title: No module named '_contextvars' in Python 3.7.3 virtual environment
body: <p>I'm working on a <strong>Django</strong> project which requires <strong>Python3.7.3</strong> virtual environment on <strong>Ubuntu 16</strong>.
  So I created a virtual environment and installed all the requirements in it and verified it, activated it.</p>
  
  <p>But when I try to run the <strong>Django</strong> server using <code>runserver</code> it is giving me below error.</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/lib/python3.7/decimal.py", line 3, in &lt;module&gt;
      from _decimal import *
  ModuleNotFoundError: No module named '_decimal'
  
  During handling of the above exception, another exception occurred:
  
      Traceback (most recent call last):
        File "./interfaces/control/manage.py", line 8, in &lt;module&gt;
          execute_from_command_line(sys.argv)
        File "/home/path/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
          utility.execute()
        File "/home/path/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
          self.fetch_command(subcommand).run_from_argv(self.argv)
        File "/home/path/lib/python3.7/site-packages/django/core/management/__init__.py", line 224, in fetch_command
          klass = load_command_class(app_name, subcommand)
        File "/home/path/lib/python3.7/site-packages/django/core/management/__init__.py", line 36, in load_command_class
          module = import_module('%s.management.commands.%s' % (app_name, name))
        File "/home/path/lib/python3.7/importlib/__init__.py", line 127, in import_module
          return _bootstrap._gcd_import(name[level:], package, level)
        File "&lt;frozen importlib._bootstrap&gt;", line 1006, in _gcd_import
        File "&lt;frozen importlib._bootstrap&gt;", line 983, in _find_and_load
        File "&lt;frozen importlib._bootstrap&gt;", line 967, in _find_and_load_unlocked
        File "&lt;frozen importlib._bootstrap&gt;", line 677, in _load_unlocked
        File "&lt;frozen importlib._bootstrap_external&gt;", line 728, in exec_module
        File "&lt;frozen importlib._bootstrap&gt;", line 219, in _call_with_frames_removed
        File "/home/path/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 10, in &lt;module&gt;
          from django.core.servers.basehttp import (
        File "/home/path/lib/python3.7/site-packages/django/core/servers/basehttp.py", line 17, in &lt;module&gt;
          from django.core.handlers.wsgi import LimitedStream
        File "/home/path/lib/python3.7/site-packages/django/core/handlers/wsgi.py", line 8, in &lt;module&gt;
          from django.core.handlers import base
        File "/home/path/lib/python3.7/site-packages/django/core/handlers/base.py", line 7, in &lt;module&gt;
          from django.urls import get_resolver, set_urlconf
        File "/home/path/lib/python3.7/site-packages/django/urls/__init__.py", line 1, in &lt;module&gt;
          from .base import (
        File "/home/path/lib/python3.7/site-packages/django/urls/base.py", line 4, in &lt;module&gt;
          from django.utils.encoding import iri_to_uri
        File "/home/path/lib/python3.7/site-packages/django/utils/encoding.py", line 4, in &lt;module&gt;
          from decimal import Decimal
        File "/usr/lib/python3.7/decimal.py", line 8, in &lt;module&gt;
          from _pydecimal import *
        File "/usr/lib/python3.7/_pydecimal.py", line 436, in &lt;module&gt;
          import contextvars
        File "/usr/lib/python3.7/contextvars.py", line 1, in &lt;module&gt;
          from _contextvars import Context, ContextVar, Token, copy_context
      ModuleNotFoundError: No module named '_contextvars'
  </code></pre>
  
  <p>Note that it is first going to Django project in my <code>virtualenv</code> here.</p>
  
  <pre><code>/home/path/lib/python3.7/site-packages/django/core/management/__init__.py
  </code></pre>
  
  <p>Again it is searching in the global location of python here.</p>
  
  <pre><code>/usr/lib/python3.7/_pydecimal.py
  </code></pre>
  
  <p>Can someone please let me know why it is going to the global location and throwing the error.</p>