获取数学函数作为用户输入 [英] Getting mathematical function as user's input

问题描述

我需要知道如何将字符串输入转换为可执行函数. 例如-用户编写字符串'x * Sin(x ** 2)'，然后programm将其用作函数，可以为给定的x计算值，可以绘制此函数的派生等. scitools.stringfunction，但据我所知，此模块在python-3中不可调用.

I need to know how transfer string input into executable function. For example - user write string 'x*Sin(x**2)' and then programm takes it as function, can calculate a value for given x, can plot derivation of this function etc. I've read that there is module called scitools.stringfunction, but as far as I know this module is not callable in python-3.

任何想法如何实现?

推荐答案

像这样:

from sympy import var
from sympy import sympify

x = var('x')  # the possible variable names must be known beforehand...
user_input = 'x * sin(x**2)'
expr = sympify(user_input)
res = expr.subs(x, 3.14)
print(res)  # -1.322...

如果要将用户输入转换为函数，可以调用此函数:

if you want to turn the user input into a function you can call you could to this:

from sympy.utilities.lambdify import lambdify
f = lambdify(x, expr)
# f(3.14) -> -1.322...

sympy可以进行符号计算(包括导数)；如果要绘制图，我强烈建议 matplotlib .

sympy can do sybolic calculations (including derivatives); if you want to make plots i strongly suggest matplotlib.

使用与eval相对的数学库的优点是您不需要清理用户输入(针对恶意代码).
(由于 ejm 的评论而删除了此内容.)

the advantage of using a math library opposed to eval is that you do not need to sanitize the user input (against malicious code).
(deleted this thanks to a comment from ejm).

这篇关于获取数学函数作为用户输入的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！