title: Error when trying to subclass gdb.Breakpoint while writing PythonGDB extension
body: <p>I'm trying to write a simple python extension for GDB that outputs to a file whenever a breakpoint is hit. According to the documentation, "The gdb.Breakpoint class can be sub-classed" (see <a href="http://sourceware.org/gdb/onlinedocs/gdb/Breakpoints-In-Python.html" rel="nofollow">http://sourceware.org/gdb/onlinedocs/gdb/Breakpoints-In-Python.html</a>)</p>
  
  <p>However when I try the following code I get the error "TypeError: Error when calling the metaclass bases. type 'gdb.Breakpoint' is not an acceptable base type"</p>
  
  <pre><code>class MyBreakpoint(gdb.Breakpoint):
    def stop (self):
      print "break"
      return False
  </code></pre>
  
  <p>I'm running Ubuntu 11.04 and gdb 7.2. Any help or links to better documentation would be appreciated. Thanks!</p>
  
  <p>My exact steps:</p>
  
  <pre><code>$ gdb
  GNU gdb (Ubuntu/Linaro 7.2-1ubuntu11) 7.2
  Copyright (C) 2010 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
  and "show warranty" for details.
  This GDB was configured as "i686-linux-gnu".
  For bug reporting instructions, please see:
  &lt;http://www.gnu.org/software/gdb/bugs/&gt;.
  (gdb) source t.py 
  Traceback (most recent call last):
    File "t.py", line 3, in &lt;module&gt;
      class MyBreakpoint(gdb.Breakpoint):
  TypeError: Error when calling the metaclass bases
      type 'gdb.Breakpoint' is not an acceptable base type
  (gdb) 
  </code></pre>