Python 内置函数 filter map reduce

liukun2009

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