中给出的大多数数字的意外输出。（Python）

我正在尝试用Python编写一个素因子分解代码，以下是我到目前为止所做的工作：

# Prime Factorisation
while True:
    try:
        n, primes, factorisation, dividers, factors = abs(int(input('Enter an integer to find it\'s Prime Factorisation: '))), [], [], [], [] # Asks for input and assigns multiple variables and lists
        break
    except:
        print('Please enter an integer.')
def isprime(num): # Checks if given number is prime
    for i in range(1,num+1):
        if num % i == 0:
            factors.append(i)
    return len(factors)== 2
for i in range(2,n+1):
    if isprime(i):
        primes.append(i)
for i in primes: # This code does the actual Prime Factorisation
    while n % i == 0: # If n (The input the user gave) is divisible by i of list primes: 
        factorisation.append(n) # n is added to factorisation
        dividers.append(i) # i is added to divisors
        n /= i  # n = n / i
output = str(dividers).replace(', ',' x ').replace('[','').replace(']','') # Pretties up the list dividers
print(str(factorisation[0]) + ' = ' + output) # Prints given value and divisors

---

该代码适用于256这样的数字，但与其他数字的输出很奇怪，请帮我找出错误，谢谢

函数isprime中的局部变量因子缺失：

def isprime(num): # Checks if given number is prime
    factors = []
    for i in range(1,num+1):
        if num % i == 0:
            factors.append(i)
    return len(factors)== 2

工作正常，经过此校正后

工作示例（问题在于共享的“因子”列表变量）

输出

# > python test.py
Enter an integer to find it's Prime Factorisation: 247
247 = 13 x 19

清洁版 只是源代码的一个更干净的版本

# Prime Factorisation
while True:
    try:
        n = abs(int(input(
            'Enter an integer to find it\'s Prime Factorisation: ')))  # Asks for input and assigns multiple variables and lists
        break
    except:
        print('Please enter an integer.')


def isprime(num):  # Checks if given number is prime
    return len([n for n in range(1, num + 1) if num % n == 0]) == 2


primes = [n for n in range(2, n + 1) if isprime(n)]

factorisation, dividers = [], []
for i in primes:  # This code does the actual Prime Factorisation
    while n % i == 0:  # If n (The input the user gave) is divisible by i of list primes:
        factorisation.append(n)  # n is added to factorisation
        dividers.append(i)  # i is added to divisors
        n /= i  # n = n / i

output = str(dividers).replace(', ', ' x ').replace('[', '').replace(']', '')  # Pretties up the list dividers

print(str(factorisation[0]) + ' = ' + output)  # Prints given value and divisors

---

此功能已中断：

...
factors = []
...

def isprime(num): # Checks if given number is prime
    for i in range(1,num+1):
        if num % i == 0:
            factors.append(i)
    return len(factors)== 2

因此，

isprime

将继续一次又一次地向全局变量

factors

追加

i

，即使它已经包含了这个数字。因此，

因子

的长度将继续增长，超过2。事实上，对于

n==255

，

因子将包含1456个数字！对于任何大于2的数字，函数将返回
False
，找到的唯一素数是2

您需要将
因子设置为本地：

def isprime(num): # Checks if given number is prime
    factors = []
    for i in range(1,num+1):
        if num % i == 0:
            factors.append(i)
    return len(factors) == 2

或使用生成器表达式以避免浪费内存：

def isprime(num):
    factors = (f for f in range(1, num + 1) if num % f == 0)

    assert next(factors) == 1 # this is always true

    try:
        # this will be true if there are no more factors other than `num` itself
        return next(factors) == num
    except StopIteration:
        # There are no more factors, so `num` must equal 1, which is not prime
        return False

“用其他数字给出奇怪的输出”-它们有什么奇怪之处？因子应该是isprime函数定义中的局部变量
def isprime(num):
    factors = (f for f in range(1, num + 1) if num % f == 0)

    assert next(factors) == 1 # this is always true

    try:
        # this will be true if there are no more factors other than `num` itself
        return next(factors) == num
    except StopIteration:
        # There are no more factors, so `num` must equal 1, which is not prime
        return False