How to use the collections module for advanced data structure operations in Python 2.x

How to use the collections module for advanced data structure operations in Python 2.x

Introduction:
In the Python standard library, the collections module provides some advanced data structures, which can easily perform various operate. This article will introduce several data structures mainly provided by the collections module and give relevant code examples.

1. Counter
Counter is a simple and powerful counter tool that can be used to count the number of occurrences of each element in an iterable object.

Sample code:

from collections import Counter

# 统计一个列表中每个元素的出现次数
lst = [1, 1, 2, 3, 4, 4, 4, 5, 6, 6, 7]
counter = Counter(lst)
print(counter)

# 输出结果
# Counter({4: 3, 1: 2, 6: 2, 2: 1, 3: 1, 5: 1, 7: 1})

# 统计一个字符串中每个字符的出现次数
s = "Hello, World!"
counter = Counter(s)
print(counter)

# 输出结果
# Counter({'l': 3, 'o': 2, 'H': 1, 'e': 1, ',': 1, ' ': 1, 'W': 1, 'r': 1, 'd': 1, '!': 1})

# 获取出现次数最多的前3个元素及其次数
print(counter.most_common(3))

# 输出结果
# [('l', 3), ('o', 2), ('H', 1)]

2. defaultdict
defaultdict is a subclass of the built-in dictionary type. It overrides a method: __missing__(), which allows you to obtain an unknown When the value of the key is specified, a default value is returned.

Sample code:

from collections import defaultdict

# 声明一个defaultdict，键的默认值设为0
d = defaultdict(int)
print(d[1])

# 输出结果
# 0

# 声明一个defaultdict，键的默认值设为[]
d = defaultdict(list)
print(d[1])

# 输出结果
# []

# 声明一个defaultdict，键的默认值设为None
d = defaultdict(lambda: None)
print(d[1])

# 输出结果
# None

3. OrderedDict
OrderedDict is an ordered dictionary that remembers the order in which elements are inserted.

Sample code:

from collections import OrderedDict

# 声明一个OrderedDict
d = OrderedDict()

# 添加键值对
d[1] = 'a'
d[2] = 'b'
d[3] = 'c'

# 遍历字典
for k, v in d.items():
    print(k, v)

# 输出结果
# 1 a
# 2 b
# 3 c

4. deque
deque is a double-ended queue, which is thread-safe and can operate queues and stacks efficiently.

Sample code:

from collections import deque

# 创建一个双端队列
d = deque()

# 添加元素
d.append(1)
d.append(2)
d.append(3)

# 输出队列元素
print(d)

# 输出结果
# deque([1, 2, 3])

# 弹出元素
print(d.popleft())
print(d.pop())

# 输出结果
# 1
# 3

Summary:
This article introduces the basic usage of several advanced data structures provided by the collections module. Counter can conveniently count the number of occurrences of elements, defaultdict can set the default value of a key, OrderedDict can remember the insertion order of elements, and deque can efficiently perform queue and stack operations. In actual Python development, the flexible use of these data structures will bring a more efficient programming experience.

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