Move generation of sampling params (#1340)

This PR addresses #1335 
I have kept the `SamplingParameters` in `outlines/generate/api.py` cause
its imported at many places and may break examples ig.
Would you want to change that @dgerlanc ??
Otherwise if this looks good, I can make docs changes if needd, lmk.

outlines/generate/api.py

@@ -4,7 +4,6 @@
 from typing import TYPE_CHECKING, Any, Iterator, List, Optional, Union
 
 from outlines.generate.generator import sequence_generator
-from outlines.samplers import BeamSearchSampler, GreedySampler, MultinomialSampler
 
 if TYPE_CHECKING:
     import torch
@@ -353,11 +352,13 @@ def token_generator() -> Iterator[Union[List[str], str, List[List[str]]]]:
                     ]
 
                     generated_sequences = [
-                        self.format_sequence(
-                            self.strip_stop_sequences(sequence, stop_sequences)
+                        (
+                            self.format_sequence(
+                                self.strip_stop_sequences(sequence, stop_sequences)
+                            )
+                            if stop
+                            else sequence
                         )
-                        if stop
-                        else sequence
                         for sequence, stop in zip(
                             generated_sequences, is_stop_at_reached
                         )
@@ -428,22 +429,7 @@ def __init__(self, model, logits_processor, sampler):
         self.model = model
         self.logits_processor = logits_processor
 
-        if isinstance(sampler, MultinomialSampler):
-            self.sampling_params = SamplingParameters(
-                "multinomial",
-                sampler.samples,
-                sampler.top_p,
-                sampler.top_k,
-                sampler.temperature,
-            )
-        elif isinstance(sampler, GreedySampler):
-            self.sampling_params = SamplingParameters(
-                "greedy", sampler.samples, None, None, 0.0
-            )
-        elif isinstance(sampler, BeamSearchSampler):
-            self.sampling_params = SamplingParameters(
-                "beam_search", sampler.samples, None, None, 1.0
-            )
+        self.sampling_params = sampler.sampling_params
 
     def prepare_generation_parameters(
         self,

outlines/samplers.py

@@ -1,4 +1,5 @@
 import math
+from dataclasses import dataclass
 from typing import TYPE_CHECKING, Callable, Optional, Protocol, Tuple
 
 if TYPE_CHECKING:
@@ -17,6 +18,17 @@ def __call__(
         ...
 
 
+@dataclass(frozen=True)
+class SamplingParameters:
+    """Sampling parameters available in Outlines."""
+
+    sampler: str
+    num_samples: int = 1
+    top_p: Optional[float] = None
+    top_k: Optional[int] = None
+    temperature: Optional[float] = None
+
+
 class GreedySampler:
     """Greedy Sampling algorithm.
 
@@ -76,6 +88,10 @@ def __call__(
 
         return next_token_ids, ancestors, weights
 
+    @property
+    def sampling_params(self):
+        return SamplingParameters("greedy", self.samples, None, None, 0.0)
+
 
 greedy = GreedySampler
 
@@ -161,6 +177,16 @@ def __call__(
 
         return next_token_ids, ancestors, weights
 
+    @property
+    def sampling_params(self):
+        return SamplingParameters(
+            "multinomial",
+            self.samples,
+            self.top_p,
+            self.top_k,
+            self.temperature,
+        )
+
 
 multinomial = MultinomialSampler
 
@@ -320,5 +346,9 @@ def __call__(
 
         return next_token_ids, ancestors, weights
 
+    @property
+    def sampling_params(self):
+        return SamplingParameters("beam_search", self.samples, None, None, 1.0)
+
 
 beam_search = BeamSearchSampler

tests/test_samplers.py

@@ -47,6 +47,13 @@ def test_greedy():
     assert ancestors.equal(torch.tensor([0, 1]))
     assert weights.equal(torch.tensor([logprobs[0, 0], logprobs[1, 2]]))
 
+    params = sampler.sampling_params
+    assert params.sampler == "greedy"
+    assert params.num_samples == 1
+    assert params.top_p is None
+    assert params.top_k is None
+    assert params.temperature == 0.0
+
 
 def test_multinomial():
     rng = torch.Generator()
@@ -72,6 +79,14 @@ def test_multinomial():
     assert ancestors.equal(torch.tensor([0, 1]))
     assert weights.equal(torch.tensor([logprobs[0, 0], logprobs[1, 2]]))
 
+    sampler = MultinomialSampler(samples=5, top_k=10, top_p=0.9, temperature=0.8)
+    params = sampler.sampling_params
+    assert params.sampler == "multinomial"
+    assert params.num_samples == 5
+    assert params.top_p == 0.9
+    assert params.top_k == 10
+    assert params.temperature == 0.8
+
 
 def test_multinomial_init():
     sampler = MultinomialSampler()
@@ -252,3 +267,11 @@ def test_beam_search():
             ]
         )
     )
+
+    sampler = BeamSearchSampler(beams=3)
+    params = sampler.sampling_params
+    assert params.sampler == "beam_search"
+    assert params.num_samples == 3
+    assert params.top_p is None
+    assert params.top_k is None
+    assert params.temperature == 1.0