此函数应该可以计算出阶乘，但不能。 [蟒-3.X]

Question

(Full disclosure, I am going through the Python tutorial at CodeAcademy, and am using their web-based IDE.)

def factorial(x):
    bang = 1
        for num in x:
            bang = bang * num
    return bang

In java, this works to generate a factorial from a number smaller than 2,147,483,647. I think it should work in python, but it doesn't. Instead I get the error:

"Traceback (most recent call last): File "python", line 3, in factorial TypeError: 'int' object is not iterable"

Perhaps there's something I'm not understanding here, or perhaps my syntax is wrong. I tested further and created a separate function called factorial that iterates:

def factorial(x):
    if x > 2:
        return x
    else:
        return x(factorial(x-1))

This also doesn't work, giving me the error:

"Traceback (most recent call last): File "python", line 11, in factorial TypeError: 'int' object is not callable"

I am a python noob, but it seems that both of these should work. Please advise on the best way to learn Python syntax...

Answer 1

You can't do for num in x if x is an integer. An integer isn't "iterable" as the error says. You want something like this:

def factorial(x):
    bang = 1
    for num in xrange(1, x+1):
        bang = bang * num
    return bang

The xrange (or range ) will generate the necessary range of numbers for the in to operate upon.

Answer 2

def f(x):
        if x < 2:
            return 1
        else:
            return x * f(x - 1)