Python开发【第四篇】：Python基础之基础数据（补充）

三元运算

三元运算（三目运算），是对简单的条件语句的缩写。

# 书写格式
result = 值1 if 条件 else 值2
# 如果条件成立，那么将 “值1” 赋值给result变量，否则，将“值2”赋值给result变量

基本数据类型补充

set

set集合，是一个无序且不重复的元素集合

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
        """
        Add an element to a set，添加元素
         
        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. 清除内容"""
        pass
 
    def copy(self, *args, **kwargs): # real signature unknown
        """ Return a shallow copy of a set. 浅拷贝  """
        pass
 
    def difference(self, *args, **kwargs): # real signature unknown
        """
        Return the difference of two or more sets as a new set. A中存在，B中不存在
         
        (i.e. all elements that are in this set but not the others.)
        """
        pass
 
    def difference_update(self, *args, **kwargs): # real signature unknown
        """ Remove all elements of another set from this set.  从当前集合中删除和B中相同的元素"""
        pass
 
    def discard(self, *args, **kwargs): # real signature unknown
        """
        Remove an element from a set if it is a member.
         
        If the element is not a member, do nothing. 移除指定元素，不存在不保错
        """
        pass
 
    def intersection(self, *args, **kwargs): # real signature unknown
        """
        Return the intersection of two sets as a new set. 交集
         
        (i.e. all elements that are in both sets.)
        """
        pass
 
    def intersection_update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the intersection of itself and another.  取交集并更更新到A中 """
        pass
 
    def isdisjoint(self, *args, **kwargs): # real signature unknown
        """ Return True if two sets have a null intersection.  如果没有交集，返回True，否则返回False"""
        pass
 
    def issubset(self, *args, **kwargs): # real signature unknown
        """ Report whether another set contains this set.  是否是子序列"""
        pass
 
    def issuperset(self, *args, **kwargs): # real signature unknown
        """ Report whether this set contains another set. 是否是父序列"""
        pass
 
    def pop(self, *args, **kwargs): # real signature unknown
        """
        Remove and return an arbitrary set element.
        Raises KeyError if the set is empty. 移除元素
        """
        pass
 
    def remove(self, *args, **kwargs): # real signature unknown
        """
        Remove an element from a set; it must be a member.
         
        If the element is not a member, raise a KeyError. 移除指定元素，不存在保错
        """
        pass
 
    def symmetric_difference(self, *args, **kwargs): # real signature unknown
        """
        Return the symmetric difference of two sets as a new set.  对称差集
         
        (i.e. all elements that are in exactly one of the sets.)
        """
        pass
 
    def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the symmetric difference of itself and another. 对称差集，并更新到a中 """
        pass
 
    def union(self, *args, **kwargs): # real signature unknown
        """
        Return the union of sets as a new set.  并集
         
        (i.e. all elements that are in either set.)
        """
        pass
 
    def update(self, *args, **kwargs): # real signature unknown
        """ Update a set with the union of itself and others. 更新 """
        pass

练习：寻找差异

old_dict={
    "#1":22,
    "#2":33,
    "#3":55
}
new_dict={
    "#1":33,
    "#4":44,
    "#7":77
}
s1=set(old_dict.items())#将字典变成集合
s2=set(new_dict.items())
tmp=s1.difference(s2) #将s1中存在，s2中不存在的找出来
s1.difference_update(tmp)#将s1中的tmp集合删除掉
s1.update(s2)#将s2集合更新进s1
old_dict=dict(s1)
print(s1)

需要删除：？
需要新建：？
需要更新：？
注意：无需考虑内部元素是否改变，只要原来存在，新汇报也存在，就是需要更新

old_dict={
    "#1":22,
    "#2":33,
    "#3":55
}
new_dict={
    "#1":33,
    "#4":44,
    "#7":77
}
s1=set(old_dict.items())#将字典变成集合
s2=set(new_dict.items())
tmp=s1.difference(s2) #将s1中存在，s2中不存在的找出来
s1.difference_update(tmp)#将s1中的tmp集合删除掉
s1.update(s2)#将s2集合更新进s1
old_dict=dict(s1)
print(s1)

深浅拷贝

一、数字和字符串

在python中，字符串是一次性创建，不能被修改，只要修改都是再创建；list是链表形式，可以修改。

对于 数字 和 字符串 而言，赋值、浅拷贝和深拷贝无意义，因为其永远指向同一个内存地址。

import copy
# ######### 数字、字符串 #########
n1 = 123
# n1 = "i am alex age 10"
print(id(n1))
# ## 赋值 ##
n2 = n1
print(id(n2)) #n1和n2地址是一样的
# ## 浅拷贝 ##
n2 = copy.copy(n1)
print(id(n2)) #n1和n2地址是一样的
  
# ## 深拷贝 ##
n3 = copy.deepcopy(n1)
print(id(n3)) #n1和n2地址是一样的

二、其他基本数据类型

对于字典、元祖、列表 而言，进行赋值、浅拷贝和深拷贝时，其内存地址的变化是不同的。

1、赋值

赋值，只是创建一个变量，该变量指向原来内存地址，如：

n1 = {"k1": "wu", "k2": 123, "k3": ["alex", 456]}
  
n2 = n1

　　

2、浅拷贝

浅拷贝，在内存中只额外创建第一层数据，只是最外层内存地址变化

import copy
  
n1 = {"k1": "wu", "k2": 123, "k3": ["alex", 456]}
  
n3 = copy.copy(n1) #此时n1和n3的索引id不一样，但是两个列表中的元素的地址是一样的

 

拷贝:可以理解为复制。如上：将n1 的内存地址拷贝一份。然后跟n3关联起来。但是拷贝的时候只是第一层。（这个层数：可以根据数据的深度来定，比如字典，那就有两层）

3、深拷贝

深拷贝，在内存中将所有的数据重新创建一份（排除最后一层，即：python内部对字符串和数字的优化）

import copy
  
n1 = {"k1": "wu", "k2": 123, "k3": ["alex", 456]}
  
n4 = copy.deepcopy(n1)

通过上面的深浅拷贝，可以知道，拷贝深度不同，最终在改变n1和n3的值时候，带来的结果会有所不一样的

import copy
  
n1 = {"k1": "wu", "k2": 123, "k3": ["alex", 456]}

n4 = copy(n1)

n1['k1']="wwww" 

n1['k3'][0]="aaaa" 

print(n1) {"k1": "wwww", "k2": 123, "k3": ["aaaa", 456]} 

print(n4) {"k1": "wu", "k2": 123, "k3": ["aaaaa", 456]}

n4 = copy.deepcopy(n1) 
n1['k1']="wwww" 

n1['k3'][0]="aaaa" 

print(n1) {"k1": "wwww", "k2": 123, "k3": ["aaaa", 456]} 

print(n4) {"k1": "wu", "k2": 123, "k3": ["alex", 456]}