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      type-checking done. </P
><P
>Python signals are indicated by the
      <TT
CLASS="FUNCTION"
>PYSIGNAL()</TT
> function, which also takes a
      string. There is no <TT
CLASS="FUNCTION"
>PYSLOT()</TT
> function
      corresponding to <TT
CLASS="FUNCTION"
>SLOT()</TT
>, because you can
      use <SPAN
><I
CLASS="EMPHASIS"
>any</I
></SPAN
> function as a slot in
      Python.</P
><P
>The argument of <TT
CLASS="FUNCTION"
>PYSIGNAL()</TT
> is a simple
      string that is unique for the class from which the signal is
      emitted. It performs the same function as the
      <SPAN
><I
CLASS="EMPHASIS"
>occasion</I
></SPAN
> string in the small
      <TT
CLASS="FILENAME"
>registry.py</TT
> script.  The difference is that
      <TT
CLASS="FUNCTION"
>PYSIGNAL()</TT
> string needs to be unique only
      for the class, and not the whole application.</P
><P
>Connecting to a Python signal doesn't
      differ much from connecting to a C++ signal, except that you
      don't have to worry so much about the type and number of
      arguments of the signal. To rewrite the
      <TT
CLASS="FILENAME"
>registry.py</TT
> example:</P
><DIV
CLASS="EXAMPLE"
></A
><P
><B
>Example 7-6. Python signals and slots</B
></P
><PRE
CLASS="PROGRAMLISTING"
>#
# sigslot.py  &#8212; python signals and slots
#
from qt import *

class Button(QObject):

    def clicked(self):
        self.emit(PYSIGNAL("sigClicked"), ())

class Application(QObject):

    def __init__(self):
        QObject.__init__(self)

        self.button=Button()
        self.connect(self.button, PYSIGNAL("sigClicked"),
                        self.doAppSpecificFunction)
        self.connect(self.button, PYSIGNAL("sigClicked"),
                        self.doSecondFunction)

    def doAppSpecificFunction(self):
        print "Function called"

    def doSecondFunction(self):
        print "A second function is called."

app=Application()
app.button.clicked()
      </PRE
></DIV
><P
>Running this example from the command line gives the
      following output:</P
><PRE
CLASS="SCREEN"
>/home/boudewijn/doc/pyqt/ch6 $ python sigslot.py
A second function is called.
Function called
    </PRE
><P
>The <TT
CLASS="CLASSNAME"
>Button</TT
> emits the
      Python signal. Note the construction: the second argument to the
      <TT
CLASS="FUNCTION"
>emit</TT
> function is a
      <SPAN
><I
CLASS="EMPHASIS"
>tuple</I
></SPAN
> that contains the arguments you want
      to pass on. It must always be a tuple, even if it has to be an
      empty tuple, or a tuple with only one element. This is shown in
      the next example, in which we have to explicitly create an empty
      tuple, and a tuple with one element from a single argument, by
      enclosing the argument in brackets and adding a comma:</P
><DIV
CLASS="EXAMPLE"
></A
><P
><B
>Example 7-7. Python signals and slots with arguments</B
></P
><PRE
CLASS="PROGRAMLISTING"
>#
# sigslot2.py  &#8212; python signals and slots with arguments
#
from qt import *

class Widget(QObject):

    def noArgument(self):
        self.emit(PYSIGNAL("sigNoArgument"), ())

    def oneArgument(self):
        self.emit(PYSIGNAL("sigOneArgument"), (1, ))

    def twoArguments(self):
        self.emit(PYSIGNAL("sigTwoArguments"), (1, "two"))

class Application(QObject):

    def __init__(self):
        QObject.__init__(self)

        self.widget = Widget()

        self.connect(self.widget, PYSIGNAL("sigNoArgument"),
                        self.printNothing)
        self.connect(self.widget, PYSIGNAL("sigOneArgument"),
                        self.printOneArgument)
        self.connect(self.widget, PYSIGNAL("sigTwoArguments"),
                        self.printTwoArguments)
        self.connect(self.widget, PYSIGNAL("sigTwoArguments"),
                        self.printVariableNumberOfArguments)

