Functions are first-class objects
Python functions can be assigned to variables, stored in collections, passed as arguments and returned from other functions. This enables callback and higher-order programming patterns.
Where lambda fits
A lambda is a small anonymous function containing a single expression. It is convenient for short callbacks such as the key function passed to sorted(). For reusable or complicated logic, a named function is clearer.
Separate algorithm from policy
Functions such as sorted() can perform the algorithm while your callback defines the business-specific comparison or extraction rule. This is a powerful and reusable design pattern.
Practice: sort employee records by department and name, first with a lambda and then with a named key function.
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