old_contents: import os
  import re
  
  from helper import *
  import unix_windows
  
  
  section("Preparing virtualenv")
  
  # check that virtualenv installed
  if not executable_exists('virtualenv'):
      fail("""\
  Please install virtualenv!
  
  https://github.com/pypa/virtualenv
  
  {}""".format(unix_windows.VIRTUALENV_INSTALL_MSG))
  
  # Make sure that not running in virtualenv
  if hasattr(sys, 'real_prefix'):
      fail("""Please exit virtualenv!""")
  
  # Check if 'env' already exists + is virtualenv
  virtualenv_exists = False
  if os.path.isdir("env"):
      if shell(unix_windows.VIRTUALENV_CMD).success():
          virtualenv_exists = True
  
  
  # Create virtualenv if necessary
  if not virtualenv_exists:
      if unix_windows.IS_WIN:
          shell("virtualenv env").should_not_fail()
      else:
          shell("virtualenv env --python=python3").should_not_fail()
  
new_contents: import os
  import re
  
  from helper import *
  import unix_windows
  
  
  section("Preparing virtualenv")
  
  # check that virtualenv installed
  virtualenv_installed = False
  
  if unix_windows.IS_WIN:
      virtualenv_installed = shell(unix_windows.VIRTUALENV_CMD + ' -h').success()
  else:
      virtualenv_installed = executable_exists('virtualenv')
  
  
  if not virtualenv_installed:
      fail("""\
  Please install virtualenv!
  
  https://github.com/pypa/virtualenv
  
  {}""".format(unix_windows.VIRTUALENV_INSTALL_MSG))
  
  # Make sure that not running in virtualenv
  if hasattr(sys, 'real_prefix'):
      fail("""Please exit virtualenv!""")
  
  # Check if 'env' already exists + is virtualenv
  virtualenv_exists = False
  if os.path.isdir("env"):
      if shell(unix_windows.VIRTUALENV_CMD).success():
          virtualenv_exists = True
  
  
  # Create virtualenv if necessary
  if not virtualenv_exists:
      if unix_windows.IS_WIN:
          shell("py -3 -m virtualenv env").should_not_fail()
      else:
          shell("virtualenv env --python=python3").should_not_fail()
  
subject: Change Windows virtualenv command