def var_num(self, varname):
    "Get the variable number of a particular variable name\n\n        This maintains a cache of name-to-number mappings for zVariables\n        to keep from having to query the CDF library constantly. It's mostly\n        an internal function.\n\n        Parameters\n        ==========\n        varname : bytes\n            name of the zVariable. Not this is NOT a string in Python 3!\n\n        Raises\n        ======\n        CDFError : if variable is not found\n\n        Returns\n        =======\n        out : int\n            Variable number of this zvariable.\n        "
    num = self._var_nums.get(varname, None)
    if (num is None):
        varNum = ctypes.c_long(0)
        self._call(const.GET_, const.zVAR_NUMBER_, varname, ctypes.byref(varNum))
        num = varNum.value
        self._var_nums[varname] = num
    return num
Get the variable number of a particular variable name

This maintains a cache of name-to-number mappings for zVariables
to keep from having to query the CDF library constantly. It's mostly
an internal function.

Parameters
==========
varname : bytes
    name of the zVariable. Not this is NOT a string in Python 3!

Raises
======
CDFError : if variable is not found

Returns
=======
out : int
    Variable number of this zvariable.
def var_num(self, varname):
    "Get the variable number of a particular variable name\n\n        This maintains a cache of name-to-number mappings for zVariables\n        to keep from having to query the CDF library constantly. It's mostly\n        an internal function.\n\n        Parameters\n        ==========\n        varname : bytes\n            name of the zVariable. Not this is NOT a string in Python 3!\n\n        Raises\n        ======\n        CDFError : if variable is not found\n\n        Returns\n        =======\n        out : int\n            Variable number of this zvariable.\n        "
    num = self._var_nums.get(varname, None)
    if (num is None):
        varNum = ctypes.c_long(0)
        self._call(const.GET_, const.zVAR_NUMBER_, varname, ctypes.byref(varNum))
        num = varNum.value
        self._var_nums[varname] = num
    return num