"for L in item"循环中的语法无效

Question

我有一种感觉,我错过了一些非常简单的东西,但在这一个功能中:

def triplets(perimeter):

    triplets, n, a, b, c = 0  #number of triplets, a, b, c, sides of a triangle, n is used to calculate a triple
    L = primes(int(math.sqrt(perimeter)) #list of primes to divide the perimeter

    for item in L: #iterate through the list of primes
        if perimeter % item == 0: #check if a prime divides the perimeter
            n = perimeter / item
            a = n**2 - (n+1)**2 #http://en.wikipedia.org/wiki/Pythagorean_triple
            b = 2n*(n+1)
            c = n**2 + n**2
            if a+b+c == perimeter: #check if it adds up to the perimeter of the triangle
                triplets = triplets + 1

    return triplets

我收到错误:

    for item in L:
                 ^
SyntaxError: invalid syntax

为了完整性,我的整个程序看起来像这样:

import math

def primes(n): #get a list of primes below a number
    if n==2: return [2]
    elif n<2: return []
    s=range(3,n+1,2)
    mroot = n ** 0.5
    half=(n+1)/2-1
    i=0
    m=3
    while m <= mroot:
        if s[i]:
            j=(m*m-3)/2
            s[j]=0
            while j<half:
                s[j]=0
                j+=m
        i=i+1
        m=2*i+3
    return [2]+[x for x in s if x]

def triplets(perimeter):

    triplets, n, a, b, c = 0  #number of triplets, a, b, c, sides of a triangle, n is used to calculate a triple
    L = primes(int(math.sqrt(perimeter)) #list of primes to divide the perimeter

    for item in L: #iterate through the list of primes
        if perimeter % item == 0: #check if a prime divides the perimeter
            n = perimeter / item
            a = n**2 - (n+1)**2 #http://en.wikipedia.org/wiki/Pythagorean_triple
            b = 2n*(n+1)
            c = n**2 + n**2
            if a+b+c == perimeter: #check if it adds up to the perimeter of the triangle
                triplets = triplets + 1

    return triplets

def solve():
    best = 0
    perimeter = 0
    for i in range(1, 1000):
        if triplets(i) > best:
            best = triplets(i)
            perimeter = i
    return perimeter

print solve()

我使用的是Python 2.7.1.我在for循环后有一个分号,该primes(n)函数有效,我感觉它可能是一些愚蠢但我无法弄清楚是什么导致这种无效的语法.

Answer 1

您之前缺少一个右括号:

      L = primes(int(math.sqrt(perimeter)) #list of primes to divide the perimeter
#                ^   ^         ^         ^^
#nesting count   1   2         3         21

看看我们如何在线下方的"嵌套计数"中达不到0？