Henry's Blog

Introducing Python Tuples

Python 内置的 Tuples 类型，是一个比较特殊的数据类型，兼有 List 和 String 的特性：可以包含多种类型，是不可变的序列。正是由于它是不可变的序列， 在 Django 中，常用作 settings 的配置。

下面来通过实例学习一下 Python 内置的 Tuples 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
>>> empty_tuple = ()
>>> empty_tuple
()
>>> empty_tuple.__class__
< type 'tuple' >

# 仅包含一个值，需要以 , 结尾
>>> t = (1)
>>> t
1
>>> t.__class__
< type 'int' >
>>> t = (1,)
>>> t
(1,)
>>> t.__class__
< type 'tuple' >

# 赋值/取值操作
>>> fool_tuple = (1, 'Api', False)
>>> fool_tuple
(1, 'Api', False)
>>> fool_tuple.index('Api')
1
>>> fool_tuple[1]
'Api'


# 不能改变 value
>>> fool_tuple[0] = 'a'
Traceback (most recent call last):
  File "< stdin >", line 1, in < module >
TypeError: 'tuple' object does not support item assignment

Methods

>>> fool_tuple = (1, 'Api', False)

# 计算长度
>>> len(fool_tuple)
3

# 计算 value 出现次数
>>> fool_tuple.count('Api')
1

# 循环输出
>>> for x in fool_tuple: print x,
...
1 Api False

# 排序
>>> sorted(fool_tuple)
[False, 1, 'Api']

# list 转换
>>> fool_list = list(fool_tuple)
>>> fool_list
[1, 'Api', False]
>>> tuple(fool_list)
(1, 'Api', False)

# dict 操作
>>> student = dict(name='Henry', age=25, skills=['Ruby', 'Python'])
>>> student
{'skills': ['Ruby', 'Python'], 'age': 25, 'name': 'Henry'}
>>> tuple(student.values())
(['Ruby', 'Python'], 25, 'Henry')
>>> tuple(student.items())
(('skills', ['Ruby', 'Python']), ('age', 25), ('name', 'Henry'))
>>> tuple(student.items())[0][0]
'skills'

Tips

Tuples 在 Django 中的应用。 

# settings
# Application definition
INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'api',
    'south',
    'rest_framework',
)

# Model choices
# requirements
django-model-utils==2.0

# Guide Model status field

STATUS_CHOICES = Choices(
    (0, 'pending', 'pending'),
    (1, 'succeeded', 'succeeded'),
    (2, 'failed', 'failed'),
)

status = models.IntegerField(choices=STATUS_CHOICES,
    default=STATUS_CHOICES.pending)

2014-05-19

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