Finding coefficients of x in a string

Question

I am trying to make an algebra solver, so I have to find the coefficients of x in an expression. Currently this is the code I have to take an input:

equation = input("Enter equation: ")
LHS, RHS = equation.split("=")[0], equation.split("=")[1]

##Remove whitespaces
LHS, RHS = LHS.replace(" ",""), RHS.replace(" ","")

Now I want to get the coefficients of x in the expressions LHS and RHS, how can I do this? And also, the coefficients may not be just numbers but they may be of the form (2*3+4)x. I think this can be done using the eval() function but I don't know how to apply it.

Note: I want to do this with plain python, without using any modules which are not built-in.

Can you give an example of a valid input and the expected output? — Thaer A, Apr 19 '20 at 10:58
@Thaer A If the input was "2-(2+4*5)x +3x" then output would be ["2-(2+4*5)", "3"] or any other variable containing the coefficients. — Sujal Motagi, Apr 19 '20 at 11:26

J. Doe · Answer 1 · 2020-04-19T11:39:54.613

0

In case it's only one variable and thus only one coefficient you could divide the respective variable/site by x. Taking your example:

(2*3+4)x

dividing by x gives us the coefficient:

(2*3.4)

If that's not the approach you want to take, you could also convert the expression into a string and exclude "x", as such:

coefficientLHS = LHS.replace("x", "")

However, you should use this cautious as you might have algebra expressions in front of your variable, so regex implementation would be advisable.

Another approach would be to use the module Poly:

x = symbols("x")
coefLHS = Poly(LHS, x)
coefLHS.coeffs()

edited Apr 19 '20 at 11:39

answered Apr 19 '20 at 10:59

J. Doe

61
1
2
9

Yes there will be algebra expressions in front of the x, so this approach won't work without some extra processing. – Sujal Motagi Apr 19 '20 at 11:24
What about using the module Poly? I edit my solution, take a look at it. :) – J. Doe Apr 19 '20 at 11:36

Finding coefficients of x in a string

1 Answers1