TypeError:无法将表达式转换为float

Question

我是一个蟒蛇新手.我正在尝试使用python评估普朗克方程.我写了一个简单的程序.但是,当我给它输入时,给我一个错误.任何人都可以告诉我哪里出错了？这是程序和错误:

程序:

from __future__ import division
from sympy.physics.units import *
from math import *
import numpy
from scipy.interpolate import interp1d

#Planck's Law evaluation at a single wavelength and temperature
def planck_law(wavelength,temperature):
    T=temperature
    f=c/wavelength
    h=planck
    k=boltzmann
    U=2*h/(c**3)*(f**3)/(exp(h*f/(k*T))-1)
    return U.evalf()

输入:我已将函数导入为'cp',输入如下

value = (cp.planck_law(400,2000))

错误:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>`enter code here`
  File "Camera_performance.py", line 14, in planck_law
  U=2*h/(c**3)*(f**3)/(exp(h*f/(k*T))-1)
  File "/usr/lib/python2.7/dist-packages/sympy/core/expr.py", line 221, in __float__
  raise TypeError("can't convert expression to float")

TypeError: can't convert expression to float

Answer 1

看起来你正在混合命名空间,因为你正在使用它from ... import *.你想使用, sympy.exp()但你的代码使用math.exp().最好将名称空间分开,即永远不要使用from ... import *- 最初可能看起来更像打字,但最终会产生更清晰易懂的代码.尝试:

import sympy as sy
import sympy.physics.units as units

def planck_law(wavelength,temperature):
     """Planck's Law evaluation at a single wavelength and temperature """   
     T=temperature
     f=units.c/wavelength
     h=units.planck
     k=units.boltzmann
     U=2*h/(units.c**3)*(f**3)/(sy.exp(h*f/(k*T))-1)
     return U.evalf()

# Test:
print(planck_law(640e-9*units.m, 500*units.K))
# Result: 1.503553603007e-34*kg/(m*s)