text: #-----------------------------------------------------------------------------
  # Copyright (c) 2012 - 2020, Anaconda, Inc., and Bokeh Contributors.
  # All rights reserved.
  #
  # The full license is in the file LICENSE.txt, distributed with this software.
  #-----------------------------------------------------------------------------
  ''' Utilities for checking dependencies
  
  '''
  
  #-----------------------------------------------------------------------------
  # Boilerplate
  #-----------------------------------------------------------------------------
  import logging # isort:skip
  log = logging.getLogger(__name__)
  
  #-----------------------------------------------------------------------------
  # Imports
  #-----------------------------------------------------------------------------
  
  # Standard library imports
  from importlib import import_module
  from types import ModuleType
  from typing import Optional
  
  #-----------------------------------------------------------------------------
  # Globals and constants
  #-----------------------------------------------------------------------------
  
  __all__ = (
      'import_optional',
      'import_required',
  )
  
  #-----------------------------------------------------------------------------
  # General API
  #-----------------------------------------------------------------------------
  
  def import_optional(mod_name: str) -> Optional[ModuleType]:
      ''' Attempt to import an optional dependency.
  
      Silently returns None if the requested module is not available.
  
      Args:
          mod_name (str) : name of the optional module to try to import
  
      Returns:
          imported module or None, if import fails
  
      '''
      try:
          return import_module(mod_name)
      except ImportError:
          pass
      except Exception:
          msg = "Failed to import optional module `{}`".format(mod_name)
          log.exception(msg)
  
      return None
  
  
  def import_required(mod_name: str, error_msg: str) -> ModuleType:
      ''' Attempt to import a required dependency.
  
      Raises a RuntimeError if the requested module is not available.
  
      Args:
          mod_name (str) : name of the required module to try to import
          error_msg (str) : error message to raise when the module is missing
  
      Returns:
          imported module
  
      Raises:
          RuntimeError
  
      '''
      try:
          return import_module(mod_name)
      except ImportError as e:
          raise RuntimeError(error_msg) from e
  
  #-----------------------------------------------------------------------------
  # Dev API
  #-----------------------------------------------------------------------------
  
  #-----------------------------------------------------------------------------
  # Private API
  #-----------------------------------------------------------------------------
  
  #-----------------------------------------------------------------------------
  # Code
  #-----------------------------------------------------------------------------
  