python入门08_python_interview_question学习笔记

str1 = "k:1|k1:2|k2:3|k3:4"
def str2dict(str1):
    dict1 = {}
    for iterms in str1.split('|'):
        key,value = iterms.split(':')
        dict1[key] = value
    return dict1
#字典推导式
d = {k:int(v) for t in str1.split("|") for k, v in (t.split(":"), )}

def singleton(cls):
    instances = {}
    def wrapper(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    return wrapper
    
    
@singleton
class Foo(object):
    pass
foo1 = Foo()
foo2 = Foo()
print(foo1 is foo2)  # True

class Singleton(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, '_instance'):
            cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
        return cls._instance
    
    
class Foo(Singleton):
    pass

foo1 = Foo()
foo2 = Foo()

print(foo1 is foo2)  # True

class Singleton(type):
    def __call__(cls, *args, **kwargs):
        if not hasattr(cls, '_instance'):
            cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instance


# Python2
class Foo(object):
    __metaclass__ = Singleton

# Python3
class Foo(metaclass=Singleton):
    pass

foo1 = Foo()
foo2 = Foo()
print(foo1 is foo2)  # True

def atoi(s):
    num = 0
    for v in s:
        for j in range(10):
            if v == str(j):
                num = num * 10 + j
    return num

def atoi(s):
    num = 0
    for v in s:
        num = num * 10 + ord(v) - ord('0')
    return num

def atoi(s):
    num = 0
    for v in s:
        t = "%s * 1" % v
        n = eval(t)
        num = num * 10 + n
    return num

from functools import reduce
def atoi(s):
    return reduce(lambda num, v: num * 10 + ord(v) - ord('0'), s, 0)

reduce(lambda x,y : x*y,range(1,n+1))

def multipliers():
    return [lambda x: i *x for i in range(4)]
print([m(2) for m in multipliers()])

def multipliers():
    for i in range(4):
        yield lambda x: i *x
def multipliers():
    return [lambda x,i = i: i*x for i in range(4)]