Add a function to compute a class's method resolution order. This is

easy for 2.2 new-style classes, but trickier for classic classes, and
different approaches are needed "depending".  The function will allow
later code to treat all flavors of classes uniformly.

2 files changed, 38 insertions, 0 deletions

diff --git a/Lib/inspect.py b/Lib/inspect.py
index 1102c3b..3febf18 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -163,6 +163,24 @@ def getmembers(object, predicate=None):
     results.sort()
     return results
 
+# ----------------------------------------------------------- class helpers
+def _searchbases(cls, accum):
+    # Simulate the "classic class" search order.
+    if cls in accum:
+        return
+    accum.append(cls)
+    for base in cls.__bases__:
+        _searchbases(base, accum)
+
+def getmro(cls):
+    "Return tuple of base classes (including cls) in method resolution order."
+    if hasattr(cls, "__mro__"):
+        return cls.__mro__
+    else:
+        result = []
+        _searchbases(cls, result)
+        return tuple(result)
+
 # -------------------------------------------------- source code extraction
 def indentsize(line):
     """Return the indent size, in spaces, at the start of a line of text."""
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index 130fa8e..dbb6609 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -213,3 +213,23 @@ for fname in files_to_clean_up:
         os.unlink(fname)
     except:
         pass
+
+# Test classic-class method resolution order.
+class A:    pass
+class B(A): pass
+class C(A): pass
+class D(B, C): pass
+
+expected = (D, B, A, C)
+got = inspect.getmro(D)
+test(expected == got, "expected %r mro, got %r", expected, got)
+
+# The same w/ new-class MRO.
+class A(object):    pass
+class B(A): pass
+class C(A): pass
+class D(B, C): pass
+
+expected = (D, B, C, A, object)
+got = inspect.getmro(D)
+test(expected == got, "expected %r mro, got %r", expected, got)