another pass on formatter lookup

- pop takes a default value (like dict)
- support `type in Formatter`
- allow lookup by type string (for consistency)

IPython/core/formatters.py

@@ -208,7 +208,10 b' class FormatterABC(with_metaclass(abc.ABCMeta, object)):'
 
 
 def _mod_name_key(typ):
-    """Return a '__module__.__name__' string key for a type."""
+    """Return a (__module__, __name__) tuple for a type.
+    
+    Used as key in Formatter.deferred_printers.
+    """
     module = getattr(typ, '__module__', None)
     name = getattr(typ, '__name__', None)
     return (module, name)
@@ -218,6 +221,7 b' def _get_type(obj):'
     """Return the type of an instance (old and new-style)"""
     return getattr(obj, '__class__', None) or type(obj)
 
+_raise_key_error = object()
 
 class BaseFormatter(Configurable):
     """A base formatter class that is configurable.
@@ -283,6 +287,15 b' class BaseFormatter(Configurable):'
         else:
             return None
     
+    def __contains__(self, typ):
+        """map in to lookup_by_type"""
+        try:
+            self.lookup_by_type(typ)
+        except KeyError:
+            return False
+        else:
+            return True
+    
     def lookup(self, obj):
         """Look up the formatter for a given instance.
         
@@ -293,7 +306,7 b' class BaseFormatter(Configurable):'
         Returns
         -------
         f : callable
-            The registered fromatting callable for the type.
+            The registered formatting callable for the type.
 
         Raises
         ------
@@ -307,7 +320,7 b' class BaseFormatter(Configurable):'
         return self.lookup_by_type(_get_type(obj))
     
     def lookup_by_type(self, typ):
-        """ Look up all the registered formatters for a type.
+        """Look up the registered formatter for a type.
 
         Parameters
         ----------
@@ -316,15 +329,26 b' class BaseFormatter(Configurable):'
         Returns
         -------
         f : callable
-            The registered fromatting callable for the type.
+            The registered formatting callable for the type.
 
         Raises
         ------
         KeyError if the type has not been registered.
         """
-        for cls in pretty._get_mro(typ):
-            if cls in self.type_printers or self._in_deferred_types(cls):
-                return self.type_printers[cls]
+        if isinstance(typ, string_types):
+            typ_key = tuple(typ.rsplit('.',1))
+            if typ_key not in self.deferred_printers:
+                # We may have it cached in the type map. We will have to
+                # iterate over all of the types to check.
+                for cls in self.type_printers:
+                    if _mod_name_key(cls) == typ_key:
+                        return self.type_printers[cls]
+            else:
+                return self.deferred_printers[typ_key]
+        else:
+            for cls in pretty._get_mro(typ):
+                if cls in self.type_printers or self._in_deferred_types(cls):
+                    return self.type_printers[cls]
         
         # If we have reached here, the lookup failed.
         raise KeyError("No registered printer for {0!r}".format(typ))
@@ -398,17 +422,23 b' class BaseFormatter(Configurable):'
         """
         key = (type_module, type_name)
         
-        oldfunc = self.deferred_printers.get(key, None)
+        try:
+            oldfunc = self.lookup_by_type("%s.%s" % key)
+        except KeyError:
+            oldfunc = None
+        
         if func is not None:
             self.deferred_printers[key] = func
         return oldfunc
     
-    def pop(self, typ):
-        """ Pop a registered object for the given type.
+    def pop(self, typ, default=_raise_key_error):
+        """Pop a formatter for the given type.
 
         Parameters
         ----------
         typ : type or '__module__.__name__' string for a type
+        default : object
+            value to be returned if no formatter is registered for typ.
 
