Python 内置函数 filter map reduce

 

def is_prime_num(num):
    if num <=3:
        return False
    for n in xrange(2, num):
        if num%n == 0:
            return False
    return True
# 找出1到100的素数
a = range(1, 100) 
f = filter(is_prime_num, a)
print f

 

 

# filter内建函数的python实现
def filter(bool_func,seq):
	filtered_seq = []
	for eachItem in seq:
		if bool_func(eachItem):
			filtered_seq.append(eachItem)
	return filtered_seq

 

 

>>> map(lambda x : None,[1,2,3,4])
[None, None, None, None]
>>> map(lambda x : x * 2,[1,2,3,4])
[2, 4, 6, 8]
>>> map(lambda x : x * 2,[1,2,3,4,[5,6,7]])
[2, 4, 6, 8, [5, 6, 7, 5, 6, 7]]
>>> map(lambda x : None,[1,2,3,4])
[None, None, None, None]


#  map内建函数的python实现：
def map(func,seq):
	mapped_seq = []
	for eachItem in seq:
		mapped_seq.append(func(eachItem))
	return mapped_seq

 

 

 

>>> reduce(lambda x,y : x + y,[1,2,3,4])
10
>>> reduce(lambda x,y : x + y,[1,2,3,4],10)
20

#  reduce的python实现： 
def reduce(bin_func,seq,initial=None):
	lseq = list(seq)
	if initial is None:
		res = lseq.pop(0)
	else:
		res = initial
	for eachItem in lseq:
		res = bin_func(res,eachItem)
	return res