Matroid Union, ticket 14667

sage: M1=matroids.named_matroids.Fano()
sage: M2=matroids.named_matroids.Vamos()
sage: from sage.matroids.matroid_union import *
sage: MatroidUnion(M1,M2)
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
<ipython-input-4-07339b303c89> in <module>()
----> 1 MatroidUnion(M1,M2)

/home/rajesh/sage/local/lib/python2.7/site-packages/IPython/core/displayhook.pyc in __call__(self, result)
    236             self.start_displayhook()
    237             self.write_output_prompt()
--> 238             format_dict = self.compute_format_data(result)
    239             self.write_format_data(format_dict)
    240             self.update_user_ns(result)

/home/rajesh/sage/local/lib/python2.7/site-packages/IPython/core/displayhook.pyc in compute_format_data(self, result)
    148             MIME type representation of the object.
    149         """
--> 150         return self.shell.display_formatter.format(result)
    151
    152     def write_format_data(self, format_dict):

/home/rajesh/sage/local/lib/python2.7/site-packages/IPython/core/formatters.pyc in format(self, obj, include, exclude)
    124                     continue
    125             try:
--> 126                 data = formatter(obj)
    127             except:
    128                 # FIXME: log the exception

/home/rajesh/sage/local/lib/python2.7/site-packages/sage/misc/displayhook.pyc in __call__(self, obj)
    508         s = self.try_format_obj(obj)
    509         if s is None:
--> 510             s = super(SagePlainTextFormatter, self).__call__(obj)
    511         return s
    512

/home/rajesh/sage/local/lib/python2.7/site-packages/IPython/core/formatters.pyc in __call__(self, obj)
    445                 type_pprinters=self.type_printers,
    446                 deferred_pprinters=self.deferred_printers)
--> 447             printer.pretty(obj)
    448             printer.flush()
    449             return stream.getvalue()

/home/rajesh/sage/local/lib/python2.7/site-packages/IPython/lib/pretty.pyc in pretty(self, obj)
    358                             if callable(meth):
    359                                 return meth(obj, self, cycle)
--> 360             return _default_pprint(obj, self, cycle)
    361         finally:
    362             self.end_group()

/home/rajesh/sage/local/lib/python2.7/site-packages/IPython/lib/pretty.pyc in _default_pprint(obj, p, cycle)
    478     if getattr(klass, '__repr__', None) not in _baseclass_reprs:
    479         # A user-provided repr.
--> 480         p.text(repr(obj))
    481         return
    482     p.begin_group(1, '<')

/home/rajesh/sage/local/lib/python2.7/site-packages/sage/structure/sage_object.so in sage.structure.sage_object.SageObject.__repr__ (sage/structure/sage_object.c:1921)()

/home/rajesh/sage/local/lib/python2.7/site-packages/sage/matroids/matroid.so in sage.matroids.matroid.Matroid._repr_ (sage/matroids/matroid.c:7660)()

/home/rajesh/sage/local/lib/python2.7/site-packages/sage/matroids/matroid.so in sage.matroids.matroid.Matroid.rank (sage/matroids/matroid.c:7990)()

/home/rajesh/sage/local/lib/python2.7/site-packages/sage/matroids/matroid.so in sage.matroids.matroid.Matroid.full_rank (sage/matroids/matroid.c:8229)()

/home/rajesh/sage/local/lib/python2.7/site-packages/sage/matroids/matroid.so in sage.matroids.matroid.Matroid.groundset (sage/matroids/matroid.c:2089)()

NotImplementedError: subclasses need to implement this.