标签：iterator [46] mapping object iterable int call ems float
返回对象的唯一标识，Cpython中返回的是对象的内存地址
In [1]: id("a")
Out[1]: 139855651366088
In [5]: b = range(5)
In [6]: id(b)
Out[6]: 139855403437920返回的是对象的hash值
In [7]: hash(‘a‘)
Out[7]: -1064091420252831392
In [8]: hash(1)
Out[8]: 1
In [9]: hash(2000)
Out[9]: 2000
In [10]: hash(range(5))
Out[10]: 7573308626029640035
In [11]: hash([1,2])
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-11-9ce67481a686> in <module>
----> 1 hash([1,2])
TypeError: unhashable type: ‘list‘
In [12]: hash({1,2})
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-12-d49f6de35e1d> in <module>
----> 1 hash({1,2})
TypeError: unhashable type: ‘set‘
In [13]: hash({"a":1,"b":2})
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-13-252784143f1f> in <module>
----> 1 hash({"a":1,"b":2})返回的是对象的类型
In [14]: type(1)
Out[14]: int
In [15]: type("a")
Out[15]: str
In [16]: type([1,2])
Out[16]: list
In [17]: type({1,2})
Out[17]: set
In [18]: type({"a":1,"b":2})
Out[18]: dict
In [19]: type(range(5))
Out[19]: range转换浮点型
In [30]: float(10)
Out[30]: 10.0转换为整型(只取整数部分)
In [32]: int(10.12141)
Out[32]: 10
In [33]: int(10.92141)
Out[33]: 10转换为二进制
In [34]: bin(7)
Out[34]: ‘0b111‘转换为十六进制
In [35]: hex(16)
Out[35]: ‘0x10‘
In [36]: hex(15)
Out[36]: ‘0xf‘转换为8进制
In [38]: oct(8)
Out[38]: ‘0o10‘
In [39]: oct(7)
Out[39]: ‘0o7‘
In [40]: oct(9)
Out[40]: ‘0o11‘
In [41]: oct(16)
Out[41]: ‘0o20‘
In [42]: oct(32)
Out[42]: ‘0o40‘转换为布尔型
In [43]: bool("a")
Out[43]: True
In [44]: bool(2)
Out[44]: True
In [45]: bool(1)
Out[45]: True
In [46]: bool(0)
Out[46]: False
In [47]: bool(None)
Out[47]: False
In [48]: bool(‘‘)
Out[48]: False
In [49]: bool(-1)
Out[49]: True转换为列表(需要是可迭代对象)
In [50]: list(range(5))
Out[50]: [0, 1, 2, 3, 4]
In [51]: list((1,2,3,4))
Out[51]: [1, 2, 3, 4]转换为元组
tuple(iterable) -> tuple initialized from iterable‘s items
If the argument is a tuple, the return value is the same object.
In [53]: tuple([1,2,3,4])
Out[53]: (1, 2, 3, 4)
In [55]: tuple((1,2,3,4))
Out[55]: (1, 2, 3, 4)转换为字典
dict() -> new empty dictionary
dict(mapping) -> new dictionary initialized from a mapping object‘s
(key, value) pairs
dict(iterable) -> new dictionary initialized as if via:
d = {}
for k, v in iterable:
d[k] = v
dict(**kwargs) -> new dictionary initialized with the name=value pairs in the keyword argument list. For example: dict(one=1, two=2) back to top
定义一个空字典
d = dict() 或者 d = {}
使用 name=value 对儿初始化一个字典
scm = dict(a=1,b=2)
使用**可迭代对象**和**name=value对**构造字典，不过可迭代对象的元素必须是一个**二元结构**
dict(iterable,\*\*kwarg)
scm = dict((("a",3),("b",4)))
scm = dict([("a",5),("b",6)])
scm = dict({["a",7],["b",8]}) # 错误，set中不能有不可hash的对象，[]不可hash
scm = dict([("a",33),("b",44)],x = 00, y = 11)
scm = dict([["a",55],["b",66]],x = 22, y = 33)
scm = dict(((["a"],3),("b",4))) # 错误，key中不能有不可hash的对象
使用mapping 构造字典
dict(mapping,\*\*kwarg)
scm = dict(scm2) # 使用字典scm2构建字典scm
In [74]: a = dict(enumerate(range(5)))
In [75]: a
Out[75]: {0: 0, 1: 1, 2: 2, 3: 3, 4: 4}
直接使用键值对创建字典
scm = {"a":1,"b":"test","c":None,"d":[1,2,3],"e":{1,2,3},"f":{"a":1,1:"new"}}
通过类方法构建字典 **dict.fromkeys(iterable,value)** dict.fromkeys(iterable,value),value是设置的默认值，不指定就是None
scm = dict.fromkeys(range(5)) <==> scm = dict.fromkeys(range(5),None)
scm = dict.fromkeys(range(5),0)
