# 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)
['Plato', 'Socrates', 'Aristotle', 'Archimedes']
# 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))
Before: {'green': 12, 'blue': 3} Key added Key added After: {'red': 5, 'orange': 9, 'green': 12, 'blue': 20}
# 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)
defaultdict(<function increment_with_report.<locals>.missing at 0x103e7dd08>, {'red': 5, 'orange': 9, 'green': 12, 'blue': 20})
# 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)
defaultdict(<bound method CountMissing.missing of <__main__.CountMissing object at 0x103e8c550>>, {'red': 5, 'orange': 9, 'green': 12, 'blue': 20})
# 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)
defaultdict(<__main__.BetterCountMissing object at 0x103e8ca58>, {'red': 5, 'orange': 9, 'green': 12, 'blue': 20})