掩码语言模型
BERT 如何从原始文本中学习
掩码语言模型 是 CoddyKit 上的免费 NLP Academy 课时。 这是第 2 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 NLP Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 NLP Academy 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Learning Without Labels
BERT trains on plain text with no human labels at all. This clever trick is called self-supervised learning.
The Fill-in-the-Blank Game
BERT learns by hiding some words and guessing them back. That game is masked language modeling, or MLM for short.
Hiding a Word
A random word gets swapped for a special placeholder. Here the model must recover what the mask is covering up.
text = "the cat sat on the [MASK]"
# model should predict: matPredict the Missing Word
BERT reads everything around the blank and ranks likely fills. Strong guesses come from using the full context.
Why Hiding Helps
To fill a blank well, the model must learn grammar, facts, and word relationships. The blank forces real understanding.
The Famous 15 Percent
BERT masks about 15 percent of the words in each sentence during training. That ratio balances signal and difficulty.
Both Sides at Once
Unlike left-to-right models, BERT sees words before and after the blank. This bidirectional view makes its guesses far richer.
A Second Task
Original BERT also guessed if one sentence follows another. That extra job is next sentence prediction, teaching it about flow.
Pre-training, Then Reuse
This slow, expensive MLM phase is the pre-training step. You download the result and reuse it without redoing the work.
Try It in Code
A fill-mask pipeline lets you watch MLM in action and see BERT rank its top predictions for any blank.
from transformers import pipeline
fm = pipeline("fill-mask", model="bert-base-uncased")
fm("Paris is the [MASK] of France.")Knowledge for Free
After MLM, BERT holds a huge store of language knowledge ready to power your tasks. All of it came from raw text.
Quick Check
What does masked language modeling ask BERT to do?
Recap
BERT learns by filling masked blanks using both sides of a sentence. This self-supervised MLM builds deep language knowledge. ✅
常见问题解答
「掩码语言模型」课时是免费的吗？
是的 — 「掩码语言模型」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 NLP Academy 课程的其余内容，请升级到 CoddyKit PRO。 NLP Academy 课程共包含 4 节课。
「掩码语言模型」这节课中我会学到什么？
BERT 如何从原始文本中学习 你通过在浏览器中直接运行的动手代码来练习 NLP Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 NLP Academy 需要有经验吗？
无需任何先前经验。CoddyKit 上的 NLP Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 2 节课，共 4 节。
「掩码语言模型」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 NLP Academy 课中编写并运行代码吗？
能。每节 NLP Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。