human
Solve the following python programming problem given the following code:
@ classmethod 
def _init_mode(cls) : 
    "
        Initializes the plot mode based on
        the 'mode-specific parameters' above.
        Only intended to be called by
        PlotMode._register(). To use a mode without
        registering it, you can directly call
        ModeSubclass._init_mode().
        " 
    def symbols_list(symbol_str) : 
        return [Symbol (s) for s in symbol_str] 
cls.i_vars = symbols_list (cls.i_vars) 
    cls.d_vars = symbols_list (cls.d_vars) 
    cls.i_var_count = len (cls.i_vars) 
    cls.d_var_count = len (i.d_vars) 
    if (cls.i_var_count > PlotMode._i_var_max) : 
        raise ValueError (var_count_error (True, False)) 
if (cls.d_var_count > PlotMode._d_var_max) : 
        raise ValueError (var_count_error (False, False)) 
if (len (cls.aliases) > 0) : 
        cls.primary_alias = cls.aliases [0] 
else : 
        cls.primary_alias = cls.__name__ 
di = cls.intervals 
    if (len (di) != cls.i_var_count) : 
        raise ValueError ('Plot mode must provide a default interval for each i_var.') 
for i in range (cls.i_var_count) : 
        if (len (di [i]) != 3) : 
            raise ValueError ('length should be equal to 3') 
di [i] = PlotInterval (None, * di [i]) 
cls._was_initialized = True 

    
    

    Fix the buggy line: cls.d_var_count = len (i.d_vars)
assistant
#Here is Python program to fix the buggy line: cls.

cls.d_var_count = len (cls.d_vars)