title: Python OverflowError : in method 'get_GDSII_prisms', argument 3 of type 'int'
body: <p>I'm a new user of a Python module called <a href="https://github.com/NanoComp/meep" rel="nofollow noreferrer">meep</a>. I followed <a href="https://meep.readthedocs.io/en/latest/Python_Tutorials/GDSII_Import/" rel="nofollow noreferrer">this tutorial</a> and everything works fine. However, I tried to change something and I keep having the same error : <strong>OverflowError : in method 'get_GDSII_prisms', argument 3 of type 'int'</strong></p>
  <p>Here is the part of the code that causes trouble :</p>
  <pre><code>gdsII_file = 'coupler.gds'
  UPPER_BRANCH_LAYER = 31
  si_zmax = 10
  si_zmin = -10
  
  def test(p):
      return mp.Medium(index=15)
      
  upper_branch = mp.get_GDSII_prisms(test, gdsII_file, UPPER_BRANCH_LAYER, si_zmin, si_zmax)
  </code></pre>
  <p>The only change I made is that I put a function as first argument of get_GDSII_prisms instead of a mp.Medium instance (calling <code>mp.get_GDSII_prisms(mp.Medium(index=15), gdsII_file, UPPER_BRANCH_LAYER, si_zmin, si_zmax</code> doesn't create any trouble.) But this should work since every function of this module that takes a mp.Medium instance can also take a user-defined function. Moreover, I found it strange that Python finds an error on argument 3 whereas I only changed argument 1.</p>
  <p>I looked on the internet in order to understand why I have this error and how to resolve it but I didn't found anything.</p>
  <p>I'm using Python 3.8.5.</p>
  <p>Thank you for your help!</p>