Sophie: PyQt-2.5-1mdk i586

PyQt-2.5-1mdk.i586.rpm

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>Python Bindings for Qt (v2.5)</TH
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><H1
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><A
NAME="AEN116"
>General Limitations</A
></H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118"
>Python Strings, Qt Strings and Unicode</A
></H2
><P
>Unicode support was added to Qt in v2.0 and to Python in v1.6.  In Qt, Unicode
support is implemented using the <TT
CLASS="LITERAL"
>QString</TT
> class.  It is
important to understand that <TT
CLASS="LITERAL"
>QString</TT
>s, Python string objects
and Python Unicode objects are all different but conversions between them are
automatic in many cases and easy to achieve manually when needed.</P
><P
>Whenever PyQt expects a <TT
CLASS="LITERAL"
>QString</TT
> as a function argument, a
Python string object or a Python Unicode object can be provided instead, and
PyQt will do the necessary conversion automatically.</P
><P
>You may also manually convert Python string and Unicode objects to
<TT
CLASS="LITERAL"
>QString</TT
>s by using the <TT
CLASS="LITERAL"
>QString</TT
> constructor
as demonstrated in the following code fragment.</P
><TABLE
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><TD
><PRE
CLASS="PROGRAMLISTING"
>qs1 = QString('Converted Python string object')
qs2 = QString(u'Converted Python Unicode object')</PRE
></TD
></TR
></TABLE
><P
>In order to convert a <TT
CLASS="LITERAL"
>QString</TT
> to a Python string object use
the Python <TT
CLASS="LITERAL"
>str()</TT
> function.  Applying
<TT
CLASS="LITERAL"
>str()</TT
> to a null <TT
CLASS="LITERAL"
>QString</TT
> and an empty
<TT
CLASS="LITERAL"
>QString</TT
> both result in an empty Python string object.</P
><P
>In order to convert a <TT
CLASS="LITERAL"
>QString</TT
> to a Python Unicode object use
the Python <TT
CLASS="LITERAL"
>unicode()</TT
> function.  Applying
<TT
CLASS="LITERAL"
>unicode()</TT
> to a null <TT
CLASS="LITERAL"
>QString</TT
> and an empty
<TT
CLASS="LITERAL"
>QString</TT
> both result in an empty Python Unicode object.</P
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><DIV
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><H2
CLASS="SECT2"
><A
NAME="AEN141"
>Access to Protected Member Functions</A
></H2
><P
>When an instance of a C++ class is not created from Python it is not possible
to access the protected member functions, or emit the signals, of that
instance.  Attempts to do so will raise a Python exception.  Also, any Python
methods corresponding to the instance's virtual member functions will never be
called.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN144"
>Garbage Collection</A
></H2
><P
>C++ does not garbage collect unreferenced class instances, whereas Python does.
In the following C++ fragment both colours exist even though the first can no
longer be referenced from within the program:</P
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>c = QColor();
c = QColor();</PRE
></TD
></TR
></TABLE
><P
>In the corresponding Python fragment, the first colour is destroyed when
the second is assigned to <TT
CLASS="LITERAL"
>c</TT
>:</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>c = QColor()
c = QColor()</PRE
></TD
></TR
></TABLE
><P
>In Python, each colour must be assigned to different names.  Typically this
is done within class definitions, so the code fragment would be something like:</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>self.c1 = QColor()
self.c2 = QColor()</PRE
></TD
></TR
></TABLE
><P
>Sometimes a Qt class instance will maintain a pointer to another instance and
will eventually call the destructor of that second instance. The most common
example is that a <TT
CLASS="LITERAL"
>QObject</TT
> (and any of its sub-classes) keeps
pointers to its children and will automatically call their destructors. In
these cases, the corresponding Python object will also keep a reference to the
corresponding child objects.</P
><P
>So, in the following Python fragment, the first <TT
CLASS="LITERAL"
>QLabel</TT
> is
not destroyed when the second is assigned to <TT
CLASS="LITERAL"
>l</TT
> because the
parent <TT
CLASS="LITERAL"
>QWidget</TT
> still has a reference to it.</P
><TABLE
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><TD
><PRE
CLASS="PROGRAMLISTING"
>p = QWidget()
l = QLabel('First label',p)
l = QLabel('Second label',p)</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN160"
>C++ Variables</A
></H2
><P
>Access to C++ variables is supported.  They are accessed as Python instance
variables.  For example:</P
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><TD
><PRE
CLASS="PROGRAMLISTING"
>tab = QTab()
tab.label = "First Tab"
tab.r = QRect(10,10,75,30)</PRE
></TD
></TR
></TABLE
><P
>Global variables and static class variables are effectively read-only.  They
can be assigned to, but the underlying C++ variable will not be changed.  This
may change in the future.</P
><P
>Access to protected C++ class variables is not supported.  This may change in
the future.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN166"
>Multiple Inheritance</A
></H2
><P
>It is not possible to define a new Python class that sub-classes from more than
one Qt class.</P
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