Proper way to implement user input with Sympy?-CodePudding

I am currently working on creating a python script that will do a series of calculations based on the formula entered by the user; however, it is not working as expected?

I have tried the following:

init_printing(use_unicode=True)

x, y = symbols('x y', real = True)
userinput = sympify(input("testinput: "))

x_diff = diff(userinput, x)

print(x_diff)

However, this always returns zero, but when I write the input directly, e.g.

init_printing(use_unicode=True)

x, y = symbols('x y', real = True)
userinput = x**0.5 y

x_diff = diff(userinput, x)

print(x_diff)

It works flawlessly, what am I doing wrong here?

Thanks!

CodePudding user response：

Adding locals parameter in sympify function will help you. Here is a working code, based on yours :

from sympy import *

init_printing(use_unicode=True)

x, y = symbols('x y', real = True)
userinput = input("testinput: ")
locals = {'x':x, 'y':y}
sympified = sympify(userinput, locals=locals)
print(f'derivate /x : = \n {diff(sympified, x)} \n derivative / y : \n {diff(sympified, y)}')

Output:

testinput: cos(y)   2*x

derivate /x :
2
derivative /y :
-sin(y)