I have tried to declare a convenience function as described in the documentation [1] but I am unable to call the new function afterwards. This has been tried using GDB 7.5 on Gentoo GNU/Linux as well as GDB 7.5 on MacOS X (installed via Homebrew) with the same result.

Here is the result when running the example from the documentation:

    (gdb) python
    >import gdb
    >class Greet(gdb.Function):
    >    def __init__(self):
    >        super(Greet, self).__init__('greet')
    >
    >    def invoke(self, name):
    >        return 'Hello %s' % name.string()
    >
    >Greet ()
    >end
    (gdb) greet test
    Undefined command: "greet".  Try "help".
    (gdb) greet
    Undefined command: "greet".  Try "help".

gdb.Command and gdb.Parameter both work as expected in the two GDB installations that I tried gdb.Function in.

GDB 7.5 on OSX:
    $ uname -a
    Darwin moonglow.local 12.2.0 Darwin Kernel Version 12.2.0: Sat Aug 25 00:48:52 PDT 2012; root:xnu-2050.18.24~1/RELEASE_X86_64 x86_64

    $ gcc -v
    Using built-in specs.
    Target: i686-apple-darwin11
    Configured with: /private/var/tmp/llvmgcc42/llvmgcc42-2336.11~67/src/configure --disable-checking --enable-werror --prefix=/Applications/Xcode.app/Contents/Developer/usr/llvm-gcc-4.2 --mandir=/share/man --enable-languages=c,objc,c++,obj-c++ --program-prefix=llvm- --program-transform-name=/^[cg][^.-]*$/s/$/-4.2/ --with-slibdir=/usr/lib --build=i686-apple-darwin11 --enable-llvm=/private/var/tmp/llvmgcc42/llvmgcc42-2336.11~67/dst-llvmCore/Developer/usr/local --program-prefix=i686-apple-darwin11- --host=x86_64-apple-darwin11 --target=i686-apple-darwin11 --with-gxx-include-dir=/usr/include/c++/4.2.1
    Thread model: posix
    gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)

    $ gdb
    GNU gdb (GDB) 7.5
    [..]
    This GDB was configured as "x86_64-apple-darwin12.1.0".


GDB 7.5 on Gentoo:
    $ uname -a
    Linux moonglow-gentoo 3.5.2-gentoo #3 SMP PREEMPT Sat Aug 25 07:32:50 CEST 2012 x86_64 Intel(R) Core(TM) i7-2720QM CPU @ 2.20GHz GenuineIntel GNU/Linux

    $ gcc -v
    Using built-in specs.
    COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.3/gcc
    COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.6.3/lto-wrapper
    Target: x86_64-pc-linux-gnu
    Configured with: /var/tmp/portage/sys-devel/gcc-4.6.3/work/gcc-4.6.3/configure --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.3 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.3 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.3/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.3/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include/g++-v4 --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec --disable-fixed-point --with-ppl --with-cloog --disable-ppl-version-check --with-cloog-include=/usr/include/cloog-ppl --enable-lto --disable-nls --with-system-zlib --enable-obsolete --disable-werror --enable-secureplt --enable-multilib --enable-libmudflap --disable-libssp --enable-libgomp --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.6.3/python --enable-checking=release --disable-libgcj --enable-languages=c,c++,fortran --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-targets=all --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.6.3 p1.6, pie-0.5.2'
    Thread model: posix
    gcc version 4.6.3 (Gentoo 4.6.3 p1.6, pie-0.5.2) 

    $ gdb
    GNU gdb (Gentoo 7.5 p1) 7.5
    [..]
    This GDB was configured as "x86_64-pc-linux-gnu".


 [1] http://sourceware.org/gdb/current/onlinedocs/gdb/Functions-In-Python.html#Functions-In-Python