如何使用Python找到立方根？
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How to find cube root using Python?
提问by Luke D
Here is how, this is the best way, I have found:
这是我发现的最佳方法：
x = int(raw_input("Enter an integer: "))
for ans in range(0, abs(x) + 1):
if ans ** 3 == abs(x):
break
if ans ** 3 != abs(x):
print x, 'is not a perfect cube!'
else:
if x < 0:
ans = -ans
print 'Cube root of ' + str(x) + ' is ' + str(ans)
Is there a better way, preferably one that avoids having to iterate over candidate values?
有没有更好的方法，最好是避免迭代候选值的方法？
回答by Bhargav Rao
The best way is to use simple math
最好的方法是使用简单的数学
>>> a = 8
>>> a**(1./3.)
2.0
EDIT
编辑
For Negative numbers
对于负数
>>> a = -8
>>> -(-a)**(1./3.)
-2.0
Complete Program for all the requirements as specified
完成指定的所有要求的程序
x = int(input("Enter an integer: "))
if x>0:
ans = x**(1./3.)
if ans ** 3 != abs(x):
print x, 'is not a perfect cube!'
else:
ans = -((-x)**(1./3.))
if ans ** 3 != -abs(x):
print x, 'is not a perfect cube!'
print 'Cube root of ' + str(x) + ' is ' + str(ans)
回答by NPE
You could use x ** (1. / 3)to compute the (floating-point) cube root of x.
您可以x ** (1. / 3)用来计算 的（浮点）立方根x。
The slight subtlety here is that this works differently for negative numbers in Python 2 and 3. The following code, however, handles that:
这里的微妙之处在于，对于 Python 2 和 3 中的负数，它的工作方式不同。 但是，以下代码处理了这个问题：
def is_perfect_cube(x):
x = abs(x)
return int(round(x ** (1. / 3))) ** 3 == x
print(is_perfect_cube(63))
print(is_perfect_cube(64))
print(is_perfect_cube(65))
print(is_perfect_cube(-63))
print(is_perfect_cube(-64))
print(is_perfect_cube(-65))
print(is_perfect_cube(2146689000)) # no other currently posted solution
# handles this correctly
This takes the cube root of x, rounds it to the nearest integer, raises to the third power, and finally checks whether the result equals x.
这取 的立方根x，将其四舍五入到最接近的整数，进行三次幂，最后检查结果是否等于x。
The reason to take the absolute value is to make the code work correctly for negative numbers across Python versions (Python 2 and 3 treat raising negative numbers to fractional powers differently).
取绝对值的原因是为了让代码在 Python 版本中正确处理负数（Python 2 和 3 将负数提升为分数幂的处理方式不同）。
回答by NPE
def cube(x):
if 0<=x: return x**(1./3.)
return -(-x)**(1./3.)
print (cube(8))
print (cube(-8))
Here is the full answer for both negative and positive numbers.
这是负数和正数的完整答案。
>>>
2.0
-2.0
>>>
Or here is a one-liner;
或者这里是单线；
root_cube = lambda x: x**(1./3.) if 0<=x else -(-x)**(1./3.)
