1.Map函数 - 列表解析
①.map()函数解析
(1).python源码信息
C:\Users\ArSang>python
Python3.6.3rc1 (v3.6.3rc1:d8c174a, Sep 19 2017, 16:39:51) [MSC v.1900 64bit (AMD64)] on win32
Type"help", "copyright", "credits" or "license" formore information.>>>help(map)
Help on class mapinmodule builtins:
class map(object)| map(func, *iterables) -->map object|
| Make an iterator that computes the functionusing arguments from|each of the iterables. Stops when the shortest iterable is exhausted.|
|Methods defined here:|
| __getattribute__(self, name, /)| Returngetattr(self, name).|
| __iter__(self, /)|Implement iter(self).|
| __new__(*args, **kwargs) from builtins.type| Create and return a new object. See help(type) foraccurate signature.|
| __next__(self, /)|Implement next(self).|
|__reduce__(...)| Return state information for pickling.
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(2).map()接收一个函数和一个可迭代对象list数组，并通过函数方法去迭代list中的每个元素从而得到并返回一个新的list
p_list = [1, 2, 3, 4]#构建函数
deff(x):"""实现给list中的每个元素+2
:return:"""
return x + 2
'''3.x中返回需要添加返回类型，spe=list()，2.x中不需要，在3.0中map函数仅仅是创建一个待运行的命令容器，只有其他函数调用他的时候才会返回结果
Python 2.x 返回列表 Python 3.x 返回迭代器'''spe=list(map(f, p_list))print(spe) #返回新的list
print(id(p_list)) #查询原数组内存地址
print(id(spe)) #查询新数组内存地址
"""spe≠p_list"""
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(3).使用for循环迭代实现
l = [1, 2, 3, 4]defadd_list(x):return x + 2
defmap_list(f, arr_list):
temp=[]for i inarr_list:
rep=f(i)
temp.append(rep)returntemp
res=map_list(add_list, l)print(res) #返回新的数组
print(id(l)) #查询原数组内存地址
print(id(res)) #查询新数组非常地址
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(4).列表解析for与map
'''Python下：for效率 < map()效率'''
②.map()函数也可接受多参数的函数
l = [1, 2, 3, 4]#将l列表加2后返回一个新列表
rep = map(lambda x: x + 2, l)print(list(rep))
a= [1, 2, 3, 4]
b= [5, 6, 7, 8]#将a,b两个数组中的元素相乘，返回一个新的列表元素
ret_list = map(lambda x, y: x *y, a, b)print(list(ret_list))
③普遍函数与匿名方法：
a = [1, 2, 3, 4]
b= [5, 6, 7, 8]defadd_fun(number1, number2):
number1+=number2returnnumber1defsum_list():#普遍函数
res1 =map(add_fun, a, b)#匿名函数
res2 = map(lambda x: x ** 2, [x for x in range(10)])print(list(res1), list(res2))if __name__ == '__main__':
sum_list()
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④其他应用
a = ['YSDSASD', 'lsfrr', 'tGdDSd', 'Sdddd']deffun(f):"""将列表的第一个字母偶同意大写，后面的字母统一小写
:return:"""
return f[0:1].upper() + f[1:].lower()if __name__ == '__main__':
lit=map(fun, a)print(list(lit))
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2.reduce()函数 - 递归计算
①reduce()函数解析
(1).python3中源码解析
from functools importreduceprint(help(reduce))
reduce(...)
reduce(function, sequence[, initial])->value
Apply a function of two arguments cumulatively to the items of a sequence,fromleft to right, so as to reduce the sequence to a single value.
For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
((((1+2)+3)+4)+5). If initial is present, it isplaced before the items
of the sequencein the calculation, andserves as a default when the
sequenceis empty.
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(2).reduce()函数取值规则：
#python3中使用reduce需要导入
from functools importreduce
a= [1, 2, 3, 4]
app_list= reduce(lambda x, y: x *y, a)
num_list= reduce(lambda x, y: x * y, range(1, 5))print(app_list)print(num_list)'''a = [1, 2, 3, 4]
第一次相乘：x([0])*y([1])
第二次相乘：x(([0]*[1])result)*y([2])
第三次相乘：x(([0]*[1]*[2])result)*y([3])
.....'''
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②其他应用
#python3中使用reduce需要导入
from functools importreduce
a= [1, 2, 3]'''x * y的单结果+1
第一次计算：1 *2 + 1 = result
第二次计算：（result*3）+1 = resulttwo
第三次计算：（resulttwo*4）+1
....'''app_list= reduce(lambda x, y: x * y+1, a)#第三参数：5 x*y的总结果*5
num_list = reduce(lambda x, y: x * y, range(1, 5), 5)print(app_list)print(num_list)
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3.filter()函数 - 过滤器
①filter()函数解析
(1).python源码解析
C:\Users\ArSang>python
Python3.6.3rc1 (v3.6.3rc1:d8c174a, Sep 19 2017, 16:39:51) [MSC v.1900 64bit (AMD64)] on win32
Type"help", "copyright", "credits" or "license" formore information.>>>help(filter)
Help onclass filter inmodule builtins:classfilter(object)| filter(function or None, iterable) -->filter object|
| Return an iterator yielding those items of iterable forwhich function(item)| is true. If function is None, returnthe items that are true.|
|Methods defined here:|
| __getattribute__(self, name, /)|Return getattr(self, name).|
| __iter__(self, /)|Implement iter(self).|
| __new__(*args, **kwargs) frombuiltins.type| Create and return a new object. See help(type) foraccurate signature.|
| __next__(self, /)|Implement next(self).|
| __reduce__(...)| Return state information for pickling.
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②filter()返回值
#列表解析的方式
b = [i for i in range(10) if i > 5 and i < 8]print(list(b))#filter()函数方式
b = filter(lambda x: x > 5 and x < 8, range(10))print(list(b))'''1.filter()函数首先需要返回一个bool类型的函数
2.如上示例，判断x是否大于5且小于8，最后将这个函数作用到range(10)的每个函数中，如果为True，则将满足条件的元素组成一个列表返回'''
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③其他应用
（1）.删除None列表元素
defis_empty(s):"""删除None元素字符
:return:"""
return s and len(s.strip()) >0if __name__ == '__main__':
b= ['', 'str', ' ', 'end', '', '']print(list(filter(is_empty, b)))
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（2）.匿名函数和自定义函数
importrandom#自定义函数
'''def fun(x):
return x * 2
arr_list = []
for i in range(10):
arr_list.append(random.randint(1, 20))
print(arr_list)
if __name__ == '__main__':
print(list(filter(fun, arr_list)))'''
#匿名函数
arr_lst =[]for i in range(10):
arr_lst.append(random.randint(1, 20))print(arr_lst)if __name__ == '__main__':print(list(filter(lambda x: x * 2, arr_lst)))
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