code: def assign(self, var, val, assignment):
          "Add {var: val} to assignment; Discard the old value if any."
          assignment[var] = val
          self.nassigns += f assign(self, var, val, assignment):
          "Add {var: val} to assignment; Discard the old value if any."
          assignment[var] = val
          self.nassigns += 1
docs: Add {var: val} to assignment; Discard the old value if any.