数据入门

原子数据类型

>>> True
True
>>> False
False
>>> False or True
True
>>> not (False or True)
False
>>> True and True
True

>>> theSum=0
>>> theSum
0
>>> theSum=theSum+1
>>> theSum
1
>>> theSum=True
>>> theSum
True

赋值语句theSum=0创建一个变量theSum并让它持有对数据对象0的引用。通常对语句右侧进行求值，并将对结果数据对象的引用"赋值"给左侧名称。如果数据的类型发生变化，那么变量的类型也是如此。赋值语句改变了变量所持有的引用。

内置集合数据类型

>>> [1,3,True,6.5]
[1, 3, True, 6.5]
>>> mylist=[1,3,True,6.5]
>>> mylist
[1, 3, True, 6.5]

通过重复操作初始化一个列表

>>> myList=[0]*6
>>> myList
[0, 0, 0, 0, 0, 0]

>>> myList=[1,2,3,4]
>>> A=[myList]*3
>>> print(A)
[[1, 2, 3, 4], [1, 2, 3, 4], [1, 2, 3, 4]]
>>> myList[2]=45
>>> print(A)
[[1, 2, 45, 4], [1, 2, 45, 4], [1, 2, 45, 4]]

>>> myList=[1024,3,True,6.5]
>>> myList.append(False)
>>> print(myList)
[1024, 3, True, 6.5, False]
>>> myList.insert(2,4.5)
>>> print(myList)
[1024, 3, 4.5, True, 6.5, False]
>>> print(myList.pop())
False
>>> print(myList)
[1024, 3, 4.5, True, 6.5]
>>> print(myList.pop(1))
3
>>> print(myList)
[1024, 4.5, True, 6.5]
>>> print(myList.pop(2))
True
>>> print(myList)
[1024, 4.5, 6.5]
>>> myList.sort()
>>> print(myList)
[4.5, 6.5, 1024]
>>> myList.reverse()
>>> print(myList)
[1024, 6.5, 4.5]
>>> print(myList.count(6.5))
1
>>> print(myList.index(4.5))
2
>>> myList.remove(6.5)
>>> print(myList)
[1024, 4.5]
>>> del myList[0]
>>> print(myList)
[4.5]

range函数

>>> range(10)
range(0, 10)
>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(5,10)
range(5, 10)
>>> list(range(5,10))
[5, 6, 7, 8, 9]
>>> list(range(5,10,2))
[5, 7, 9]
>>> list(range(10,1,-1))
[10, 9, 8, 7, 6, 5, 4, 3, 2]

字符串是由零个或多个字母、数字和其他符号组成的序列集合。我们称之为字母，数字和其他符号字符。通过使用引号（单引号或双引号）将中文字符串值与标识符区分开。

>>> "David"
'David'
>>> myName="David"
>>> myName[3]
'i'
>>> myName*2
'DavidDavid'
>>> len(myName)
5

字符串的其他方法

>>> myName
'David'
>>> myName.upper()
'DAVID'
>>> myName.center(10)
'  David   '
>>> myName.find('v')
2
>>> myName.split('v')
['Da', 'id']

列表与字符串之间的主要区别是，列表可以被修改，而字符串不能。

>>> myList
[1, 3, True, 6.5]
>>> myList[0]=2**10
>>> myList
[1024, 3, True, 6.5]
>>> myName
'David'
>>> myName[0]='X'
Traceback (most recent call last):File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

元组与列表非常相似，但元组不可变。

>>> myTuple=(2,True,4.96)
>>> myTuple
(2, True, 4.96)
>>> len(myTuple)
3
>>> myTuple[0]
2
>>> myTuple*3
(2, True, 4.96, 2, True, 4.96, 2, True, 4.96)
>>> myTuple[0:2]
(2, True)

修改元组之后的报错信息

>>> myTuple[1]=False
Traceback (most recent call last):File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> 

set是一个无序的，为空或是更多不可变Python数据对象集合。集合中的值不允许重复，以逗号分割，写在大括号中。空集合用set()表示。集合是异构的并且可以被分配给一个变量。

>>> {3,6,"cat",4.5,False}
{False, 3, 4.5, 'cat', 6}
>>> mySet={3,6,"cat",4.5,False}
>>> mySet
{False, 3, 4.5, 'cat', 6}

集合支持的操作

>>> mySet
{False, 3, 4.5, 'cat', 6}
>>> len(mySet)
5
>>> False in mySet
True
>>> "dog" in mySet
False

集合的方法

>>> mySet
{False, 3, 4.5, 'cat', 6}
>>> yourSet={99,3,100}
>>> mySet.union(yourSet)
{False, 3, 4.5, 'cat', 6, 99, 100}
>>> mySet | yourSet
{False, 3, 4.5, 'cat', 6, 99, 100}
>>> mySet.intersection(yourSet)
{3}
>>> mySet & yourSet
{3}
>>> mySet.difference(yourSet)
{False, 4.5, 'cat', 6}
>>> mySet-yourSet
{False, 4.5, 'cat', 6}
>>> {3,100}.issubset(yourSet)
True
>>> {3,100}<=yourSet
True
>>> mySet.add("house")
>>> mySet
{False, 3, 4.5, 'cat', 6, 'house'}
>>> mySet.pop()
False
>>> mySet
{3, 4.5, 'cat', 6, 'house'}
>>> mySet.clear()
>>> mySet
set()

最后一个无序的Python集合——字典

>>> capitals={'Iowa':'DesMoines','Wisconsin':'Madison'}
>>> capitals
{'Iowa': 'DesMoines', 'Wisconsin': 'Madison'}
>>> 

通过键来访问值

>>> capitals={'Iowa':'DesMoines','Wisconsin':'Madison'}
>>> capitals
{'Iowa': 'DesMoines', 'Wisconsin': 'Madison'}
>>> capitals={'Iowa':'DesMoines','Wisconsin':'Madison'}
>>> print(capitals['Iowa'])
DesMoines
>>> capitals['Utah']='SaltLakeCity'
>>> print(capitals)
{'Iowa': 'DesMoines', 'Wisconsin': 'Madison', 'Utah': 'SaltLakeCity'}
>>> capitals['California']='Sacramento'
>>> print(len(capitals))
4
>>> for k in capitals:
...     print(capitals[k]," is the capital of ",k)
... 
DesMoines  is the capital of  Iowa
Madison  is the capital of  Wisconsin
SaltLakeCity  is the capital of  Utah
Sacramento  is the capital of  California

字典上没有特定的顺序

>>> phoneext={'david':1410,'brad':1137}
>>> phoneext
{'david': 1410, 'brad': 1137}
>>> phoneext.keys()
dict_keys(['david', 'brad'])
>>> list(phoneext.keys())
['david', 'brad']
>>> phoneext.values()
dict_values([1410, 1137])
>>> list(phoneext.values())
[1410, 1137]
>>> phoneext.items()
dict_items([('david', 1410), ('brad', 1137)])
>>> list(phoneext.items())
[('david', 1410), ('brad', 1137)]
>>> phoneext.get("kent")
>>> phoneext.get("kent","NO ENTRY")
'NO ENTRY'