Bugfix: Fix cpp iteration over attribute of temporary object

Cython/Compiler/ExprNodes.py

@@ -293,6 +293,23 @@ def translate_double_cpp_exception(code, pos, lhs_type, lhs_code, rhs_code, lhs_
     code.putln(code.error_goto(pos))
     code.putln('}')
 
+# Used to determine if a node has a persistent result, meaning it is not temporary
+# and doesn't depend on any temporary sub expressions.
+# Examples:
+#       name                # <- persistent
+#       name.attr           # <- persistent
+#       some_func()         # <- temporary
+#       some_func().attr    # <- temporary
+# Essentially this boils down to NameNodes and AttributeNodes that are recursively
+# only composed of NameNodes.
+def is_persistent(node):
+    if node.is_name:
+        return True
+    elif node.is_attribute:
+        return is_persistent(node.obj)
+    else:
+        return False
+
 
 class ExprNode(Node):
     #  subexprs     [string]     Class var holding names of subexpr node attrs
@@ -2920,7 +2937,7 @@ class CppIteratorNode(ExprNode):
         if sequence_type.is_cyp_class:
             self.cpp_attribute_op = "->"
         # essentially 3 options:
-        if self.sequence.is_name or self.sequence.is_attribute:
+        if is_persistent(self.sequence):
             # 1) is a name and can be accessed directly;
             #    assigning to it may break the container, but that's the responsibility
             #    of the user