old_contents: # This is the only location where the version will be written and changed.
  # Based on https://packaging.python.org/single_source_version/
  __version__ = '0.21.0b'
  
new_contents: # This is the only location where the version will be written and changed.
  # Based on https://packaging.python.org/single_source_version/
  __version__ = '0.21.0'
  
subject: update master to v0.21.0