集合(set)

　　{‘a’,'b','c','d','e'}

　　定义：有不同元素组成的集合，集合是一组无序排列的可hash值，可以作为字段的key

　集合的创建:

　　定义可变量集合set >>> set_test=set('hello')

　　定义不可变量集合set >>> set_test=frozenset('hello')　　

　集合的关系测试

　　a = {'aa','bb','cc','dd'}

　　b = {'aa','bb','cc'}

　　交集：取两个集合相交的部分

a.intersection(b)
a&b

　　并集: 两个集合联合，去掉相同的部分

a.union(b)
a|b

　　差集:取一个集合在另一个集合没有的部分

a.difference(b)
a-b

　　交叉补集：联合两个集合，去掉共同的部分

a.symmetric_difference(b)
a^b

　　集合的方法：

class set(object):
    """
    set() -> new empty set object
    set(iterable) -> new set object

    Build an unordered collection of unique elements.
    """

    def add(self, *args, **kwargs):  # real signature unknown
        """添加一个元素到集合到集合中"""
        """
        Add an element to a set.

        This has no effect if the element is already present.
        """
        pass

    def clear(self, *args, **kwargs):  # real signature unknown
        """ Remove all elements from this set. """
        pass

    def copy(self, *args, **kwargs):  # real signature unknown
        """ Return a shallow copy of a set. """
        pass

    def difference(self, *args, **kwargs):  # real signature unknown
        """差集  a-b"""
        """
        Return the difference of two or more sets as a new set.

        (i.e. all elements that are in this set but not the others.)
        """
        pass

    def difference_update(self, *args, **kwargs):  # real signature unknown
        """取差集并更新集合"""
        """ Remove all elements of another set from this set. """
        pass

    def discard(self, *args, **kwargs):  # real signature unknown
        """删除元素，如果没找到，返回none"""
        """
        Remove an element from a set if it is a member.

        If the element is not a member, do nothing.
        """
        pass

    def intersection(self, *args, **kwargs):  # real signature unknown
        """交集 a&b"""
        """
        Return the intersection of two sets as a new set.

        (i.e. all elements that are in both sets.)
        """
        pass

    def intersection_update(self, *args, **kwargs):  # real signature unknown
        """取交集并更新集合"""
        """ Update a set with the intersection of itself and another. """
        pass

    def isdisjoint(self, *args, **kwargs):  # real signature unknown
        """判断两个交集是否有交集"""
        """ Return True if two sets have a null intersection. """
        pass

    def issubset(self, *args, **kwargs):  # real signature unknown
        """判断一个集合是不是另一个集合的子集"""
        """ Report whether another set contains this set. """
        pass

    def issuperset(self, *args, **kwargs):  # real signature unknown
        """判断一个集合是不是另一个集合的父集"""
        """ Report whether this set contains another set. """
        pass

    def pop(self, *args, **kwargs):  # real signature unknown
        """随机删除一个元素"""
        """
        Remove and return an arbitrary set element.
        Raises KeyError if the set is empty.
        """
        pass

    def remove(self, *args, **kwargs):  # real signature unknown
        """指定元素删除，如果没找到，报异常"""
        """
        Remove an element from a set; it must be a member.

        If the element is not a member, raise a KeyError.
        """
        pass

    def symmetric_difference(self, *args, **kwargs):  # real signature unknown
        """交叉补集 a^b"""
        """
        Return the symmetric difference of two sets as a new set.

        (i.e. all elements that are in exactly one of the sets.)
        """
        pass

    def symmetric_difference_update(self, *args, **kwargs):  # real signature unknown
        """取交叉补集并更新集合"""
        """ Update a set with the symmetric difference of itself and another. """
        pass

    def union(self, *args, **kwargs):  # real signature unknown
        """并集  a|b"""
        """
        Return the union of sets as a new set.

        (i.e. all elements that are in either set.)
        """
        pass

    def update(self, *args, **kwargs):  # real signature unknown
        """添加集合，参数为可迭代对象"""
        """ Update a set with the union of itself and others. """
        pass

set_method

字符串的格式化

　1. 百分号方式

　%[(name)[flags][width].[precision]tyecode]　　

(name) 　　【可选】用于指定key
flags 　　【可选】
- +　　右对齐：正数前加负号
- - 　左对齐：负数前加正号
- 空格　　右对齐
- 0 左对齐

width 【可选】指定宽度
.precision 【可选】小数点后保留位数
typecode 【必选】
- s 获取对象为str类型
- r 获取对象是可打印类型
- c　　将数字转换成unicode对应的值
- x 将整数转换成八进制表示
- d 将整数转换成十进制表示
- e 将整数，浮点数转换成科学表示法

test = 'i am %s' %'chen'

test = 'i am %s,age %d' %('hello',21)

test = 'i am %(name)s,age %(age)d' %{"name":'hello',"age":21}

test = 'i am %.2f' %27.22454

test = 'i am %(pp).2f' %{"pp":27.22454}

test = 'i am %(pp).2f  %%' %{"pp":27.22454} #打印百分号

　2. format方式

[[file]align][sign][#][0][width][,][.precision][type]

file 　【可选】空白处填充字符
align 【可选】对齐方式

< 内容左对齐
> 内容右对齐
^ 内容居中

sign 【可选】有无符号数字
- + 正号加负，负号加正
- - 正号不变，负号加正
- 空格正号空格，符号加负　　
# 【可选】对于二进制，八进制，十六进制，如果加上#，会显示0b/0o/0x，否则不显示
，【可选】为数字添加分割符
width 【可选】格式化位所占宽度
.precision 【可选】小数位保留精度
type 【可选】格式化类型

s 格式化字符串类型
空白同s 　
b 将十进制自动转化成二进制然后格式化
c 将十进制自动转化成对应的unicode字符
d 十进制整数
x 将十进制自动转换成十六进制然后格式化（小写x）
X　　将十进制自动转换成十六进制然后格式化（大写X）
e　将数字转换成科学计数法（小写e）
E 将数字转换成科学计数法（大写E）
f 转换成浮点型（默认小数后6位）
F　　转换成浮点型（默认小数后6位）
g 自动在e和f中切换
G 自动在E和F中切换
% 显示百分比（默认显示6位）

test = 'i am {}'.format("chen")

test = 'i am {},age {}'.format(*["chen",21])#一个*表示传列表

test = 'i am {1},age {0}'.format(21,"chen")

test = 'i am {name}'.format(name="chen")

test = 'i am {name}'.format(**{"name":"chen"})#两个*表示传字典

test = 'i am {0[0]},,age {0[1]}'.format(["chen",21])

test = 'i am {:s},,age {:d}'.format("chen",21)

test = 'i am {:s},,age {:d}'.format(*["chen",21])

test = 'i am {name:s},age {age:d}'.format(name="chen",age=21)

test = 'i am {name:s},age {age:d}'.format(**{"name":"chen","age":21})

test = 'numbers : {:b},{:o},{:d},{:x},{:X},{:%}'.format(15,15,15,15,15,0.15)

test = 'numbers : {0:b},{0:o},{0:d},{0:x},{0:X},{0:%}'.format(15)

test = 'numbers : {num:b},{num:o},{num:d},{num:x},{num:X},{num:%}'.format(num=15)

python之路（2）集合(set)和字符串格式化

前言