Initial patch as sent to py-dev

With a small but disasterous typo fixed though.

--HG--
branch : trunk

py/_code/_assertionnew.py

@@ -162,10 +162,7 @@ class DebugInterpreter(ast.NodeVisitor):
     def visit_Compare(self, comp):
         left = comp.left
         left_explanation, left_result = self.visit(left)
-        got_result = False
         for op, next_op in zip(comp.ops, comp.comparators):
-            if got_result and not result:
-                break
             next_explanation, next_result = self.visit(next_op)
             op_symbol = operator_map[op.__class__]
             explanation = "%s %s %s" % (left_explanation, op_symbol,
@@ -177,9 +174,16 @@ class DebugInterpreter(ast.NodeVisitor):
                                          __exprinfo_right=next_result)
             except Exception:
                 raise Failure(explanation)
-            else:
-                got_result = True
+            if not result:
+                break
             left_explanation, left_result = next_explanation, next_result
+        hook_result = py.test.config.hook.pytest_assert_compare(
+            op=op_symbol, left=left_result, right=next_result)
+        if hook_result:
+            for new_expl in hook_result:
+                if new_expl:
+                    explanation = '\n~'.join(new_expl)
+                    break
         return explanation, result
 
     def visit_BoolOp(self, boolop):

py/_code/assertion.py

@@ -5,12 +5,20 @@ BuiltinAssertionError = py.builtin.builtins.AssertionError
 
 
 def _format_explanation(explanation):
-    # uck!  See CallFunc for where \n{ and \n} escape sequences are used
+    """This formats an explanation
+
+    Normally all embedded newlines are escaped, however there are
+    three exceptions: \n{, \n} and \n~.  The first two are intended
+    cover nested explanations, see function and attribute explanations
+    for examples (.visit_Call(), visit_Attribute()).  The last one is
+    for when one explanation needs to span multiple lines, e.g. when
+    displaying diffs.
+    """
     raw_lines = (explanation or '').split('\n')
-    # escape newlines not followed by { and }
+    # escape newlines not followed by {, } and ~
     lines = [raw_lines[0]]
     for l in raw_lines[1:]:
-        if l.startswith('{') or l.startswith('}'):
+        if l.startswith('{') or l.startswith('}') or l.startswith('~'):
             lines.append(l)
         else:
             lines[-1] += '\\n' + l
@@ -28,11 +36,14 @@ def _format_explanation(explanation):
             stackcnt[-1] += 1
             stackcnt.append(0)
             result.append(' +' + '  '*(len(stack)-1) + s + line[1:])
-        else:
+        elif line.startswith('}'):
             assert line.startswith('}')
             stack.pop()
             stackcnt.pop()
             result[stack[-1]] += line[1:]
+        else:
+            assert line.startswith('~')
+            result.append('  '*len(stack) + line[1:])
     assert len(stack) == 1
     return '\n'.join(result)
 

py/_plugin/hookspec.py

@@ -123,6 +123,19 @@ def pytest_sessionstart(session):
 def pytest_sessionfinish(session, exitstatus):
     """ whole test run finishes. """
 
+# -------------------------------------------------------------------------
+# hooks for customising the assert methods
+# -------------------------------------------------------------------------
+
+def pytest_assert_compare(op, left, right):
+    """Customise compare assertion
+
+    Return None or an empty list for no custom compare, otherwise
+    return a list of strings.  The strings will be joined by newlines
+    but any newlines *in* as string will be escaped.  Note that all
+    but the first line will be indented sligthly.
+    """
+
 # -------------------------------------------------------------------------
 # hooks for influencing reporting (invoked from pytest_terminal)
 # -------------------------------------------------------------------------

py/_plugin/pytest_assertion.py

@@ -1,3 +1,6 @@
+import difflib
+import pprint
+
 import py
 import sys
 
@@ -26,3 +29,49 @@ def warn_about_missing_assertion():
     else:
         py.std.warnings.warn("Assertions are turned off!"
                              " (are you using python -O?)")
+
+
+def pytest_assert_compare(op, left, right):
+    """Make a specialised explanation for comapare equal"""
+    if op != '==' or type(left) != type(right):
+        return None
+    explanation = []
+    left_repr = py.io.saferepr(left, maxsize=30)
+    right_repr = py.io.saferepr(right, maxsize=30)
+    explanation += ['%s == %s' % (left_repr, right_repr)]
+    issquence = lambda x: isinstance(x, (list, tuple))
+    istext = lambda x: isinstance(x, basestring)
+    isdict = lambda x: isinstance(x, dict)
+    if istext(left):
+        explanation += [line.strip('\n') for line in
+                        difflib.ndiff(left.splitlines(), right.splitlines())]
+    elif issquence(left):
+        explanation += _compare_eq_sequence(left, right)
+    elif isdict(left):
+        explanation += _pprint_diff(left, right)
+    else:
+        return None         # No specialised knowledge
+    return explanation
+
+
+def _compare_eq_sequence(left, right):
+    explanation = []
+    for i in xrange(min(len(left), len(right))):
+        if left[i] != right[i]:
+            explanation += ['First differing item %s: %s != %s' %
+                            (i, left[i], right[i])]
+            break
+    if len(left) > len(right):
+        explanation += ['Left contains more items, '
+                        'first extra item: %s' % left[len(right)]]
+    elif len(left) < len(right):
+        explanation += ['Right contains more items, '
+                        'first extra item: %s' % right[len(right)]]
+    return explanation + _pprint_diff(left, right)
+
+
+def _pprint_diff(left, right):
+    """Make explanation using pprint and difflib"""
+    return [line.strip('\n') for line in
+            difflib.ndiff(pprint.pformat(left).splitlines(),
+                          pprint.pformat(right).splitlines())]