python 容器字典(Dictionaries)简介。

1、字典容器用于存储（key,value）对，是对哈希表的实现，访问时间复杂度为o(1).

简单用法如下：

d = {'cat': 'cute', 'dog': 'furry'}  # Create a new dictionary with some data

print(d['cat'])       # Get an entry from a dictionary; prints "cute"

print('cat' in d)     # Check if a dictionary has a given key; prints "争欧True"

d['fish'] = 'wet'     # Set an entry in a dictionary

print(d['fish'])      # Prints "wet"

# print(d['monkey'])  # KeyError: 'monkey' not a key of d

print(d.get('monkey', 'N/A'))  # Get an element with a default; prints "N/A"

print(d.get('fish', 'N/A'))    # Get an element with a default; prints "wet"

del d['fish']         # Remove an element from a dictionary

print(d.get('fish', 'N/A')) # "fish" is no longer a key; prints "N/A"

2、上述代码运行结果：

cute

True

wet

N/A

wet

N/A

3、循环：遍历字典中的key非常简单。

实现如下：

d = {'person': 2, 'cat': 4, 'spider': 8}

for animal in d:

    legs = d[animal]

    print('A %s has %d legs' % (animal, legs))

# Prints "A person has 2 legs", "A cat has 4 legs", "A spider has 8 legs"

4、结果如下：

A person has 2 legs

A cat has 4 legs

A spider has 8 legs

5、如果你低匠想同时获取字典的key和相应召喝压的value的话，可以使用items方法。

举个例子:

d = {'person': 2, 'cat': 4, 'spider': 8}

for animal, legs in d.items():

    print('A %s has %d legs' % (animal, legs))

# Prints "A person has 2 legs", "A cat has 4 legs", "A spider has 8 legs"

6、结果如下：

A person has 2 legs

A cat has 4 legs

A spider has 8 legs

7、可以简单的通过列表构建字典。

举个例子：

nums = [0, 1, 2, 3, 4]

even_num_to_square = {x: x ** 2 for x in nums if x % 2 == 0}

print(even_num_to_square)  # Prints "{0: 0, 2: 4, 4: 16}"

结果为：

{0: 0, 2: 4, 4: 16}