old_contents: from __future__ import absolute_import
  
  from toil import version
  import logging
  
  logger = logging.getLogger(__name__)
  
  
  def addBasicProvisionerOptions(parser):
      parser.add_argument("--version", action='version', version=version)
      parser.add_argument('-p', "--provisioner", dest='provisioner', choices=['aws', 'azure', 'gce'], required=False, default="aws",
                          help="The provisioner for cluster auto-scaling. Only aws is currently "
                               "supported")
      try:
          from toil.provisioners.aws import getCurrentAWSZone
          currentZone = getCurrentAWSZone()
      except ImportError:
          currentZone = None
      zoneString = currentZone if currentZone else 'No zone could be determined'
      parser.add_argument('-z', '--zone', dest='zone', required=False, default=currentZone,
                          help="The AWS availability zone of the master. This parameter can also be "
                               "set via the TOIL_AWS_ZONE environment variable, or by the ec2_region_name "
                               "parameter in your .boto file, or derived from the instance metadata if "
                               "using this utility on an existing EC2 instance. "
                               "Currently: %s" % zoneString)
      parser.add_argument("clusterName", help="The name that the cluster will be identifiable by. "
                                              "Must be lowercase and may not contain the '_' "
                                              "character.")
      return parser
  
new_contents: from __future__ import absolute_import
  
  from toil import version
  import logging
  import os
  logger = logging.getLogger(__name__)
  
  
  def addBasicProvisionerOptions(parser):
      parser.add_argument("--version", action='version', version=version)
      parser.add_argument('-p', "--provisioner", dest='provisioner', choices=['aws', 'azure', 'gce'], required=False, default="aws",
                          help="The provisioner for cluster auto-scaling. Only aws is currently "
                               "supported")
      parser.add_argument('-z', '--zone', dest='zone', required=False, default=None,
                          help="The availability zone of the master. This parameter can also be set via the 'TOIL_X_ZONE' "
                               "environment variable, where X is AWS, GCE, or AZURE, or by the ec2_region_name parameter "
                               "in your .boto file, or derived from the instance metadata if using this utility on an "
                               "existing EC2 instance.")
      parser.add_argument("clusterName", help="The name that the cluster will be identifiable by. "
                                              "Must be lowercase and may not contain the '_' "
                                              "character.")
      return parser
  
  
  def getZoneFromEnv(provisioner):
      """
      Find the zone specified in an environment variable.
  
      The user can specify zones in environment variables in leiu of writing them at the commandline every time.
      Given a provisioner, this method will look for the stored value and return it.
      :param str provisioner: One of the supported provisioners ('azure', 'aws', 'gce')
      :rtype: str
      :return: None or the value stored in a 'TOIL_X_ZONE' environment variable.
      """
  
      return os.environ.get('TOIL_' + provisioner.upper() + '_ZONE')
  
subject: Remove default for zone, add method for searching for specified zone in environ vars.