python计算bleu代码带有惩罚因子

Sure! To calculate BLEU score with a penalty factor (also known as brevity penalty), you can use the `SmoothingFunction` class from the `nltk.translate.bleu_score` module. Here's an example code:

import nltk
from nltk.translate.bleu_score import sentence_bleu, SmoothingFunction

# Reference sentence
reference = ['The cat is on the mat']

# Candidate sentence
candidate = ['The cat is on the mat']

# Calculate BLEU score with penalty
smoothing = SmoothingFunction().method4
bleu_score = sentence_bleu([reference], candidate, smoothing_function=smoothing)

print("BLEU score with penalty:", bleu_score)

In this code, we import the `sentence_bleu` function and the `SmoothingFunction` class from `nltk.translate.bleu_score` module. We create an instance of `SmoothingFunction` with `method4` as the smoothing method, which is a commonly used method for calculating brevity penalty.

Then, we use the `sentence_bleu` function and pass the reference sentence (`[reference]`), candidate sentence (`candidate`), and the smoothing method instance (`smoothing`) to calculate the BLEU score with penalty.

You can experiment with different smoothing methods by using `method1`, `method2`, `method3`, or `method5`.

Remember to have the `nltk` library installed before running this code. Let me know if you have any further questions!