ERROR: gcloud failed to load: module ‘collections’ has no attribute ‘Mapping’ が出た時

ERROR: gcloud failed to load: module 'collections' has no attribute 'Mapping'
    gcloud_main = _import_gcloud_main()
    import googlecloudsdk.gcloud_main
    from googlecloudsdk.calliope import cli
    from googlecloudsdk.calliope import actions
    from googlecloudsdk.calliope import markdown
    from googlecloudsdk.calliope import usage_text
    from googlecloudsdk.calliope import parser_arguments
    from googlecloudsdk.calliope import parser_completer
    from googlecloudsdk.core.console import progress_tracker
    class _BaseStagedProgressTracker(collections.Mapping):

This usually indicates corruption in your gcloud installation or problems with your Python interpreter.

Please verify that the following is the path to a working Python 2.7 or 3.5+ executable:
    /usr/local/bin/python3

If it is not, please set the CLOUDSDK_PYTHON environment variable to point to a working Python 2.7 or 3.5+ executable.

If you are still experiencing problems, please reinstall the Cloud SDK using the instructions here:
    https://cloud.google.com/sdk/

 export CLOUDSDK_PYTHON="/usr/bin/python2"