title: I got ModuleNotFoundError: No module named 'Cython' when trying to make Extension
body: <p>I'm trying to run this code :</p>
  <pre><code>from distutils.core import setup
  from distutils.extension import Extension
  from Cython.Distutils import build_ext
  ext_modules = [
      Extension(&quot;sum&quot;,  [&quot;a123.pyx&quot;])]
  
  setup(
      name = 'app',
      cmdclass = {'build_ext': build_ext},
      ext_modules = ext_modules
  )
  </code></pre>
  <p>and I got this Error :</p>
  <pre><code>Traceback (most recent call last):
    File &quot;compile.py&quot;, line 3, in &lt;module&gt;
      from Cython.Distutils import build_ext
  ImportError: No module named 'Cython'
  </code></pre>
  <p>I'm using Conda and I add cython to it also I'm installing cython in my system.but error doesnot fix!</p>