关于python:Python魔法函数

1.什么是魔法函数

魔法函数即Python类中以__（双下划线）结尾，以__（双下划线）结尾的函数，Python提供的函数，能够让咱们随便定义类的个性
示例：

class Company(object):
    def __init__(self, employee_list):
        self.employee = employee_list
    def __getitem__(self, item):
        return self.employee[item]
company = Company(["Tom", "Jerry", "Bob"])
# 没有__getitem__时，通过这种形式遍历Company类中的employee
for em in company.employee:
    print(em)
# 自定义__getitem__后，Company变为可迭代对象
for em in company:
    print(em)

代码中的__init__、__getitem__即为魔法函数

2.Python的数据模型以及数据模型对Python的影响

魔法函数自身是Python的数据模型，魔法函数是网络风行的叫法
以__len__为例阐明数据模型（魔法函数）对Python的影响

class Company(object):
    def __init__(self, employee_list):
        self.employee = employee_list
    def __getitem__(self, item):
        return self.employee[item]
    def __len__(self):
        return len(self.employee)
company = Company(["Tom", "Jerry", "Bob"])
# 不定义__len__是无奈应用len()的
print(len(company))

3.Python魔法函数一览（个别阐明）

3.1非数学运算

字符串示意__repr__、__str__

• __str__：对对象进行字符串格式化

class Company(object):
    def __init__(self, employee_list):
        self.employee = employee_list
company = Company(["Tom", "Jerry", "Bob"])      
print(company)  # 在Python解释器中会隐含调用str,即print(str(company))

此时输入：<__main__.Company object at 0x000001D53A322D30>
验证解释器隐含调用str

class Company(object):
    def __init__(self, employee_list):
        self.employee = employee_list
        
    def __str__(self):
        return ','.join(self.employee)
company = Company(["Tom", "Jerry", "Bob"])      
print(company)

输入：Tom,Jerry,Bob

• __repr__:开发模式才会用到

class Company(object):
    def __init__(self, employee_list):
        self.employee = employee_list
        
company = Company(["Tom", "Jerry", "Bob"])      
company   # 在Python解释器中会隐含调用repr,即repr(company),在Python外部为company.__repr__()

此时输入：<__main__.Company at 0x1d53a2d3a58>
验证解释器隐含调用repr

class Company(object):
    def __init__(self, employee_list):
        self.employee = employee_list
        
    def __repr__(self):
        return ','.join(self.employee)
company = Company(["Tom", "Jerry", "Bob"])      
company   

输入：Tom,Jerry,Bob

3.2数学运算

• pass