scm = dict.fromkeys(range(5),"test")演示
In [1]: scm = dict(a=1,b=2)
In [2]: scm
Out[2]: {‘a‘: 1, ‘b‘: 2}
==============================================================
In [7]: scm = dict((("a",3),("b",4)))
In [8]: scm
Out[8]: {‘a‘: 3, ‘b‘: 4}
==============================================================
In [9]: scm = dict([("a",5),("b",6)])
In [10]: scm
Out[10]: {‘a‘: 5, ‘b‘: 6}
==============================================================
In [11]: scm = dict({["a",7],["b",8]})
#--------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-11-308a59daea34> in <module>
----> 1 scm = dict({["a",7],["b",8]})
TypeError: unhashable type: ‘list‘
==============================================================
In [12]: scm = dict([("a",33),("b",44)],x = 00, y = 11)
In [13]: scm
Out[13]: {‘a‘: 33, ‘b‘: 44, ‘x‘: 0, ‘y‘: 11}
==============================================================
In [14]: scm = dict([["a",55],["b",66]],x = 22, y = 33)
In [15]: scm
Out[15]: {‘a‘: 55, ‘b‘: 66, ‘x‘: 22, ‘y‘: 33}
==============================================================
In [17]: scm = dict(((["a"],3),("b",4)))
#--------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-17-6a1a945e115a> in <module>
----> 1 scm = dict(((["a"],3),("b",4)))
TypeError: unhashable type: ‘list‘
==============================================================
In [11]: scm
Out[11]: {‘a‘: 55, ‘b‘: 66, ‘x‘: 22, ‘y‘: 33}
In [12]: scm2 = dict(scm)
In [13]: scm2
Out[13]: {‘a‘: 55, ‘b‘: 66, ‘x‘: 22, ‘y‘: 33}
==============================================================
In [14]: scm = {"a":1,"b":"test","c":None,"d":[1,2,3],"e":{1,2,3},"f":{"a":1,1:"new"}}
In [15]: scm
Out[15]:
{‘a‘: 1,
‘b‘: ‘test‘,
‘c‘: None,
‘d‘: [1, 2, 3],
‘e‘: {1, 2, 3},
‘f‘: {‘a‘: 1, 1: ‘new‘}}
==============================================================
In [16]: scm = dict.fromkeys(range(5))
In [17]: scm
Out[17]: {0: None, 1: None, 2: None, 3: None, 4: None}
In [18]: scm = dict.fromkeys(range(5),0)
In [19]: scm
Out[19]: {0: 0, 1: 0, 2: 0, 3: 0, 4: 0}
In [20]: scm = dict.fromkeys(range(5),"test")
In [21]: scm
Out[21]: {0: ‘test‘, 1: ‘test‘, 2: ‘test‘, 3: ‘test‘, 4: ‘test‘}
In [22]: scm = dict.fromkeys(range(5),None)
In [23]: scm
Out[23]: {0: None, 1: None, 2: None, 3: None, 4: None}转换为集合
set() -> new empty set object
set(iterable) -> new set object
In [77]: set([1,2,3,4])
Out[77]: {1, 2, 3, 4}
In [78]: set(range(5))
Out[78]: {0, 1, 2, 3, 4}转换为复数
In [81]: complex(1)
Out[81]: (1+0j)
In [82]: complex(-1)
Out[82]: (-1+0j)
In [83]: complex(-1,2)
Out[83]: (-1+2j)转换为字节 back to top
In [85]: bytes(range(97,123))
Out[85]: b‘abcdefghijklmnopqrstuvwxyz‘
In [86]: bytes([97,98,99])
Out[86]: b‘abc‘
In [87]: bytes({97,98,99})
In [89]: bytes(b"abc")
Out[89]: b‘abc‘
In [90]: bytes("abc".encode())
In [91]: bytes()
Out[91]: b‘‘转换为bytearray
In [93]: bytearray(range(97,123))
Out[93]: bytearray(b‘abcdefghijklmnopqrstuvwxyz‘)
In [94]: bytearray([97,98,99])
Out[94]: bytearray(b‘abc‘)
In [95]: bytearray({97,98,99})
Out[95]: bytearray(b‘abc‘)
In [96]: bytearray(b"abc")
Out[96]: bytearray(b‘abc‘)
In [97]: bytearray("abc".encode())
Out[97]: bytearray(b‘abc‘)接收用户输入，返回一个字符串
In [100]: input()
123
Out[100]: ‘123‘
In [101]: input(">>>")
>>123
Out[101]: ‘123‘打印输出，可以指定分隔符和换行符，默认是以空格分隔，换行结尾，输出到控制台，返回值是 None.
