docs: def mac_app_exists(app):
  	'''Check if 'app' is installed (OS X).
  
  	Check if the given applications is installed on this OS X system.
  
  	Args:
  			app (str): The application name.
  
  	Returns:
  			bool: Is the app installed or not?
  	'''
  
  	APP_CHECK_APPLESCRIPT = '''try
  	tell application "Finder"
  		set appname to name of application file id "%s"
  		return 0
  	end tell
  	on error err_msg number err_num
  		return 1
  	end try'''
  
  	with open('/tmp/app_check.AppleScript', 'w') as f:
  		f.write(APP_CHECK_APPLESCRIPT % app)
  
  	app_check_proc = sp.Popen(
  		['osascript', '-e', '/tmp/app_check.AppleScript'])
  
  	if app_check_proc.wait() != 0:
  		return False
  
  	else:
  		return True