python高级特性和高阶函数及使用详解

# 处理字符串
str_lst = ['$1.123', ' $1123.454', '$899.12312']
def remove_space(str):
  """
  remove space
  """
  str_no_space = str.replace(' ', '')
  return str_no_space
def remove_dollar(str):
  """
  remove $
  """
  if '$' in str:
    return str.replace('$', '')
  else:
    return str
def clean_str_lst(str_lst, operations):
  """
    clean string list
  """
  result = []
  for item in str_lst:
    for op in operations:
      item = op(item)
    result.append(item)
  return result
clean_operations = [remove_space, remove_dollar]
result = clean_str_lst(str_lst, clean_operations)
print result

lst = [a1, a2 ,a3, ......, an]
　　reduce(func(x,y), lst) = func(func(func(a1, a2), a3), ......, an)

>>> def f(x):
...   return x + x
...
>>> r = map(f, [1, 2, 3, 4, 5, 6, 7, 8, 9])
>>> list(r)
[2, 4, 6, 8, 10, 12, 14, 16, 18]
# 提供了两个列表，对相同位置的列表数据进行相加
>>> map(lambda x, y: x + y, [1, 3, 5, 7, 9], [2, 4, 6, 8, 10])
[3, 7, 11, 15, 19]

>>> from functools import reduce
>>> def add(x, y):
...   return x + y
...
>>> reduce(add, [1, 3, 5, 7, 9])
25
>>> reduce(lambda x, y: x+y, [1,2,3,4,5]) # 使用 lambda 匿名函数
15
from functools import reduce
def add(x,y):
  return x + y
print (reduce(add, range(1, 101)))

def is_odd(n):
  return n % 2 == 1
list(filter(is_odd, [1, 2, 4, 5, 6, 9, 10, 15]))
# 结果: [1, 5, 9, 15]
def not_empty(s):
  return s and s.strip()
list(filter(not_empty, ['A', '', 'B', None, 'C', ' ']))
# 结果: ['A', 'B', 'C']

>>>a = [5,7,6,3,4,1,2]
>>> b = sorted(a)    # 保留原列表
>>> a 
[5, 7, 6, 3, 4, 1, 2]
>>> b
[1, 2, 3, 4, 5, 6, 7]
此外，sorted()函数也是一个高阶函数，它还可以接收一个key函数来实现自定义的排序，例如按绝对值大小排序：
>>> sorted([36, 5, -12, 9, -21], key=abs)
#key指定的函数将作用于list的每一个元素上，并根据key函数返回的结果进行排序。对比原始的list和经过key=abs处理过的list：
#list = [36, 5, -12, 9, -21]
#keys = [36, 5, 12, 9, 21]
[5, 9, -12, -21, 36]
#字符串排序
>>> sorted(['bob', 'about', 'Zoo', 'Credit'])
['Credit', 'Zoo', 'about', 'bob']

>>> sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower, reverse=True)
['Zoo', 'Credit', 'bob', 'about']

>>>a = raw_input("input:")
input:123
>>> type(a)
<type 'str'>       # 字符串
>>> a = raw_input("input:")
input:runoob
>>> type(a)
<type 'str'>       # 字符串
>>>
input() 需要输入 python 表达式
>>>a = input("input:")
input:123         # 输入整数
>>> type(a)
<type 'int'>        # 整型
>>> a = input("input:")  
input:"runoob"      # 正确，字符串表达式
>>> type(a)
<type 'str'>       # 字符串
>>> a = input("input:")
input:runoob        # 报错，不是表达式
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "<string>", line 1, in <module>
NameError: name 'runoob' is not defined
<type 'str'>