python学习易错点1

1.>>> d = {'x': 'A', 'y': 'B', 'z': 'C' }
>>> for k, v in d.iteritems():
...     print k, '=', v
... 
y = B
x = A
z = C

2.>>> L = ['Hello', 'World', 'IBM', 'Apple']
>>> [s.lower() for s in L]
['hello', 'world', 'ibm', 'apple']


3.

def add(x, y, f):
    return f(x) + f(y)

当我们调用add(-5, 6, abs)时，参数x，y和f分别接收-5，6和abs，根据函数定义，我们可以推导计算过程为：

x ==> -5
y ==> 6
f ==> abs
f(x) + f(y) ==> abs(-5) + abs(6) ==> 11

用代码验证一下：

>>> add(-5, 6, abs)
11