More Control Flow Tools

如果在循环当中对序列进行修改,不会报错,但是肯定会有各种各样的问题
建议: for循环的序列应该是原序列的copy,推荐用[:]来复制,这样易读性更佳

>>> for w in words[:]:  # Loop over a slice copy of the entire list.
...     if len(w) > 6:
...         words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']

py3中,range直接返回的就是迭代对象
循环语句当中也可以有else子句,用在循环迭代结束之后

>>> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 0:
...             print(n, 'equals', x, '*', n//x)
...             break
...     else:
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3

pass语句的用处
占位符,最小类,while true
for vs while
个人认为对象是个序列的时候用for
其他数据结构算法时while用的比较多
以可读性为准
如果一直执行到整个函数结束还没有碰到 return 语句，也返回 None。
函数的默认值只计算一次

i = 5
def f(arg=i):
    print(arg)
i = 6
f()

函数的默认值是个可变对象的时候,推荐这样写

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

关键字参数必须写在位置参数之后
(name必须出现在*name之前）
学会使用文档字符串

>>> def my_function():
...     """Do nothing, but document it.
...
...     No, really, it doesn't do anything.
...     """
...     pass
...
>>> print(my_function.__doc__)
Do nothing, but document it.

    No, really, it doesn't do anything.