template.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/

An example of the Template pattern in Python

*TL;DR80
Defines the skeleton of an algorithm, deferring steps to subclasses.
"""

ingredients = "spam eggs apple"
line = '-' * 10


# Skeletons
def iter_elements(getter, action):
    """Template skeleton that iterates items"""
    for element in getter():
        action(element)
        print(line)


def rev_elements(getter, action):
    """Template skeleton that iterates items in reverse order"""
    for element in getter()[::-1]:
        action(element)
        print(line)


# Getters
def get_list():
    return ingredients.split()


def get_lists():
    return [list(x) for x in ingredients.split()]


# Actions
def print_item(item):
    print(item)


def reverse_item(item):
    print(item[::-1])


# Makes templates
def make_template(skeleton, getter, action):
    """Instantiate a template method with getter and action"""
    def template():
        skeleton(getter, action)
    return template

# Create our template functions
templates = [make_template(s, g, a)
             for g in (get_list, get_lists)
             for a in (print_item, reverse_item)
             for s in (iter_elements, rev_elements)]

# Execute them
for template in templates:
    template()

### OUTPUT ###
# spam
# ----------
# eggs
# ----------
# apple
# ----------
# apple
# ----------
# eggs
# ----------
# spam
# ----------
# maps
# ----------
# sgge
# ----------
# elppa
# ----------
# elppa
# ----------
# sgge
# ----------
# maps
# ----------
# ['s', 'p', 'a', 'm']
# ----------
# ['e', 'g', 'g', 's']
# ----------
# ['a', 'p', 'p', 'l', 'e']
# ----------
# ['a', 'p', 'p', 'l', 'e']
# ----------
# ['e', 'g', 'g', 's']
# ----------
# ['s', 'p', 'a', 'm']
# ----------
# ['m', 'a', 'p', 's']
# ----------
# ['s', 'g', 'g', 'e']
# ----------
# ['e', 'l', 'p', 'p', 'a']
# ----------
# ['e', 'l', 'p', 'p', 'a']
# ----------
# ['s', 'g', 'g', 'e']
# ----------
# ['m', 'a', 'p', 's']
# ----------