         Returns
         -------
@@ -417,8 +447,9 b' class BaseFormatter(Configurable):'
 
         Raises
         ------
-        KeyError if the type is not registered.
+        KeyError if the type is not registered and default is not specified.
         """
+        
         if isinstance(typ, string_types):
             typ_key = tuple(typ.rsplit('.',1))
             if typ_key not in self.deferred_printers:
@@ -429,14 +460,16 b' class BaseFormatter(Configurable):'
                         old = self.type_printers.pop(cls)
                         break
                 else:
-                    raise KeyError("No registered value for {0!r}".format(typ_key))
+                    old = default
             else:
                 old = self.deferred_printers.pop(typ_key)
         else:
             if typ in self.type_printers:
                 old = self.type_printers.pop(typ)
             else:
-                old = self.deferred_printers.pop(_mod_name_key(typ))
+                old = self.deferred_printers.pop(_mod_name_key(typ), default)
+        if old is _raise_key_error:
+            raise KeyError("No registered value for {0!r}".format(typ))
         return old
 
     def _in_deferred_types(self, cls):

IPython/core/pylabtools.py

@@ -173,22 +173,13 b' def select_figure_format(shell, fmt):'
     png_formatter = shell.display_formatter.formatters['image/png']
 
     if fmt == 'png':
-        try:
-            svg_formatter.pop(Figure)
-        except KeyError:
-            pass
+        svg_formatter.pop(Figure, None)
         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png'))
     elif fmt in ('png2x', 'retina'):
-        try:
-            svg_formatter.pop(Figure)
-        except KeyError:
-            pass
+        svg_formatter.pop(Figure, None)
         png_formatter.for_type(Figure, retina_figure)
     elif fmt == 'svg':
-        try:
-            svg_formatter.pop(Figure)
-        except KeyError:
-            pass
+        png_formatter.pop(Figure, None)
         svg_formatter.for_type(Figure, lambda fig: print_figure(fig, 'svg'))
     else:
         raise ValueError("supported formats are: 'png', 'retina', 'svg', not %r" % fmt)

IPython/core/tests/test_formatters.py

@@ -169,22 +169,44 b' def test_lookup_by_type_string():'
     nt.assert_in(_mod_name_key(C), f.deferred_printers)
     nt.assert_not_in(C, f.type_printers)
     
+    nt.assert_is(f.lookup_by_type(type_str), foo_printer)
+    # lookup by string doesn't cause import
+    nt.assert_in(_mod_name_key(C), f.deferred_printers)
+    nt.assert_not_in(C, f.type_printers)
+    
     nt.assert_is(f.lookup_by_type(C), foo_printer)
     # should move from deferred to imported dict
     nt.assert_not_in(_mod_name_key(C), f.deferred_printers)
     nt.assert_in(C, f.type_printers)
 
+def test_in_formatter():
+    f = PlainTextFormatter()
+    f.for_type(C, foo_printer)
+    type_str = '%s.%s' % (C.__module__, 'C')
+    nt.assert_in(C, f)
+    nt.assert_in(type_str, f)
+
+def test_string_in_formatter():
+    f = PlainTextFormatter()
+    type_str = '%s.%s' % (C.__module__, 'C')
+    f.for_type(type_str, foo_printer)
+    nt.assert_in(type_str, f)
+    nt.assert_in(C, f)
+
 def test_pop():
     f = PlainTextFormatter()
     f.for_type(C, foo_printer)
     nt.assert_is(f.lookup_by_type(C), foo_printer)
-    f.pop(C)
+    nt.assert_is(f.pop(C, None), foo_printer)
+    f.for_type(C, foo_printer)
+    nt.assert_is(f.pop(C), foo_printer)
     with nt.assert_raises(KeyError):
         f.lookup_by_type(C)
     with nt.assert_raises(KeyError):
         f.pop(C)
     with nt.assert_raises(KeyError):
         f.pop(A)
+    nt.assert_is(f.pop(A, None), None)
 
 def test_pop_string():
     f = PlainTextFormatter()
@@ -201,10 +223,12 b' def test_pop_string():'
         f.pop(type_str)
 
     f.for_type(C, foo_printer)
-    f.pop(type_str)
+    nt.assert_is(f.pop(type_str, None), foo_printer)
     with nt.assert_raises(KeyError):
         f.lookup_by_type(C)
     with nt.assert_raises(KeyError):
         f.pop(type_str)
+    nt.assert_is(f.pop(type_str, None), None)
+