ENH: Refactor pretty to allow it to run without global type registries.

IPython/external/pretty.py

@@ -306,10 +306,21 b' class RepresentationPrinter(PrettyPrinter):'
     verbose mode.
     """
 
-    def __init__(self, output, verbose=False, max_width=79, newline='\n'):
+    def __init__(self, output, verbose=False, max_width=79, newline='\n',
+        singleton_pprinters=None, type_pprinters=None, deferred_pprinters=None):
+
         PrettyPrinter.__init__(self, output, max_width, newline)
         self.verbose = verbose
         self.stack = []
+        if singleton_pprinters is None:
+            singleton_pprinters = _singleton_pprinters.copy()
+        self.singleton_pprinters = singleton_pprinters
+        if type_pprinters is None:
+            type_pprinters = _type_pprinters.copy()
+        self.type_pprinters = type_pprinters
+        if deferred_pprinters is None:
+            deferred_pprinters = _deferred_type_pprinters.copy()
+        self.deferred_pprinters = deferred_pprinters
 
     def pretty(self, obj):
         """Pretty print the given object."""
@@ -322,14 +333,14 b' class RepresentationPrinter(PrettyPrinter):'
             if hasattr(obj_class, '__pretty__'):
                 return obj_class.__pretty__(obj, self, cycle)
             try:
-                printer = _singleton_pprinters[obj_id]
+                printer = self.singleton_pprinters[obj_id]
             except (TypeError, KeyError):
                 pass
             else:
                 return printer(obj, self, cycle)
             for cls in _get_mro(obj_class):
-                if cls in _type_pprinters:
-                    return _type_pprinters[cls](obj, self, cycle)
+                if cls in self.type_pprinters:
+                    return self.type_pprinters[cls](obj, self, cycle)
                 else:
                     printer = self._in_deferred_types(cls)
                     if printer is not None:
@@ -351,14 +362,13 b' class RepresentationPrinter(PrettyPrinter):'
         name = getattr(cls, '__name__', None)
         key = (mod, name)
         printer = None
-        if key in _deferred_type_pprinters:
+        if key in self.deferred_pprinters:
             # Move the printer over to the regular registry.
-            printer = _deferred_type_pprinters.pop(key)
-            _type_pprinters[cls] = printer
+            printer = self.deferred_pprinters.pop(key)
+            self.type_pprinters[cls] = printer
         return printer
 
 
-
 class Printable(object):
 
     def output(self, stream, output_width):