python实现range函数

#!/usr/bin/env python

def r(start,end=None,step=1):
if step>0:
if not end:
start, end = 0, start
check = lambda x,y:x<y
elif step<0:
check = lambda x,y:x>y
else:
raise ValueError("range() step argument must not be zero")

tmp = []
while check(start, end):
tmp.append(start)
start+=step
return tmp

print r(2,6)
print r(1,10,2)
print r(10,-9,-4)
print r(-10)
print r(1,10,0)

$ python ran.py
[2, 3, 4, 5]
[1, 3, 5, 7, 9]
[10, 6, 2, -2, -6]
[]
Traceback (most recent call last):
File "ran.py", line 25, in <module>
print r(1,10,0)
File "ran.py", line 13, in r
raise ValueError("range() step argument must not be zero")
ValueError: range() step argument must not be zero