A reduced example that I'm currently using:

class DebugPrintingBreakpoint(gdb.Breakpoint):
    debugging_IDs = frozenset({37, 153, 420})
    def stop(self):
        top = gdb.newest_frame()
        someVector = top.read_var('aVectorVar')
        # Access the begin() & end() pointer of std::vector in GNU Standard C++ lib
        first = someVector['_M_impl']['_M_start']
        last = someVector['_M_impl']['_M_finish']
        values = []
        while first != last:
            values.append(int(first.dereference()['intID']))
            first = first + 1
        if not set(values) & debugging_IDs:
            return False # skip: none of the items we're looking for can be found by ID in the vector on the stack
        print("Found other accompanying IDs: {}".format(values))
        return True # drop to gdb's prompt
# Ensure shared libraries are loaded already
gdb.execute("start")
# Set our breakpoint, which happens to reside in some shared lib, hence the "start" previously
DebugPrintingBreakpoint("source.cpp:42")
gdb.execute("continue")

You can execute this script from gdb's prompt like this:

(gdb) source script.py

Or from the command-line:

$ gdb --command script.py ./executable.elf

See the complete GDB Python API docs for further info.