from __future__ import division
n=int(input("please input odd numer:"))
def getpi(n):
result=0
if n%2==0:
print("you 's number not odd")
exit(1)
sign=1
for i in range(1,n+1,2):
result+=sign*4/i
sign=sign*(-1)
return result
print(getpi(n))
用了for,回圈是啥意思?