从带有地图的类方法调用NumPy时发生Python错误 [英] Python error when calling NumPy from class method with map

问题描述

以下代码抛出错误:

Traceback (most recent call last):
  File "", line 25, in <module>
    sol = anna.main()
  File "", line 17, in main
    sol = list(map(self.eat, self.mice))
  File "", line 12, in eat
    calc = np.sqrt((food ** 5))
AttributeError: 'int' object has no attribute 'sqrt'

代码:

import numpy as np
#import time

class anaconda():

    def __init__(self):
        self.mice = range(10000)

    def eat(self, food):
        calc = np.sqrt((food ** 5))
        return calc

    def main(self):

        sol = list(map(self.eat, self.mice))
        return sol


if __name__ == '__main__':
    #start = time.time()
    anna = anaconda()
    sol = anna.main()
    print(len(sol))
    #print(time.time() - start)

我相信我犯了一个严重的错误，因为Python似乎将NumPy中的'np'解释为整数，但是我不知道为什么.

I believe I made a serious mistake, because it seems like Python interprets the 'np' from NumPy as an integer, but I have no glimpse why that is.

推荐答案

我将尝试为已经给出的答案添加精确答案. numpy.sqrt有一些math.sqrt没有的限制.

I'll try to add a precise answer to those that have already been given. numpy.sqrt has some limitations that math.sqrt doesn't have.

import math
import numpy  # version 1.13.3

print(math.sqrt(2 ** 64 - 1))
print(numpy.sqrt(2 ** 64 - 1))

print(math.sqrt(2 ** 64))
print(numpy.sqrt(2 ** 64))

返回(使用Python 3.5):

returns (with Python 3.5) :

4294967296.0
4294967296.0
4294967296.0
Traceback (most recent call last):
  File "main.py", line 8, in <module>
    print(numpy.sqrt(2 ** 64))
AttributeError: 'int' object has no attribute 'sqrt'

实际上，2 ** 64等于18,446,744,073,709,551,616，并且根据C数据类型(版本C99)的标准，long long unsigned integer类型至少包含0和18,446,744,073,709,551,615之间的范围.

In fact, 2 ** 64 is equal to 18,446,744,073,709,551,616 and, according to the standard of C data types (version C99), the long long unsigned integer type contains at least the range between 0 and 18,446,744,073,709,551,615 included.

出现AttributeError的原因是，numpy看到了一个不知道如何处理的类型(转换为C数据类型后)，默认情况下是在对象上调用sqrt方法(但是不会) t存在).如果我们使用浮点数而不是整数，那么所有内容都将使用numpy:

The AttributeError occurs because numpy, seeing a type that it doesn't know how to handle (after conversion to C data type), defaults to calling the sqrt method on the object (but that doesn't exist). If we use floats instead of integers then everything will work using numpy:

import numpy  # version 1.13.3

print(numpy.sqrt(float(2 ** 64)))

返回:

4294967296.0

因此，也可以在代码中将calc = np.sqrt(food ** 5)替换为calc = np.sqrt(float(food ** 5))，而不是用math.sqrt替换numpy.sqrt.

So instead of replacing numpy.sqrt by math.sqrt, you can alternatively replace calc = np.sqrt(food ** 5) by calc = np.sqrt(float(food ** 5)) in your code.

我希望这个错误现在对您更有意义.

I hope this error will make more sense to you now.

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