Determine individual terms of SymPy expression

Question

For a project I am working on I have to select a specific term from an arbitrary SymPy expression. For this I am using .args which works fine if the expression consists of multiple distinct terms, but returns the individual coefficients in the term if only a single term is present. See the following example:

import sympy as sym

x, c0, c1 = sym.symbols('x c0 c1')

f0 = c0*x
f1 = c1*x**2
f2 = c0*x + c1*x**2

print(f0.args) # Output: (c0, x)    Desired: (c0*x)
print(f1.args) # Output: (c1, x**2) Desired: (c1*x**2)
print(f2.args) # Output: (c0*x, c1*x**2)

This method works as I would want it to for f2, where it returns (c0*x, c1*x**2). For f0 and f1 however it returns the coefficients c0, c1 and x separately. How would I go achieving the desired output where for the single term expressions the coefficients and x are also returned as a multiplicative expression?

Note that ideally I would want this method to work for any form of expression, with arbitrary dependencies on x and an arbitrary amount of coefficients.

Answer 1

You need to use poly to state the fact that you have polynomials:

import sympy as sym
from sympy import symbols, Poly


x, c0, c1 = sym.symbols('x c0 c1')

f0 = sym.poly(c0*x)
f1 = sym.poly(c1*x**2)
f2 = c0*x + c1*x**2

print(f0.args) # Output: (c0, x)    Desired: (c0*x)
print(f1.args) # Output: (c1, x**2) Desired: (c1*x**2)
print(f2.args) # Output: (c0*x, c1*x**2)

returns

(c0*x, x, c0)
(c1*x**2, x, c1)
(c0*x, c1*x**2)

to get the monimials, simply use

f0.args[0]

which gives

c0*x