title: My pyinstaller is giving Assertion Error when I execute it
body: <p>Running other scripts gives no problem. Something about package distribution is raising the exception.</p>
  
  <p>I am able to successfully execute and create .exe files from other scripts, even previous version of this script. </p>
  
  <p>My python version is 3.7 and pyinstaller version is 3.4. Running on Windows 10 64-bit OS.</p>
  
  <p>Thanks in advance.</p>
  
  <pre><code>Traceback (most recent call last):
    File "c:\program files\python37\lib\runpy.py", line 193, in _run_module_as_main
      "__main__", mod_spec)
    File "c:\program files\python37\lib\runpy.py", line 85, in _run_code
      exec(code, run_globals)
    File "C:\Program Files\Python37\Scripts\pyinstaller.exe\__main__.py", line 9, in &lt;module&gt;
    File "c:\program files\python37\lib\site-packages\PyInstaller\__main__.py", line 111, in run
      run_build(pyi_config, spec_file, **vars(args))
    File "c:\program files\python37\lib\site-packages\PyInstaller\__main__.py", line 63, in run_build
      PyInstaller.building.build_main.main(pyi_config, spec_file, **kwargs)
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\build_main.py", line 838, in main
      build(specfile, kw.get('distpath'), kw.get('workpath'), kw.get('clean_build'))
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\build_main.py", line 784, in build
      exec(text, spec_namespace)
    File "&lt;string&gt;", line 17, in &lt;module&gt;
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\build_main.py", line 241, in __init__
      self.__postinit__()
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\datastruct.py", line 158, in __postinit__
      self.assemble()
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\build_main.py", line 521, in assemble
      deps_proc = DependencyProcessor(self.graph, additional_files_cache)
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\toc_conversion.py", line 49, in __init__
      self._distributions.update(self._get_distribution_for_node(node))
    File "c:\program files\python37\lib\site-packages\PyInstaller\building\toc_conversion.py", line 86, in _get_distributi
  on_for_node
      assert len(dists) == 1
  AssertionError
  </code></pre>