In [102]: print(123)
123
In [103]: print("123")
123
In [106]: print("123","456",sep=" ")
123 456
## 这里有换行
In [109]: print("123","456",sep=" ",end="")
123 456 # 这里咩有换行
In [110]: 求对象的长度，对象是一个容器，不能是生成器迭代器
In [110]: len(range(5))
Out[110]: 5
In [111]: len(( i for i in range(5)))
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-111-b60955f7c630> in <module>
----> 1 len(( i for i in range(5)))
TypeError: object of type ‘generator‘ has no len()
In [112]: len([ i for i in range(5)])
Out[112]: 5
In [113]: iter([1,2,3])
Out[113]: <list_iterator at 0x7f329f280c50>
In [114]: len(iter([1,2,3]))
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-114-f71e648375a5> in <module>
----> 1 len(iter([1,2,3]))
TypeError: object of type ‘list_iterator‘ has no len()判断对象obj是否属于某种类型或者元组中列出的某个类型
isinstace(cls,class_or_tuple)
In [115]: isinstance(1, int)
Out[115]: True
In [116]: isinstance(1, (int,str,list))
Out[116]: True
In [117]: isinstance([1,2,3], (int,str,list))
Out[117]: True
In [118]: isinstance({1,2,3}, (int,str,list))
Out[118]: False
In [119]: isinstance({1,2,3}, (int,set))
Out[119]: True判断类型cls是否是某种类型的子类或元组中列出的某个类型的子类
issubclass(bool,int)
issubclass(bool,(int,str,float,bool))
In [122]: issubclass(bool,int)
Out[122]: True
In [123]: issubclass(bool,(int,str,float,bool))
Out[123]: True绝对值
In [124]: abs(1)
Out[124]: 1
In [125]: abs(-1)
Out[125]: 1
In [126]: abs(-1 +1j)
Out[126]: 1.4142135623730951
In [127]: abs(-1 -1j)
Out[127]: 1.4142135623730951返回可迭代对象中最大
In [130]: max([1,2,3,4])
Out[130]: 4
In [131]: max(range(5))
Out[131]: 4
In [132]: max(1,2,3) 返回可迭代对象中最小值
In [133]: min([1,2,3,4])
Out[133]: 1
In [134]: min(range(5))
Out[134]: 0
In [135]: min(1,2,3)
Out[135]: 1round(number[, ndigits]) -> number
取整，原则是四舍六入五取偶
round(3.1234,2)
In [1]: round(3.1234,2) # ndigits 是指定精度
Out[1]: 3.12
In [136]: round(3.5)
Out[136]: 4
In [137]: round(2.5)
Out[137]: 2
In [138]: round(2.50001)幂运算
Equivalent to xy (with two arguments) or xy % z (with three arguments)
In [140]: pow(2,3)
Out[140]: 8
In [141]: pow(2,-3)
Out[141]: 0.125从0开始到stop-1的可迭代对象；
range(start, stop[, step])从start开始到stop-1结束步长为step的可迭代对象
In [145]: [ i for i in range(10)]
Out[145]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
In [146]: [ i for i in range(5,10)]
Out[146]: [5, 6, 7, 8, 9]
In [147]: [ i for i in range(5,10,2)]
Out[147]: [5, 7, 9]
In [148]: [ i for i in range(5,10,-1)]
Out[148]: []
In [149]: [ i for i in range(5,1,-1)]
Out[149]: [5, 4, 3, 2]连整除带取模
等价于tuple (x//y, x%y)
In [150]: divmod(2,3)
Out[150]: (0, 2)对可迭代对象的所有元素求和
sum(range(1,20,2))
=====================
In [151]: sum(range(1,20,2))
Out[151]: 100
In [152]: sum(range(10))
Out[152]: 45
In [153]: sum(range(10),100)
Out[153]: 145给一个一定范围的整数返回对应的字符
chr(97)
chr(20013)
=====================
In [154]: chr(97)
Out[154]: ‘a‘
In [155]: chr(20013)
Out[155]: ‘中‘返回字符对应的整数
ord(‘a‘)
ord(‘中‘)
=====================
In [156]: ord(‘a‘)
Out[156]: 97
In [157]: ord(‘中‘)
Out[157]: 20013待续
待续
待续
Signature: sorted(iterable, /, *, key=None, reverse=False)
Return a new list containing all items from the iterable in ascending order.
