How to get a list of coefficients of an expression in SymPy?

Question

Lets say I have an expression like this in SymPy:

s = sp.symbols('s')
Y = s**3 + 3*s**2 + 2*s
Y

Now I would like to get a "list of orders" of that expression. here is an example of what I want to achieve: I would like to create a tf() object. Where tf() is a function like in Matlab that takes two lists, a denominator, and a numerator, and creates a transfer function out of them:

tf([1], [1, 3, 2, 0])

I would like to extract those two lists from my SymPy expression to use them like in that tf() function. How can I do that?

Do you maybe need [this](https://stackoverflow.com/a/24127329)? — user8408080, Dec 30 '20 at 19:03
`sp.Poly(s**3 + 3*s**2 + 2*s, s).all_coeffs()` does the job! Thank you!!! — John, Dec 30 '20 at 19:11

score 2 · Accepted Answer · answered Dec 30 '20 at 19:13

2

After transforming an expression into a polynomial all_coeffs() does the job:

sp.Poly(s**3 + 3*s**2 + 2*s, s).all_coeffs()

[1, 3, 2, 0]

answered Dec 30 '20 at 19:13

John

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How to get a list of coefficients of an expression in SymPy?

1 Answers1