rewrote the initpkg mechanism and moved py lib implementation files to

_py/...  with py/__init__.py containing pointers into them

The new apipkg is only around 70 lines of code and allows
us to get rid of the infamous "py.__." by regular non-magical
"_py." imports. It is also available as a separately installable
package, see http://bitbucket.org/hpk42/apipkg

--HG--
branch : trunk

_py/code/assertion.py

@@ -0,0 +1,75 @@
+import sys
+import py
+
+BuiltinAssertionError = py.builtin.builtins.AssertionError
+
+
+def _format_explanation(explanation):
+    # uck!  See CallFunc for where \n{ and \n} escape sequences are used
+    raw_lines = (explanation or '').split('\n')
+    # escape newlines not followed by { and }
+    lines = [raw_lines[0]]
+    for l in raw_lines[1:]:
+        if l.startswith('{') or l.startswith('}'):
+            lines.append(l)
+        else:
+            lines[-1] += '\\n' + l
+
+    result = lines[:1]
+    stack = [0]
+    stackcnt = [0]
+    for line in lines[1:]:
+        if line.startswith('{'):
+            if stackcnt[-1]:
+                s = 'and   '
+            else:
+                s = 'where '
+            stack.append(len(result))
+            stackcnt[-1] += 1
+            stackcnt.append(0)
+            result.append(' +' + '  '*(len(stack)-1) + s + line[1:])
+        else:
+            assert line.startswith('}')
+            stack.pop()
+            stackcnt.pop()
+            result[stack[-1]] += line[1:]
+    assert len(stack) == 1
+    return '\n'.join(result)
+
+
+if sys.version_info >= (2, 6):
+    from _py.code._assertionnew import interpret
+else:
+    from _py.code._assertionold import interpret
+
+
+class AssertionError(BuiltinAssertionError):
+
+    def __init__(self, *args):
+        BuiltinAssertionError.__init__(self, *args)
+        if args:
+            try:
+                self.msg = str(args[0])
+            except (KeyboardInterrupt, SystemExit):
+                raise
+            except:
+                self.msg = "<[broken __repr__] %s at %0xd>" %(
+                    args[0].__class__, id(args[0]))
+        else:
+            f = py.code.Frame(sys._getframe(1))
+            try:
+                source = f.statement
+                source = str(source.deindent()).strip()
+            except py.error.ENOENT:
+                source = None
+                # this can also occur during reinterpretation, when the
+                # co_filename is set to "<run>".
+            if source:
+                self.msg = interpret(source, f, should_fail=True)
+                if not self.args:
+                    self.args = (self.msg,)
+            else:
+                self.msg = None
+
+if sys.version_info > (3, 0):
+    AssertionError.__module__ = "builtins"