Python+Selenium学习笔记11

def f(a, L=[]):
    L.append(a)
    return L

print f(5)
print f(2)

输出

def f(a, L=None):
    if L is None:
        L = []
    L.append(a)
    return L

print f1(5)
print f1(2)

输出

 

 上面两个函数的区别，f()输出的结果是累加的，f1()输出的结果是独立的

If you don’t want the default to be shared between subsequent calls -> 用f1()

4.7.2. Keyword Arguments

def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
    print("-- This parrot wouldn't", action, end=' ')
    print("if you put", voltage, "volts through it.")
    print("-- Lovely plumage, the", type)
    print("-- It's", state, "!")

parrot(1000)                                          # 1 positional argument
parrot(voltage=1000)                                  # 1 keyword argument
parrot(voltage=1000000, action='VOOOOOM')             # 2 keyword arguments
parrot(action='VOOOOOM', voltage=1000000)             # 2 keyword arguments
parrot('a million', 'bereft of life', 'jump')         # 3 positional arguments
parrot('a thousand', state='pushing up the daisies')  # 1 positional, 1 keyword

# 异常情况，下面几种情况运行都不成功

parrot()                     # required argument missing ，必须有个必填参数
parrot(voltage=5.0, 'dead')  # non-keyword argument after a keyword argument ，这个当我把第二个参数换成status='dead'时运行成功。我的理解是前面参数用了参数名，后面就必须得跟，要是前面没跟，那后面跟不跟都可以
parrot(110, voltage=220)     # duplicate value for the same argument，重复传参
parrot(actor='John Cleese')  # unknown keyword argument #参数typo

 输出

解析

传值时，带变量voltage=1000，运行时会自动匹配到对应的位置

不带变量parrot('a million', 'bereft of life', 'jump') ，则按顺序传参

 定义函数有 *name和 **name时， *name 必须在 **name之前。

def cheeseshop(kind, *arguments, **keywords):
    print("-- Do you have any", kind, "?")
    print("-- I'm sorry, we're all out of", kind)
    for arg in arguments:
        print(arg)
    print("-" * 40)
    for kw in keywords:
        print(kw, ":", keywords[kw])

cheeseshop("Limburger", "It's very runny, sir.",
           "It's really very, VERY runny, sir.",
           shopkeeper="Michael Palin",
           client="John Cleese",
           sketch="Cheese Shop Sketch")

# 输出结果
-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
shopkeeper : Michael Palin
client : John Cleese
sketch : Cheese Shop Sketch