class_docstr: This class can be used to fetch NuPic configuration settings which are
  stored in one or more XML files.
  
  If the environment variable ``NTA_CONF_PATH`` is defined, then the
  configuration files are expected to be in the ``NTA_CONF_PATH`` search path,
  which is a ':' separated list of directories (on Windows the separator is a
  ';'). If ``NTA_CONF_PATH`` is not defined, then it is loaded via
  pkg_resources.
docstr: Retrieve the requested property as a string. If property does not exist,
  then KeyError will be raised.
  
  :param prop: (string) name of the property
  :raises: KeyError
  :returns: (string) property value
docstr_tok: ["Retrieve","the","requested","property","as","a","string",".","If","property","does","not","exist",",","then","KeyError","will","be","raised",".",":","param","prop",":","(","string",")","name","of","the","property",":","raises",":","KeyError",":","returns",":","(","string",")","property","value"]
code: def getString(cls, prop):
      """Retrieve the requested property as a string. If property does not exist,
      then KeyError will be raised.
  
      :param prop: (string) name of the property
      :raises: KeyError
      :returns: (string) property value
      """
      if cls._properties is None:
          cls._readStdConfigFiles()
  
      # Allow configuration properties to be overridden via environment variables
      envValue = os.environ.get(
          "%s%s" % (cls.envPropPrefix, prop.replace(".", "_")), None
      )
      if envValue is not None:
          return envValue
  
      return cls._properties[prop]
  
imports: from __future__ import with_statement
  import os
  import logging
  from xml.etree import ElementTree
  from pkg_resources import resource_string
label_desc: Use image node_id 1 for calling the Configuration obj's underlying member method code with example usage: obj.getString(cls, prop) and returns: cls, envValue