title: How to get coefficients in sympy expression/ Python
body: <p>How to get coefficients in sympy expression</p>
  
  <pre><code>b = sympy.Symbol('b')
  a = sympy.Symbol('a')
  x = sympy.Symbol('x')
  
  y = 2*x**3 + a*x**2 +b*x
  </code></pre>
  
  <p>The result should be : </p>
  
  <p><code>coeff for x**3 =2
  coeff for x**2 = a
  coeff for x = b</code></p>