small refactoring

_pytest/assertrewrite.py

@@ -113,11 +113,16 @@ class AssertionRewriter(ast.NodeVisitor):
         for parent, pos, assert_ in asserts:
             parent[pos:pos + 1] = self.visit(assert_)
 
-    def assign(self, expr):
-        """Give *expr* a name."""
+    def variable(self):
+        """Get a new variable."""
         # Use a character invalid in python identifiers to avoid clashing.
         name = "@py_assert" + str(next(self.variable_counter))
         self.variables.add(name)
+        return name
+
+    def assign(self, expr):
+        """Give *expr* a name."""
+        name = self.variable()
         self.statements.append(ast.Assign([ast.Name(name, ast.Store())], expr))
         return ast.Name(name, ast.Load())
 
@@ -275,8 +280,7 @@ class AssertionRewriter(ast.NodeVisitor):
     def visit_Compare(self, comp):
         self.push_format_context()
         left_res, left_expl = self.visit(comp.left)
-        res_variables = ["@py_assert" + str(next(self.variable_counter))
-                         for i in range(len(comp.ops))]
+        res_variables = [self.variable() for i in range(len(comp.ops))]
         load_names = [ast.Name(v, ast.Load()) for v in res_variables]
         store_names = [ast.Name(v, ast.Store()) for v in res_variables]
         it = zip(range(len(comp.ops)), comp.ops, comp.comparators)