# 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
class FrequencyList(list):
def __init__(self, members):
super().__init__(members)
def frequency(self):
counts = {}
for item in self:
counts.setdefault(item, 0)
counts[item] += 1
return counts
# Example 2
foo = FrequencyList(['a', 'b', 'a', 'c', 'b', 'a', 'd'])
print('Length is', len(foo))
foo.pop()
print('After pop:', repr(foo))
print('Frequency:', foo.frequency())
Length is 7 After pop: ['a', 'b', 'a', 'c', 'b', 'a'] Frequency: {'c': 1, 'a': 3, 'b': 2}
# Example 3
class BinaryNode(object):
def __init__(self, value, left=None, right=None):
self.value = value
self.left = left
self.right = right
# Example 4
bar = [1, 2, 3]
bar[0]
1
# Example 5
bar.__getitem__(0)
1
# Example 6
class IndexableNode(BinaryNode):
def _search(self, count, index):
found = None
if self.left:
found, count = self.left._search(count, index)
if not found and count == index:
found = self
else:
count += 1
if not found and self.right:
found, count = self.right._search(count, index)
return found, count
# Returns (found, count)
def __getitem__(self, index):
found, _ = self._search(0, index)
if not found:
raise IndexError('Index out of range')
return found.value
# Example 7
tree = IndexableNode(
10,
left=IndexableNode(
5,
left=IndexableNode(2),
right=IndexableNode(
6, right=IndexableNode(7))),
right=IndexableNode(
15, left=IndexableNode(11)))
# Example 8
print('LRR =', tree.left.right.right.value)
print('Index 0 =', tree[0])
print('Index 1 =', tree[1])
print('11 in the tree?', 11 in tree)
print('17 in the tree?', 17 in tree)
print('Tree is', list(tree))
LRR = 7 Index 0 = 2 Index 1 = 5 11 in the tree? True 17 in the tree? False Tree is [2, 5, 6, 7, 10, 11, 15]
# Example 9
try:
len(tree)
except:
logging.exception('Expected')
else:
assert False
# Example 10
class SequenceNode(IndexableNode):
def __len__(self):
_, count = self._search(0, None)
return count
# Example 11
tree = SequenceNode(
10,
left=SequenceNode(
5,
left=SequenceNode(2),
right=SequenceNode(
6, right=SequenceNode(7))),
right=SequenceNode(
15, left=SequenceNode(11))
)
print('Tree has %d nodes' % len(tree))
Tree has 7 nodes
# Example 12
try:
from collections.abc import Sequence
class BadType(Sequence):
pass
foo = BadType()
except:
logging.exception('Expected')
else:
assert False
# Example 13
class BetterNode(SequenceNode, Sequence):
pass
tree = BetterNode(
10,
left=BetterNode(
5,
left=BetterNode(2),
right=BetterNode(
6, right=BetterNode(7))),
right=BetterNode(
15, left=BetterNode(11))
)
print('Index of 7 is', tree.index(7))
print('Count of 10 is', tree.count(10))
Index of 7 is 3 Count of 10 is 1