code: def set_version(new_version_number=None, old_version_number=''):
      
      if new_version_number is None:
          return ValueError
  
      import fileinput
      import sys
  
      file = join('timezonefinder', '__init__.py')
  
      for line in fileinput.input(file, inplace=1):
          if old_version_number in line:
              line = line.replace(old_version_number, new_version_number)
          sys.stdout.write(line)
docs: Set package version as listed in `__version__` in `__init__.py`.