文章目录
- 1. 函数对象
- 2. 高阶函数
- 3. 匿名函数
- 4. 可调用函数
- 5. 定位参数、仅限关键字参数
- 6. 获取参数信息
- 7. 函数注解
- 8. 支持函数式编程的包
1. 函数对象
代码语言：javascript
复制def factorial(n):
'''
returns n! n的阶乘
'''
return 1 if n < 2 else n * factorial(n - 1)
print(factorial(42))
print(factorial.__doc__) # returns n! n的阶乘
print(type(factorial)) # <class 'function'>
fact = factorial
print(fact) # <function factorial at 0x0000021512868EA0>
print(fact(4)) # 24
print(list(map(factorial, range(11))))
# [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800]
2. 高阶函数
代码语言：javascript
复制fruits = ['strawberry', 'fig', 'apple', 'cherry', 'raspberry', 'banana']
print(sorted(fruits, key=len)) # 按长度排序
# ['fig', 'apple', 'cherry', 'banana', 'raspberry', 'strawberry']
def reveres(word):
return word[::-1]
print(reveres("michael")) # leahcim
print(sorted(fruits, key=reveres)) # 逆序字符串排序
# ['banana', 'apple', 'fig', 'raspberry', 'strawberry', 'cherry']
3. 匿名函数
代码语言：javascript
复制print(sorted(fruits, key=lambda w : w[::-1]))
# ['banana', 'apple', 'fig', 'raspberry', 'strawberry', 'cherry']
4. 可调用函数
代码语言：javascript
复制print([callable(obj) for obj in (abs, str, 13, factorial)]) # [True, True, False, True]
代码语言：javascript
复制import random
class BingoCage:
def __init__(self, items):
self._items = list(items)
random.shuffle(self._items)
def pick(self):
try:
return self._items.pop()
except IndexError:
raise LookupError("pick from empty BingoCage")
def __call__(self):
return self.pick()
arr = [1, 2, 3, 4, 5]
bc = BingoCage(arr);
print(bc._items) # [1, 4, 3, 5, 2]
print(bc.pick()) # 2
print(bc._items) # [1, 4, 3, 5]
print(bc()) # 5, bc 实现了 __call_() 可调用
print(bc._items) # [1, 4, 3]
print(callable(bc)) # True
5. 定位参数、仅限关键字参数
代码语言：javascript
复制def tag(name, *content, cls=None, **attrs):
"""生成一个或多个HTML标签"""
if cls is not None:
attrs['class'] = cls
if attrs:
attr_str = ''.join(' %s="%s"' % (attr, value)
for attr, value
in sorted(attrs.items()))
else:
attr_str = ''
if content:
return 'n'.join('<%s%s>%s</%s>' %
(name, attr_str, c, name) for c in content)
else:
return '<%s%s />' % (name, attr_str)
print(tag('br')) # <br />
print(tag('p', 'hello')) # <p>hello</p>
print(tag('p', 'hello', 'world'))
# 第一个参数后的任意个 参数 被 *content 捕获，存入元组
# <p>hello</p>
# <p>world</p>
print(tag('p', 'hello', id=33, pid=24))
# 没有明确指定名称的关键字参数被 **attrs 捕获，存入字典
# <p id="33" pid="24">hello</p>
print(tag('p', 'hello', 'world', id=33, cls='sidebar', pid=24))
# cls 参数只能作为关键字参数
# <p class="sidebar" id="33" pid="24">hello</p>
# <p class="sidebar" id="33" pid="24">world</p>
print(tag(cont='testing', name="img"))
# <img cont="testing" />
my_tag = {'name': 'img', 'title': 'Sunset Boulevard',
'src': 'sunset.jpg', 'cls': 'framed'}
print(tag(**my_tag))
# ** 字典中所有元素作为单个参数传入，同名键绑定到对应具名参数，余下被 **attrs 捕获
# <img class="framed" src="sunset.jpg" title="Sunset Boulevard" />
代码语言：javascript
复制def f(a, *c, b):
return a, b
print(f(1, b=2)) # (1, 2)
print(f(1, 2, b=3)) # (1, 3) b= 必须写，因为前面有 * 参数
# print(f(1, 2)) # f() takes 1 positional argument but 2 were given
def f1(a, b, *c):