sorted((1,2,3,4,5,"a","b"), key=str, reverse=True)
=============
In [2]: sorted((1,2,3,4,5,"a","b"), key=str, reverse=True)
Out[2]: [‘b‘, ‘a‘, 5, 4, 3, 2, 1]翻转,返回一个翻转元素的迭代器
不会就地修改。而是倒着去取元素，只能对线性结构的数据进行反转
list(reversed("13579"))
{ reversed((2, 4)) } # 有几个元素？只有一个元素： {<reversed at 0x7fcab92c1cf8>}
for x in reversed([‘c‘,‘b‘,‘a‘]):
print(x)
reversed(sorted({1, 5, 9}))In [4]: reversed(sorted({1, 5, 9}))
Out[4]: <list_reverseiterator at 0x7fcab92c1978>In [1]: for i in reversed(sorted({1, 5, 9})) :
...: print(i)
9
5
1枚举，迭代一个序列，返回索引数字和元素构成的二元组，
start表示索引开始的数字，默认是0
In [10]: for i in enumerate(range(4)):
...: print(i)
...:
(0, 0)
(1, 1)
(2, 2)
(3, 3)
In [11]: for i in enumerate("abcdefg"):
...: print(i,end=‘ ‘)
...:
(0, ‘a‘) (1, ‘b‘) (2, ‘c‘) (3, ‘d‘) (4, ‘e‘) (5, ‘f‘) (6, ‘g‘) iter将一个可迭代对象封装成一个迭代器
In [160]: iter([1,2,3,4])
Out[160]: <list_iterator at 0x7f329dde7780>
In [161]: a = iter([1,2,3,4])
In [162]: for i in a:
...: print(i)
...:
1
2
3
4取元素,next对一个迭代器取下一个元素。如果全部元素都取过了，再次next会抛StopIteration异常
判断一个对象是不是一个迭代器，通过next()就可以测试出来
range对象虽然是一个可迭代对象，但并不是一个迭代器
In [12]: a = range(5)
In [13]: next(a)
-----------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-13-15841f3f11d4> in <module>
----> 1 next(a)
TypeError: ‘range‘ object is not an iteratorreversed()函数返回的就是一个迭代器
In [14]: a = reversed(range(5))
In [15]: next(a)
Out[15]: 4
In [16]: next(a)
Out[16]: 3
In [17]: next(a)
Out[17]: 2
In [18]: next(a)
Out[18]: 1
In [19]: next(a)
Out[19]: 0
In [20]: next(a)
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-20-15841f3f11d4> in <module>
----> 1 next(a)
StopIteration: 能够通过迭代一次次返回不同的元素的对象
list, tuple, string, bytes, bytearray, range, set, dict, 生成器
可以使用成员操作符 in , not in, in 和 not in本质上就是在对可迭代对象进行遍历
1 in range(5)
3 in ( i for i in range(5))
3 in { x:y for x,y in zip(range(4),range(4,10)) }In [21]: 3 in ( i for i in range(5))
Out[21]: True
In [23]: 3 in { x:y for x,y in zip(range(4),range(4,10)) }
Out[23]: TrueIn [24]: type(range(5))
Out[24]: range
In [25]: type(iter(range(5)))
Out[25]: range_iterator
In [27]: for i in iter(range(5)):
...: print(i)
...:
0
1
2
3
4In [28]: g = ( x for x in range(5) )
In [29]: print(type(g))
<class ‘generator‘>
In [30]: print(next(g))
0
In [31]: print(next(g))
1
In [32]: print(next(g))
2
In [33]: print(next(g))
3
In [34]: print(next(g))
4
In [35]: print(next(g))
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-35-1dfb29d6357e> in <module>
----> 1 print(next(g))
StopIteration: 本文链接：https://www.cnblogs.com/shichangming/p/10264132.html
标签：iterator [46] mapping object iterable int call ems float
原文地址：https://www.cnblogs.com/shichangming/p/10264132.html
