Use %{ %} instead of { } after %pythoncode

Simpler and safer change to address PR#357.

Lib/python/std_pair.i

@@ -176,7 +176,7 @@ SwigPython_std_pair_setitem (PyObject *a, Py_ssize_t b, PyObject *c)
 %define %swig_pair_methods(pair...)
 #if !defined(SWIGPYTHON_BUILTIN)
 %extend {      
-%pythoncode {def __len__(self):
+%pythoncode %{def __len__(self):
     return 2
 def __repr__(self):
     return str((self.first, self.second))
@@ -189,7 +189,7 @@ def __setitem__(self, index, val):
     if not (index % 2):
         self.first = val
     else:
-        self.second = val}
+        self.second = val%}
 }
 #endif
 %enddef