Callback reader
***************

*CallbackReader* class instance tries to fetch MIB files by calling
user object.

class pysmi.reader.callback.CallbackReader(cbFun, cbCtx=None)

   Fetch ASN.1 MIB text by name by calling user-defined callable.

   *CallbackReader* class instance tries to retrieve ASN.1 MIB files
   by name and return their contents to caller.

   Create an instance of *CallbackReader* bound to specific URL.

   Parameters:
      **cbFun** (*callable*) -- user callable accepting *MIB name* and
      *cbCtx* objects

   Keyword Arguments:
      **cbCtx** (*object*) -- user object that can be used to
      communicate state information between user-scope code and the
      *cbFun* callable scope
