Enable dropout = 0.0 as an equivalent to none in BPE (#1550)

* enable dropout = 0.0

* typo

* lint

* formatter

* enable dropout = 0.0

* formatter

bindings/python/tests/bindings/test_models.py

@@ -69,6 +69,10 @@ def test_can_modify(self):
         model.byte_fallback = True
         assert model.byte_fallback == True
 
+    def test_dropout_zero(self):
+        model = BPE(dropout=0.0)
+        assert model.dropout == 0.0
+
 
 class TestWordPiece:
     def test_instantiate(self, bert_files):

tokenizers/src/models/bpe/mod.rs

@@ -31,7 +31,7 @@ pub enum Error {
     #[error("Unk token `{0}` not found in the vocabulary")]
     UnkTokenOutOfVocabulary(String),
     /// Dropout not between 0 and 1.
-    #[error("Dropout should be between 0 and 1")]
+    #[error("Dropout should be between 0 and 1, inclusive")]
     InvalidDropout,
 }
 

tokenizers/src/models/bpe/model.rs

@@ -136,7 +136,7 @@ impl BpeBuilder {
     pub fn build(mut self) -> Result<BPE> {
         // Validate dropout.
         if let Some(p) = self.config.dropout {
-            if p <= 0.0 || p > 1.0 {
+            if !(0.0..=1.0).contains(&p) {
                 return Err(Error::InvalidDropout.into());
             }
         }
@@ -214,7 +214,7 @@ pub struct BPE {
     pub(crate) merges: MergeMap,
     /// Contains the cache for optimizing the encoding step.
     cache: Option<Cache<String, Word>>,
-    /// Dropout probability for merges. 0 = no dropout is the default. At 1.0, tokenization will
+    /// Dropout probability for merges. 0.0 = no dropout is the default. At 1.0, tokenization will
     /// perform no merges, so the result will just be characters.
     pub dropout: Option<f32>,
     /// The unknown token to be used when we encounter an unknown char
@@ -493,7 +493,7 @@ impl Model for BPE {
             return Ok(vec![]);
         }
 
-        if self.dropout.is_none() {
+        if self.dropout.is_none() || self.dropout == Some(0.0) {
             self.tokenize_with_cache(sequence)
         } else {
             let word = self.merge_word(sequence)?;
@@ -685,6 +685,11 @@ mod tests {
         let tokens = bpe.tokenize("unrelated").unwrap();
         assert_eq!(tokens, vec![Token::new(15u32, "unrelated".into(), (0, 9))]);
 
+        // With dropout = 0.0 (equivalent to dropout == none)
+        bpe.dropout = Some(0.0);
+        let tokens = bpe.tokenize("unrelated").unwrap();
+        assert_eq!(tokens, vec![Token::new(15u32, "unrelated".into(), (0, 9))]);
+
         // Now set dropout to 1.0. Result should be no merges performed.
         bpe.dropout = Some(1.0);
         let tokens = bpe.tokenize("unrelated").unwrap();
@@ -739,6 +744,13 @@ mod tests {
         assert_eq!(bpe.vocab.get("ab").unwrap(), &3u32);
     }
 
+    #[test]
+    // Ensure BPEBuilder with dropout = 0.0 doesn't error
+    fn test_bpe_with_dropout_0() {
+        let bpe = BPE::builder().dropout(0.0).build().unwrap();
+        assert_eq!(bpe.dropout, Some(0.0));
+    }
+
     #[test]
     // Ensure `BPE::from_file` works as expected.
     fn test_bpe_with_continuing_subword_prefix() {

tokenizers/tests/serialization.rs

@@ -229,6 +229,21 @@ fn tokenizer() {
     assert_eq!(serde_json::to_string(&de).unwrap(), ser);
 }
 
+#[test]
+fn bpe_with_dropout_serde() {
+    let mut bpe = BPE::default();
+    bpe.dropout = Some(0.1);
+    let ser = serde_json::to_string(&bpe).unwrap();
+    let de = serde_json::from_str(&ser).unwrap();
+    assert_eq!(bpe, de);
+
+    // set dropout to 0.0 (which is analogous to None) and reserialize
+    bpe.dropout = Some(0.0);
+    let ser = serde_json::to_string(&bpe).unwrap();
+    let de = serde_json::from_str(&ser).unwrap();
+    assert_eq!(bpe, de);
+}
+
 #[test]
 fn test_deserialize_long_file() {
     let _tokenizer = Tokenizer::from_file("data/albert-base-v1-tokenizer.json").unwrap();