code: def get_valid_varname(varname):
      
      vname = varname
      for s, r in VARNAME_MAP_CHAR:
          vname = vname.replace(s, r)
  
      return vname
docs: Replace characters (e.g., ':', '$', '=', '-') of a variable name, which
      may cause problems when using with (CF-)netCDF based packages.
  
      Parameters
      ----------
      varname : string
          variable name.
  
      Notes
      -----
      Characters replacement is based on the table stored in
      :attr:`VARNAME_MAP_CHAR`.