline.parse_and_bind('tab: complete')

    def run(self):
        gtk.timeout_add(self.TIMEOUT, self.code_exec)
        gtk.mainloop(  )

    def code_exec(self):
        """ Execute waiting code. Called every timeout period. """
        self.ready.acquire(  )
        if self._kill: gtk.mainquit(  )
        if self.new_cmd != None:
            self.ready.notify(  )
            self.cmd = self.cmd + self.new_cmd
            self.new_cmd = None
            try:
                code = codeop.compile_command(self.cmd[:-1])
                if code:
                    self.cmd = ''
                    exec code, self.globs, self.locs
                    self.completer.update(self.locs)
            except:
                traceback.print_exc(  )
                self.cmd = ''

        self.ready.release(  )
        return 1

    def feed(self, code):
        """ Feed a line of code to the thread. This function will block until the code is
        if code[-1:]!='\n': code = code +'\n' # raw_input strips newline
        self.completer.update(self.locs)
        self.ready.acquire(  )
        self.new_cmd = code
        self.ready.wait(  )  # Wait until processed in timeout interval
        self.ready.release(  )

        return not self.cmd

    def kill(self):
        """ Kill the thread, returning when it has been shut down. """
        self.ready.acquire(  )
        self._kill=1
        self.ready.release(  )
        self.join(  )

# Read user input in a loop and send each line to the interpreter thread

def signal_handler(*args):
    print "SIGNAL:", args
    sys.exit(  )

if _ _name_ _=="_ _main_ _":
    signal.signal(signal.SIGINT, signal_handler)
    signal.signal(signal.SIGSEGV, signal_handler)

    prompt = '>>> '
    interpreter = GtkInterpreter(  )
    interpreter.start(  )
    interpreter.feed("from gtk import *")
    interpreter.feed("sys.path.append('.')")
    if len (sys.argv) > 1:
        for file in open(sys.argv[1]).readlines(  ):
            interpreter.feed(file)
    print 'Interactive GTK Shell'

    try:
        while 1:
            command = raw_input(prompt) + '\n' # raw_input strips newlines
            prompt = interpreter.feed(command) and '>>> ' or '... '
    except (EOFError, KeyboardInterrupt): pass

    interpreter.kill(  )
    print

See Also

PyGTK is described and available at http://www.daa.com.au/~james/pygtk.

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