How to calculate the tokens when using function call

Python function if anyone needs it:

    def num_tokens_from_functions(functions, model="gpt-3.5-turbo-0613"):
        """Return the number of tokens used by a list of functions."""
        try:
            encoding = tiktoken.encoding_for_model(model)
        except KeyError:
            print("Warning: model not found. Using cl100k_base encoding.")
            encoding = tiktoken.get_encoding("cl100k_base")
        
        num_tokens = 0
        for function in functions:
            function_tokens = len(encoding.encode(function['name']))
            function_tokens += len(encoding.encode(function['description']))
            
            if 'parameters' in function:
                parameters = function['parameters']
                if 'properties' in parameters:
                    for propertiesKey in parameters['properties']:
                        function_tokens += len(encoding.encode(propertiesKey))
                        v = parameters['properties'][propertiesKey]
                        for field in v:
                            if field == 'type':
                                function_tokens += 2
                                function_tokens += len(encoding.encode(v['type']))
                            elif field == 'description':
                                function_tokens += 2
                                function_tokens += len(encoding.encode(v['description']))
                            elif field == 'enum':
                                function_tokens -= 3
                                for o in v['enum']:
                                    function_tokens += 3
                                    function_tokens += len(encoding.encode(o))
                            else:
                                print(f"Warning: not supported field {field}")
                    function_tokens += 11

            num_tokens += function_tokens

        num_tokens += 12 
        return num_tokens
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