I realize that my argument about arbitrary constants was not making much sense. But what I meant to convey was that it will be hard to write and maintain code if we allow Python Lambda.

So, this docstring might be a good place to introduce new users to `Sympy.Lambda`, giving Python lambda in examples might leave an impression that Python lambda's are the right thing to use.
I take your suggestion of supporting novice users, but I think we should discourage them from using Python lambda. Adding a note in tutorials might help us do that.