title: Tricomi Hypergeometric U in Python
body: <p>There is <strong><em>sympy</em></strong> package in Python for doing symbolic computation. It has most of the hypergeometric functions. However, I am unable to find the specific <a href="http://functions.wolfram.com/webMathematica/FunctionEvaluation.jsp?name=HypergeometricU" rel="nofollow noreferrer">Tricomi confluent hypergeometric function.</a>  </p>
  
  <p>My requirement is pretty basic. For e.g. if we specify U(a,b,x), I want to get the first 5-10 terms of this expansion. <strong><em>sympy</em></strong> package has the <em>expand</em> function but it does not have the Tricomi hypergeometric U function. Any help is appreciated. </p>
  
  <p>Edit: 
  As some users suggested, I set out to write my own function. However, I am unable to expand even the basic ones. Can someone give a reproducible example for me to play around with? Thank you </p>
  
  <pre><code>from sympy import *
  x, y, z, t = symbols('x y z t')
  expand_func(hyper([y],[z],x))
  </code></pre>