作为Python的第一个练习,我试图编写一个使用循环来查找素数的程序。一切工作与for循环,所以我想使用一个while循环。这有效,但程序返回一些不正确的数字。用于查找素数的Python循环
import math
# looking for all primes below this number
max_num = int(input("max number?: "))
primes = [2] # start with 2
test_num = 3 # which means testing starts with 3
while test_num < max_num:
i = 0
# It's only necessary to check with the primes smaller than the square
# root of the test_num
while primes[i] < math.sqrt(test_num):
# using modulo to figure out if test_num is prime or not
if (test_num % primes[i]) == 0:
test_num += 1
break
else:
i += 1
else:
primes.append(test_num)
test_num += 1
print(primes)
因此,奇怪的是,为max_num=100
返回:
[2, 3, 5, 7, 9, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]
这是除了9,25和49,我想不通为什么正确的。
'primes [i] <= math.sqrt(test_num)' – vesche
您是否注意到数字是奇数? – njzk2
A'while ... else'!记得当它进入'else'后有乐趣(我不知道其他人,但我一直避免'while-else'和'for-else',并且从未在其他人的代码中看到过他们;他们感觉不直观) – dwanderson