Python闭包技巧介绍

from urllib.request import urlopen
class UrlTemplate:
     def __init__(self, template) -> None:
         self.template = template
     def open(self, **kwargs):
         return urlopen(self.template.format_map(kwargs))
    
 yahoo = UrlTemplate('http://finance.yahoo.com/d/quotes.csv?s={names}&f={fields}')
 for line in yahoo.open(names='IBM,AAPL,FB', fields = 'sllclv'):
     print(line.decode('utf-8'))

def urltempalte(template):
    # 后面用对象再次调用函数的时候传入kwargs
    def opener(**kwargs):
        return urlopen(template.format_map(kwargs))
    return opener

yahoo = urltempalte('http://finance.yahoo.com/d/quotes.csv?s={names}&f={fields}')
for line in yahoo(names='IBM,AAPL,FB', fields = 'sllclv'):
    print(line.decode('utf-8'))

def sample():
    n = 0
    # 闭包函数
    def func():
        print("n =", n)
    
    # 存取函数(accessor function)，即getter/setter方法
    def get_n():
        return n

    def set_n(value):
        # 必须要加nolocal才能修改内层变量
        nonlocal n
        n = value

    # 做为函数属性附加
    func.get_n = get_n
    func.set_n = set_n
    return func

f = sample()
f() # n = 0
f.set_n(10)
f() # n = 10
print(f.get_n()) # 10

import sys
class ClosureInstance:
    def __init__(self, locals=None) -> None:
        if locals is None:
            locals = sys._getframe(1).f_locals 
            
        # Update instance dictionary with callables
        self.__dict__.update(
            (key, value) for key, value in locals.items() if callable(value)
        )

    # Redirect special methods
    def __len__(self):
        return self.__dict__['__len__']()
    
# Example use
def Stack():
    items = []

    def push(item):
        items.append(item)
    
    def pop():
        return items.pop()
    
    def __len__():
        return len(items)
    
    return ClosureInstance()

s = Stack()
print(s) # <__main__.ClosureInstance object at 0x101efc280>
s.push(10)
s.push(20)
s.push('Hello')
print(len(s)) # 3
print(s.pop()) # Hello
print(s.pop()) # 20
print(s.pop()) # 10

class Stack2:
    def __init__(self) -> None:
        self.items = []
    
    def push(self, item):
        self.items.append(item)

    def pop(self):
        return self.items.pop()
    
    def __len__(self):
        return len(self.items)

from timeit import timeit
s = Stack()
print(timeit('s.push(1);s.pop()', 'from __main__ import s'))
# 0.98746542
s = Stack2()
print(timeit('s.push(1);s.pop()', 'from __main__ import s'))
# 1.07070521