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BpeTokenizer Cleanup #7514

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merged 2 commits into from
Oct 3, 2025
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BpeTokenizer Cleanup #7514

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18c7913
BpeTokenizer Cleanup
tarekgh Oct 2, 2025
0aea52c
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tarekgh Oct 2, 2025
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35 changes: 17 additions & 18 deletions src/Microsoft.ML.Tokenizers/Model/BPETokenizer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -320,7 +320,7 @@ private BpeTokenizer(

if (beginningOfSentenceToken is not null)
{
if (!_vocab.TryGetValue(beginningOfSentenceToken, out int aId))
if (_vocab.TryGetValue(beginningOfSentenceToken, out int aId) is false && specialTokens?.TryGetValue(beginningOfSentenceToken, out aId) is false)
{
throw new InvalidOperationException($"The beginning of sentence token '{beginningOfSentenceToken}' was not present in the vocabulary.");
}
Expand All @@ -331,7 +331,7 @@ private BpeTokenizer(

if (endOfSentenceToken is not null)
{
if (!_vocab.TryGetValue(endOfSentenceToken, out int aId))
if (_vocab.TryGetValue(endOfSentenceToken, out int aId) is false && specialTokens?.TryGetValue(endOfSentenceToken, out aId) is false)
{
throw new InvalidOperationException($"The end of sentence token '{endOfSentenceToken}' was not present in the vocabulary.");
}
Expand Down Expand Up @@ -792,31 +792,30 @@ public string Decode(IEnumerable<int> ids, bool considerSpecialTokens)

ValueStringBuilder sb = new ValueStringBuilder();

bool decodeUnknownToken = _unknownTokenId.HasValue && considerSpecialTokens;

if (decodeUnknownToken)
foreach (int id in ids)
{
foreach (int id in ids)
if (_specialTokensReverse?.TryGetValue(id, out string? token) is true)
{
if (MapIdToToken(id) is string s)
if (considerSpecialTokens)
{
sb.Append(s);
sb.Append(token);
}
continue;
}
}
else
{
foreach (int id in ids)

if (id == _unknownTokenId)
{
if (id == _unknownTokenId)
if (considerSpecialTokens)
{
continue;
Debug.Assert(UnknownToken is not null);
sb.Append(UnknownToken);
}
continue;
}

if (MapIdToToken(id) is string s)
{
sb.Append(s);
}
if (MapIdToToken(id) is string s)
{
sb.Append(s);
}
}

Expand Down
60 changes: 60 additions & 0 deletions test/Microsoft.ML.Tokenizers.Tests/BpeTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -885,6 +885,66 @@ public void TestDeepSeekR1Tokenizer(string text, int[] ids, string[] tokens, (in
Assert.Equal(text, tokenizer.Decode(ids, considerSpecialTokens: false));
}

[Fact]
public void TestTokenizerWithSpecialTokens()
{
// "https://huggingface.co/openai-community/gpt2/raw/main/vocab.json";
// "https://huggingface.co/openai-community/gpt2/raw/main/merges.txt";

BpeOptions options = new BpeOptions(Path.Combine(@"Gpt-2", "vocab.json"), Path.Combine(@"Gpt-2", "merges.txt"))
{
UnknownToken = "unk",

SpecialTokens = new Dictionary<string, int> // SpecialTokens not part of the original vocab.json
{
{ "<|sos|>", 50257 },
{ "<|eos|>", 50258 }
},
BeginningOfSentenceToken = "<|sos|>",
EndOfSentenceToken = "<|eos|>"
};

BpeTokenizer bpeTokenizer = BpeTokenizer.Create(options);
Assert.True(bpeTokenizer.Vocabulary.TryGetValue(options.UnknownToken, out int unkId));

string text = "Hello world!\uD800";

var ids = bpeTokenizer.EncodeToIds(text, considerPreTokenization: false);
Assert.Equal([50257, 15496, 2954, 6894, 0, 2954, 50258], ids); // space and u+D800 couldn't be encoded and produced unk tokens
Assert.Equal(unkId, ids[ids.Count - 2]);
Assert.Equal(options.SpecialTokens["<|sos|>"], ids[0]);
Assert.Equal(options.SpecialTokens["<|eos|>"], ids[^1]);

var tokens = bpeTokenizer.EncodeToTokens(text, out _, considerPreTokenization: false).Select(t => t.Value).ToArray();
Assert.Equal(["<|sos|>", "Hello", "unk", "world", "!", "unk", "<|eos|>"], tokens);

Assert.Equal("<|sos|>Hellounkworld!unk<|eos|>", bpeTokenizer.Decode(ids));
Assert.Equal("Helloworld!", bpeTokenizer.Decode(ids, considerSpecialTokens: false));

BpeOptions options1 = new BpeOptions(options.Vocabulary)
{
// Null UnknownToken means no unknown token support
Merges = options.Merges,
SpecialTokens = options.SpecialTokens,
BeginningOfSentenceToken = options.BeginningOfSentenceToken,
EndOfSentenceToken = options.EndOfSentenceToken
};

bpeTokenizer = BpeTokenizer.Create(options1);
ids = bpeTokenizer.EncodeToIds(text, considerPreTokenization: false);

// Because Unknown is not supported in this encoding, the encoding will produce different encoding results
Assert.Equal([50257, 39, 5037, 1764, 0, 50258], ids);
Assert.Equal(options.SpecialTokens["<|sos|>"], ids[0]);
Assert.Equal(options.SpecialTokens["<|eos|>"], ids[^1]);

tokens = bpeTokenizer.EncodeToTokens(text, out _, considerPreTokenization: false).Select(t => t.Value).ToArray();
Assert.Equal(["<|sos|>", "H", "ellow", "orld", "!", "<|eos|>"], tokens);

Assert.Equal("<|sos|>Helloworld!<|eos|>", bpeTokenizer.Decode(ids));
Assert.Equal("Helloworld!", bpeTokenizer.Decode(ids, considerSpecialTokens: false));
}

private static BpeTokenizer CreateBpeTokenizerFromJson()
{
// @"https://huggingface.co/deepseek-ai/DeepSeek-R1/resolve/main/tokenizer.json?download=true"
Expand Down