python 之 深入理解

# 一旦遇到第一个return，函数执行就会停止
def three():
    print(1)
    return 2
    print(3)
    return 22 
 
three()
print(4)

----------------------

for i in range(10):
    line = ""
    for j in range(10):
        if i == j:
            break
        line += "{} ".format(j)
    print(line)
-----------------------

魔法函数
__init__ :初始化类的新实例 Initialize a new instance of the class
__new__ :创建该类的新实例 Create a new instance of the class
__repr__ :定义实例表示进行调试 Define an instance representation for debugging
__str__ :定义实例的用户友好表示 Define user-friendly representation of an instance

class Song:
    def __init__(self, artist, name, year):
        self.artist = artist
        self.name = name
        self.year = year
 
    def __repr__(self):
        rep = "Artist: {}. Name: {}. Year: {}".format(self.artist, self.name,
                                                      self.year)
        return rep
 
    def __str__(self):
        return "{} — {} ({})".format(self.artist, self.name, self.year)
    
dsmn = Song("Queen", "Don't stop me now", 1979)
print(dsmn)


----------
# 如果不使用global关键字，则无法在函数内部更改全局变量的值

x = "global"
def outer():
    x = "outer local"
    def inner():
        x = "inner local"
        def func():
            x = "func local"
            print(x)
        func()
    inner()
 

# nonlocal 关键字可让我们将变量分配给外部（而非全局）范围

def func():
    x = 1
    def inner():
        x = 2
        print("inner:", x)
    inner()
    print("outer:", x)
 
def nonlocal_func():
    x = 1
    def inner():
        nonlocal x
        x = 2
        print("inner:", x)
    inner()
    print("outer:", x)
 
func()  # inner: 2
        # outer: 1
 
nonlocal_func()  # inner: 2
                 # outer: 2

outer()

---------------------------------

def func(positional_args, args_with_default, *args, **kwargs):
    pass


print(*"fun")        # f u n
print(*[5, 10, 15])  # 5 10 15

def add(*args):
    total = 0
    for n in args:
        total += n
    return total
 
 
small_numbers = [1, 2, 3]
large_numbers = [9999999, 1111111]
 
print(add(*small_numbers))  # 6
print(add(*large_numbers))  # 11111110


def say_bye(**names):
    for name in names:
        print("Au revoir,", name)

    for key, value in names.items():
        print(f"{key}:{value}")
 
 
humans = {"Laura": {"age": 34, "fave_color": "purple"},
          "Robin": {"age": 28, "fave_color": "turquoise"}}
say_bye(**humans)

# Au revoir, Laura
# Au revoir, Robin
# Laura:{'age': 34, 'fave_color': 'purple'}
# Robin:{'age': 28, 'fave_color': 'turquoise'}

def concat(*args):
    return "".join(args)
print(concat("python"))      # python
print(concat("cat", "dog"))  # catdog

def create_function(n):
    return lambda x: n * x

# Creating a function that doubles its argument
doubler = create_function(2)
 
# This function will triple its argument
tripler = create_function(3)
 
doubler(2)
# Outputs 4
 
tripler(2)
# Outputs 6

-------------------------------
def func(x):
    if x % 2 == 0:
        return 'even'
    else:
        return 'odd'

func = (lambda x: 'even' if x % 2 == 0 else 'odd')

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