在Python中反转代数表达式字符串的算法

Question

是否有一种简单的方法来使函数反转算法,例如:

>>> value = inverse("y = 2*x+3")
>>> print(value)
"x = (y-3)/2"

如果您无法为该功能制作实际代码,请向我推荐使这项任务更容易的工具.该函数仅用于与+, - ,*和/的逆算法.

Answer 1

您应该尝试SymPy来做到这一点:

from sympy import solve
from sympy.abc import x, y

e = 2*x+3-y

solve(e,x)
#[y/2 - 3/2]
solve(e,y)
#[2*x + 3]

基于此,您可以构建自己的inverse()喜欢(适用于两个变量):

def inverse(string, left_string=None):
    from sympy import solve, Symbol, sympify
    string = '-' + string
    e = sympify(string.replace('=','+'))
    if left_string:
        ans = left_string + ' = ' + str(solve(e, sympify(left_string))[0])
    else:
        left = sympify(string.split('=')[0].strip().replace('-',''))
        symbols = e.free_symbols
        symbols.remove( left )
        right = list(symbols)[0]
        ans = str(right) + ' = ' + str(solve(e, right)[0])
    return ans

例子:

inverse(' x = 4*y/2')
#'y = x/2'

inverse(' y = 100/x + x**2')
#'x = -y/(3*(sqrt(-y**3/27 + 2500) + 50)**(1/3)) - (sqrt(-y**3/27 + 2500) + 50)**(1/3)'

inverse("screeny = (isox+isoy)*29/2.0344827586206895", "isoy")
#'isoy = -isox + 0.0701545778834721*screeny'