return a, b
print(f1(1, b=2)) # (1, 2)
print(f1(1, 2)) # (1, 2)
print(f1(1, 2, 3)) # (1, 2)
6. 获取参数信息
代码语言：javascript
复制from inspect import signature
sig = signature(tag)
print(sig) # (name, *content, cls=None, **attrs)
my_tag = {'name': 'img', 'title': 'Sunset Boulevard',
'src': 'sunset.jpg', 'cls': 'framed'}
bound_args = sig.bind(**my_tag)
print(bound_args)
# <BoundArguments (name='img', cls='framed', attrs={'title': 'Sunset Boulevard', 'src': 'sunset.jpg'})>
del my_tag['name']
bound_args = sig.bind(**my_tag)
# TypeError: missing a required argument: 'name'
7. 函数注解
代码语言：javascript
复制def clip(text: str, max_len: 'int > 0' = 80) -> str:
pass
print(clip.__annotations__) # 一个字典
# 注解可以是 类 或者 字符串
# {'text': <class 'str'>, 'max_len': 'int > 0', 'return': <class 'str'>}
sig = signature(clip)
print(sig) # (text: str, max_len: 'int > 0' = 80) -> str
print(sig.return_annotation) # <class 'str'>
for param in sig.parameters.values():
print(param.name, " ", param.annotation, " ", param.default)
# text <class 'str'> <class 'inspect._empty'>
# max_len int > 0 80
8. 支持函数式编程的包
代码语言：javascript
复制from functools import reduce
def fact(n):
return reduce(lambda a, b: a * b, range(1, n 1))
print(fact(5))
from operator import mul
def fact1(n):
return reduce(mul, range(1, n 1))
print(fact1(5))
代码语言：javascript
复制metro_data = [
('Tokyo', 'JP', 36.933, (35.689722, 139.691667)),
('Delhi NCR', 'IN', 21.935, (28.613889, 77.208889)),
('Mexico City', 'MX', 20.142, (19.433333, -99.133333)),
('New York-Newark', 'US', 20.104, (40.808611, -74.020386)),
('Sao Paulo', 'BR', 19.649, (-23.547778, -46.635833)),
]
from operator import itemgetter
import operator
for city in sorted(metro_data, key=itemgetter(1)):
print(city) # 按照 索引 1 排序
cc_name = itemgetter(1, 0)
for city in metro_data:
print(cc_name(city))
# ('JP', 'Tokyo')
# ('IN', 'Delhi NCR')
# ('MX', 'Mexico City')
# ('US', 'New York-Newark')
# ('BR', 'Sao Paulo')
print([name for name in dir(operator) if not name.startswith('_')])
# ['abs', 'add', 'and_', 'attrgetter', 'concat', 'contains', 'countOf',
# 'delitem', 'eq', 'floordiv', 'ge', 'getitem', 'gt', 'iadd', 'iand',
# 'iconcat', 'ifloordiv', 'ilshift', 'imatmul', 'imod', 'imul', 'index',
# 'indexOf', 'inv', 'invert', 'ior', 'ipow', 'irshift', 'is_', 'is_not',
# 'isub', 'itemgetter', 'itruediv', 'ixor', 'le', 'length_hint', 'lshift',
# 'lt', 'matmul', 'methodcaller', 'mod', 'mul', 'ne', 'neg', 'not_', 'or_',
# 'pos', 'pow', 'rshift', 'setitem', 'sub', 'truediv', 'truth', 'xor']
代码语言：javascript
复制from operator import methodcaller
s = 'the time has come'
upcase = methodcaller('upper') # 调用指定的方法 'upper'
print(upcase(s)) # THE TIME HAS COME
connect = methodcaller('replace', ' ', '-')
print(connect(s)) # the-time-has-come
代码语言：javascript
复制from operator import mul
from functools import partial
triple = partial(mul, 3)
print(triple(7)) # 21
print(list(map(triple, range(1, 10))))
# [3, 6, 9, 12, 15, 18, 21, 24, 27]
