在 Python 中是什么导致了这个错误(AttributeError: 'Mul' object has no attribute 'cos')? [英] What causes this error (AttributeError: 'Mul' object has no attribute 'cos') in Python?

问题描述

我在 Python 中尝试计算定积分时收到以下错误代码.

I am getting the following error code when trying to evaluate a definite integral in Python.

AttributeError                            Traceback (most recent call last)
<ipython-input-7-2be8718c68ec> in <module>()
      7 x, n = symbols('x n')
      8 
----> 9 f = (cos(n*x))*(x**2-pi**2)^2
     10 integrate(f,(x,-n*pi,n*pi))
     11 

AttributeError: 'Mul' object has no attribute 'cos' 

我已在下面复制了我的输入代码.感谢您的帮助.

I have copied my input code below. Thanks for any help.

from pylab import *
from sympy import *
from numpy import *

init_printing(use_unicode=False, wrap_line=False, no_global=True)

x, n = symbols('x n')

f = (cos(n*x))*(x**2-pi**2)^2
integrate(f,(x,-n*pi,n*pi))

推荐答案

你的问题是命名空间冲突，在这里

Your problem is with namespace clash, here

from sympy import *
from numpy import *

因为 numpy 和 sympy 都有自己的 cos 定义.该错误告诉您 Mul 对象(即 n*x)没有余弦方法，因为解释器现在在 sympy 和 numpy 方法.改为这样做

Since both numpy and and sympy have their own definition of cos. The error is telling you that the Mul object (which is n*x) does not have a cosine method, since the interpreter is now confused between the sympy and numpy methods. Do this instead

import pylab as pl
import numpy as np
import sympy as sp

x, n = sp.symbols('x n')
f = (sp.cos(n*x))*(x**2-sp.pi**2)**2
sp.integrate(f,(x,-n*sp.pi,n*sp.pi))

另请注意，我已将 ^ 更改为 ** 因为 ^ 是 Not 运算符在 >同情.在这里，我假设您需要来自 sympy.core.numbers.Pi 的符号 Pi 而不是来自 numpy 的数字.如果你想要后者，那么就这样做

Also note that I have changed ^ to ** as ^ is the Not operator in sympy. Here, I am assuming that you need the symbolic Pi from sympy.core.numbers.Pi and not the numeric one from numpy. If you want the latter, then do this

f = (sp.cos(n*x))*(x**2-np.pi**2)**2
sp.integrate(f,(x,-n*np.pi,n*np.pi))

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