Twisted is a massive codebase, and uses zope.interface. There are definitely options for stricter guarantees, but it's optional, and generally you'd rather be t

Twisted is a massive codebase, and uses zope.interface. There are definitely options for stricter guarantees, but it's optional, and generally you'd rather be treating input as ducks. Also, even without actual type checking (mypy), IDE support + type hinting (PEP 484 or reST et al) means you can find most issues before the interpreter/compiler is involved. PyCharm is fantastic at this.