Setting __module__ to None breaks pretty printing

[asmeurer]

In [1]: class Test: pass

In [2]: Test.__module__ = None

In [4]: Test
Out[4]: ---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-2205e48de5f9> in <module>()
----> 1 Test

/Users/aaronmeurer/Documents/ipython/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)

/Users/aaronmeurer/Documents/ipython/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):

/Users/aaronmeurer/Documents/ipython/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

/Users/aaronmeurer/Documents/ipython/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()

/Users/aaronmeurer/Documents/ipython/IPython/lib/pretty.pyc in pretty(self, obj)
    343                 if cls in self.type_pprinters:
    344                     # printer registered in self.type_pprinters
--> 345                     return self.type_pprinters[cls](obj, self, cycle)
    346                 else:
    347                     # deferred printer

/Users/aaronmeurer/Documents/ipython/IPython/lib/pretty.pyc in _type_pprint(obj, p, cycle)
    612         name = obj.__name__
    613     else:
--> 614         name = mod + '.' + obj.__name__
    615     p.text(name)
    616

TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

Setting __module__ to None is a way to make pickling work for dynamically defined classes in certain cases (see for example https://code.google.com/p/sympy/issues/detail?id=1198). The whichmodule function in the pickling module does a custom search for the module if __module__ is set to None.

[minrk]

try PR #3377