functions.py

from tiktoken import encoding_for_model,get_encoding

def num_tokens_from_messages(messages, model="gpt-3.5-turbo-0301"):
	"""Returns the number of tokens used by a list of messages."""
	try:
		encoding = encoding_for_model(model)
	except KeyError:
		encoding = get_encoding("cl100k_base") # model not found. using cl100k_base encoding.
	if model == "gpt-3.5-turbo": 
		return num_tokens_from_messages(messages, model="gpt-3.5-turbo-0301")
	elif model == "gpt-4":
		return num_tokens_from_messages(messages, model="gpt-4-0314")
	elif model == "gpt-3.5-turbo-0301":
		tokens_per_message = 4  # every message follows <|start|>{role/name}\n{content}<|end|>\n
		tokens_per_name = -1  # if there's a name, the role is omitted
	elif model == "gpt-4-0314":
		tokens_per_message = 3
		tokens_per_name = 1
	else:
		raise NotImplementedError(f"""num_tokens_from_messages() is not implemented for model {model}. See https://github.com/openai/openai-python/blob/main/chatml.md for information on how messages are converted to tokens.""")
	num_tokens = 0
	for message in messages:
		num_tokens += tokens_per_message
		for key, value in message.items():
			num_tokens += len(encoding.encode(value))
			if key == "name":
				num_tokens += tokens_per_name
	num_tokens += 3  # every reply is primed with <|start|>assistant<|message|>
	return num_tokens