python基础学习笔记3

Python一切皆对象，但同时，Python还是一个多范式语言(multi-paradigm),你不仅可以使用面向对象的方式来编写程序，还可以用面向过程的方式来编写相同功能的程序(还有函数式、声明式等，我们暂不深入)。Python的多范式依赖于Python对象中的特殊方法(special method)。

特殊方法名的前后各有两个下划线。特殊方法又被成为魔法方法(magic method)，定义了许多Python语法和表达方式，正如我们在下面的例子中将要看到的。当对象中定义了特殊方法的时候，Python也会对它们有“特殊优待”。比如定义了__init__()方法的类，会在创建对象的时候自动执行__init__()方法中的操作。

# without context manager
f = open("new.txt", "w")
print(f.closed)               # whether the file is open
f.write("Hello World!")
f.close()
print(f.closed)

# with context manager
with open("new.txt", "w") as f:
    print(f.closed)
    f.write("Hello World!")
print(f.closed)

def line_conf():
    def line(x):
        return 2*x+1
    return line          # return a function object

my_line = line_conf()
print(my_line(5))

def line_conf():
    b = 15
    def line(x):
        return 2*x+b
    return line            # return a function object
b = 5
my_line = line_conf()
print(my_line(5))

def line_conf(a, b):
    def line(x):
        return ax + b
    return line

line1 = line_conf(1, 1)
line2 = line_conf(4, 5)
print(line1(5), line2(5))

# get square sumdef square_sum(a, b):
    return a**2 + b**2
# get square diffdef square_diff(a, b):
    return a**2 - b**2
print(square_sum(3, 4))

# modify: print input

# get square sumdef square_sum(a, b):
    print("intput:", a, b)
    return a**2 + b**2

# get square diffdef square_diff(a, b):
    print("input", a, b)
    return a**2 - b**2

print(square_sum(3, 4))
print(square_diff(3, 4))

def decorator(F):
    def new_F(a, b):
        print("input", a, b)
        return F(a, b)
    return new_F

# get square sum@decorator
def square_sum(a, b):
    return a**2 + b**2

# get square diff@decorator
def square_diff(a, b):
    return a**2 - b**2

print(square_sum(3, 4))
print(square_diff(3, 4))