Introducing Python Dictionaries

下面来通过实例学习一下 Python 内置的 Dictionaries 类型，及其常用操作符、表达式等。以及随机数的操作。

Operators

$ python
Python 2.7.5 (default, Aug 25 2013, 00:04:04)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

# 空 dict
>>> books = {}

# 赋值
>>> books['Ruby'] = 'Matz'
>>> books['Python'] = 'Guido'
>>> books['Java'] = 'James'
>>> books
{'Python': 'Guido', 'Java': 'James', 'Ruby': 'Matz'}

Methods

>>> books = {'Python': 'Guido', 'Java': 'James', 'Ruby': 'Matz'}
>>> books
{'Python': 'Guido', 'Java': 'James', 'Ruby': 'Matz'}

# 获取 dict keys
>>> books.keys()
['Python', 'Java', 'Ruby']

# 获取 dict values
>>> books.values()
['Guido', 'James', 'Matz']

# 判断 key 是否存在
>>> books.has_key('ruby')
False
>>> books.has_key('Ruby')
True
>>> books.has_key('C')
False

# 读取 key 对应的 value
>>> books["Ruby"]
'Matz'
>>> books.get('Ruby')
'Matz'
>>> print books.get('C')
None
>>> books["C"]
Traceback (most recent call last):
  File "< stdin >", line 1, in < module >
KeyError: 'C'

# 删除 key 对应的 value
>>> print books.pop('Ruby')
Matz
>>> books
{'Python': 'Guido', 'Java': 'James'}
>>> del(books['Java'])
>>> books
{'Python': 'Guido'}


# 遍历 dict
>>> for key,value in books.iteritems():
...   print "Book name %s and author %s" %(key, value)
...
Book name Python and author Guido
Book name Java and author James
Book name Ruby and author Matz


# creates a new dictionary with keys from seq and values set to value.
days = 3
s1 = dict.fromkeys(xrange(days))
>>> s1
{0: None, 1: None, 2: None}

>>> days = 3
>>> value = []
>>>
>>> t = {day:list(value) for day in xrange(days)}
>>> t
{0: [], 1: [], 2: []}
>>> t[0].append(0)
>>> t[1].append(1)
>>> t
{0: [0], 1: [1], 2: []}
>>>

Tips

# 对 dict 进行字典排序
>>> provinces = [{"pinyin": "SHANGHAI"},
...     {"pinyin": "JIANGSU"},
...     {"pinyin": "FUJIAN"},
...     {"pinyin": "HEILONGJIANG"},
...     {"pinyin": "ANHUI"}]
>>> provinces
[{'pinyin': 'SHANGHAI'}, {'pinyin': 'JIANGSU'}, {'pinyin': 'FUJIAN'}, {'pinyin': 'HEILONGJIANG'}, {'pinyin': 'ANHUI'}]
>>> sorted_provinces = sorted(provinces, key=lambda k: k['pinyin'])
>>> sorted_provinces
[{'pinyin': 'ANHUI'}, {'pinyin': 'FUJIAN'}, {'pinyin': 'HEILONGJIANG'}, {'pinyin': 'JIANGSU'}, {'pinyin': 'SHANGHAI'}]

2014-05-16