Which is a way of reminding you that I need to think as I write the code about what are my expectations from the input, and how might I enforce them.

通过这个我在提醒大家,在写代码的时候,要搞清楚对输入的期望，并思考下如何执行这些期望。

麻省理工公开课 - 计算机科学及编程导论课程节选

How do they manage to enforce those contracts?

他们怎么通过强制力约束合同的

耶鲁公开课 - 博弈论课程节选