开发笔记:python一等函数

def factorial(n):
‘‘‘returns n!‘‘‘
return 1 if n <2 else n * factorial(n - 1)
print(factorial(5)) #调用
print(help(factorial)) #打印__doc__属性
print(type(factorial)) #打印类型
#结果
120
Help on function factorial in module __main__:
factorial(n)
returns n! #__doc__属性
None
<class ‘function‘> #说明factorial是function类的一个实例

#创建一个函数，只有函数在调用的时候才会运行
def factorial(n):
‘‘‘returns n!‘‘‘
return 1 if n <2 else n * factorial(n-1)
fact = factorial
print(fact)
map_fact = map(factorial, range(11))
print(‘map fact:‘, map_fact)
print(list(map_fact))
#结果

map fact:

>>> def reverse(word):
... return word[::-1]
...
>>> reverse(‘testing‘)
‘gnitset‘
>>> reverse(fruits)
[‘banana‘, ‘raspberry‘, ‘cherry‘, ‘apple‘, ‘fig‘, ‘strawberry‘]
>>> fruits
[‘strawberry‘, ‘fig‘, ‘apple‘, ‘cherry‘, ‘raspberry‘, ‘banana‘]
>>> sorted(fruits, key=reverse)　　　　#reverse作为sorted函数的参数
[‘banana‘, ‘apple‘, ‘fig‘, ‘raspberry‘, ‘strawberry‘, ‘cherry‘]

>>>def factorial(n):
return 1 if n <2 else n * factorial(n - 1)
>>>list(map(factorial,range(6))) #0到5的阶乘
[1, 1, 2, 6, 24, 120]
list(map(factorial,filter(lambda n: n % 2,range(6)))) #过滤掉偶数的阶乘
[1, 6, 120]

from functools import reduce #reduce在functools模块下
from operator import add
reduce(add,range(100))
4950
sum(range(100))
4950

fruits = [‘banana‘, ‘raspberry‘, ‘cherry‘, ‘apple‘, ‘fig‘, ‘strawberry‘]
sorted(fruits, key=lambda word: word[::-1]) #逆置的单词排序，代替了sorted示例中的reverse函数
[‘banana‘, ‘apple‘, ‘fig‘, ‘raspberry‘, ‘strawberry‘, ‘cherry‘]

>>>[callable(obj) for obj in (abs,str,13)]
[True, True, False]

import random
class BingoCage:
def __init__(self, items):
self._items = list(items)
random.shuffle(self._items) #打乱顺序
def pick(self):
try:
return self._items.pop()
except IndexError:
raise LookupError(‘pick from empty BingoCage‘)
def __call__(self, *args, **kwargs): #实现__call__方法
return self.pick()
bingo = BingoCage(range(3))
print(bingo.pick())
print(bingo()) #调用bingo
print(callable(bingo)) #判断是否可调用
#结果：
0
2
True

>>>dir(factorial)
[‘__annotations__‘, ‘__call__‘, ‘__class__‘, ‘__closure__‘, ‘__code__‘, ‘__defaults__‘, ‘__delattr__‘, ‘__dict__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__get__‘, ‘__getattribute__‘, ‘__globals__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__kwdefaults__‘, ‘__le__‘, ‘__lt__‘, ‘__module__‘, ‘__name__‘, ‘__ne__‘, ‘__new__‘, ‘__qualname__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘]

def clip(text, max_len=20):
"""在max_len前面或后面的第一个空格处截断文本
"""
end = None
if len(text) > max_len:
space_before = text.rfind(‘ ‘, 0, max_len)
if space_before >= 0:
end = space_before
else:
space_after = text.rfind(‘ ‘, max_len)
if space_after >=0:
end = space_after
if end is None:
end = len(text)
return text[:end].rstrip()
print(clip.__defaults__) #从后往前扫描，故max_len的默认值为20
print(clip.__code__)
print(clip.__code__.co_argcount) #包含局部变量
print(clip.__code__.co_varnames) #如结果，实际参数为2

(20,)
"C:/py_code/nov06/Schimidt.py", line 1>
2
(‘text‘, ‘max_len‘, ‘end‘, ‘space_before‘, ‘space_after‘)