#!/usr/bin/env python3 # Copyright 2014 Brett Slatkin, Pearson Education Inc. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. # Preamble to mimick book environment import logging from pprint import pprint from sys import stdout as STDOUT # Example 1 names = ['Socrates', 'Archimedes', 'Plato', 'Aristotle'] names.sort(key=lambda x: len(x)) print(names) # Example 2 from collections import defaultdict def log_missing(): print('Key added') return 0 # Example 3 current = {'green': 12, 'blue': 3} increments = [ ('red', 5), ('blue', 17), ('orange', 9), ] result = defaultdict(log_missing, current) print('Before:', dict(result)) for key, amount in increments: result[key] += amount print('After: ', dict(result)) # Example 4 def increment_with_report(current, increments): added_count = 0 def missing(): nonlocal added_count # Stateful closure added_count += 1 return 0 result = defaultdict(missing, current) for key, amount in increments: result[key] += amount return result, added_count # Example 5 result, count = increment_with_report(current, increments) assert count == 2 print(result) # Example 6 class CountMissing(object): def __init__(self): self.added = 0 def missing(self): self.added += 1 return 0 # Example 7 counter = CountMissing() result = defaultdict(counter.missing, current) # Method reference for key, amount in increments: result[key] += amount assert counter.added == 2 print(result) # Example 8 class BetterCountMissing(object): def __init__(self): self.added = 0 def __call__(self): self.added += 1 return 0 counter = BetterCountMissing() counter() assert callable(counter) # Example 9 counter = BetterCountMissing() result = defaultdict(counter, current) # Relies on __call__ for key, amount in increments: result[key] += amount assert counter.added == 2 print(result)