    def printNothing(self):
        print "No arguments"

    def printOneArgument(self, arg):
        print "One argument", arg

    def printTwoArguments(self, arg1, arg2):
        print "Two arguments", arg1, arg2

    def printVariableNumberOfArguments(self, *args):
        print "list of arguments", args

app=Application()
app.widget.noArgument()
app.widget.oneArgument()
app.widget.twoArguments()
      </PRE
></DIV
><P
>Note the usage of the *arg argument
      definition. This Python construct means that a variable length
      list of un-named arguments can be passed to a function. Thus
      <TT
CLASS="FUNCTION"
>printVariableNumberOfArguments(self, *args)</TT
>
      fits every signal that you care to connect it to.</P
><P
>It's an interesting test to run this script
      several times: you will notice that the order in which the
      signals generated by <TT
CLASS="FUNCTION"
>twoArguments()</TT
> arrive
      at their destination is not fixed. This means that if a signal
      is connected to two or more slots, the slots are not called in
      any particular order. However, if two signals are connected to
      two separate slots, then the slots are called in the order in
      which the signals are emitted.</P
><P
>The following combinations of arguments to the
      <TT
CLASS="FUNCTION"
>connect()</TT
> function are possible:</P
><DIV
CLASS="TABLE"
></A
><P
><B
>Table 7-1. Matrix of
        <TT
CLASS="CLASSNAME"
>QObject</TT
>.<TT
CLASS="FUNCTION"
>connect()</TT
>
        combinations.</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><THEAD
><TR
><TH
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>Signal
            </TH
><TH
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Connected to
            </TH
><TH
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              Syntax (Note that you can replace
              <TT
CLASS="FUNCTION"
>QObject.connect()</TT
> by
              <TT
CLASS="FUNCTION"
>self.connect()</TT
> everywhere.)
            </TH
></TR
></THEAD
><TBODY
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              C++
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ slot of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, SIGNAL("qtSignal()"), object2,
              SLOT("qtSlot()"))
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              C++
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ slot of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, SIGNAL("qtSignal()"), SLOT("qtSlot()"))
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              C++
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Python slot of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, SIGNAL("qtSignal()"), object2,
              pythonFunction)
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              C++
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Python slot of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, SIGNAL("qtSignal()"),
              self.pythonFunction)
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              C++
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ signal of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, SIGNAL("qtSignal()"), object2,
              SIGNAL("qtSignal()")
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              C++
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ signal of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, SIGNAL("qtSignal()"), self,
              SIGNAL("qtSignal()")
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ slot of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYSIGNAL("pySignal()"), object2,
              SLOT("qtSlot()"))

            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ slot of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYSIGNAL("pySignal()"),
              SLOT("qtSlot()"))
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Python slot of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYSIGNAL("pySignal()"),
              object2.pythonFunction))
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Python slot of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYTHON("pySignal()"),
              self.pythonFunction))
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ signal of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, OYSIGNAL("pySignal()"), object2,
              SIGNAL("qtSignal()")
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              C++ signal of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYSIGNAL("pySignal()"), self,
              SIGNAL("qtSignal()")
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Python signal of another object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYSIGNAL("pySignal()"), object2,
              PYSIGNAL("pySignal()")
            </TD
></TR
><TR
><TD
WIDTH="50"
ALIGN="LEFT"
VALIGN="TOP"
>              Python
            </TD
><TD
WIDTH="100"
ALIGN="LEFT"
VALIGN="TOP"
>              Python signal of &#8216;self' object
            </TD
><TD
WIDTH="100%"
ALIGN="LEFT"
VALIGN="TOP"
>              QObject.connect(object1, PYSIGNAL("pySignal()"),
              PYSIGNAL("pySignal()")
            </TD
></TR
></TBODY
></TABLE
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