Closure and Decorators

Posted on 10/06/2019 in Python

Python Foundation

Local Functions Example 
store = []

def sort_by_last_letter(strings):
    def last_letter(s):
        return s[-1]
    store.append(last_letter)
    print(last_letter)
    return sorted(strings, key=last_letter)

sort_by_last_letter(['a','c','b'])
<function sort_by_last_letter.<locals>.last_letter at 0x102a149e0>
Out[5]: ['a', 'b', 'c']
sort_by_last_letter(['a','c','b'])
<function sort_by_last_letter.<locals>.last_letter at 0x102a14950>
Out[6]: ['a', 'b', 'c']
sort_by_last_letter(['a','c','b'])
<function sort_by_last_letter.<locals>.last_letter at 0x102a14b00>
Out[7]: ['a', 'b', 'c']
The main point here is that the def call in **sort_by_last_letter** is no different from any other name binding in the function, and a new function is created each time def is executed.

Remember the LEGB rule for name lookup. First the local scope is checked, then the enclosing scope, next the global scope, and finally the built-in scope.

  • useful for specialized, one-off functions
  • Aid in code organization and readability
  • Similar to lambdas, but more general
    • May contain multiple expressions
    • May contain statements