Improve docstrings and type hints in scheduling_consistency_models.py (#12931)

docs: improve docstring scheduling_consistency_models.py

Author: delmalih

src/diffusers/schedulers/scheduling_consistency_models.py

@@ -83,7 +83,7 @@ def __init__(
         s_noise: float = 1.0,
         rho: float = 7.0,
         clip_denoised: bool = True,
-    ):
+    ) -> None:
         # standard deviation of the initial noise distribution
         self.init_noise_sigma = sigma_max
 
@@ -102,21 +102,29 @@ def __init__(
         self.sigmas = self.sigmas.to("cpu")  # to avoid too much CPU/GPU communication
 
     @property
-    def step_index(self):
+    def step_index(self) -> Optional[int]:
         """
         The index counter for current timestep. It will increase 1 after each scheduler step.
+
+        Returns:
+            `int` or `None`:
+                The current step index, or `None` if not yet initialized.
         """
         return self._step_index
 
     @property
-    def begin_index(self):
+    def begin_index(self) -> Optional[int]:
         """
         The index for the first timestep. It should be set from pipeline with `set_begin_index` method.
+
+        Returns:
+            `int` or `None`:
+                The begin index, or `None` if not yet set.
         """
         return self._begin_index
 
     # Copied from diffusers.schedulers.scheduling_dpmsolver_multistep.DPMSolverMultistepScheduler.set_begin_index
-    def set_begin_index(self, begin_index: int = 0):
+    def set_begin_index(self, begin_index: int = 0) -> None:
         """
         Sets the begin index for the scheduler. This function should be run from pipeline before the inference.
 
@@ -151,7 +159,7 @@ def scale_model_input(self, sample: torch.Tensor, timestep: Union[float, torch.T
         self.is_scale_input_called = True
         return sample
 
-    def sigma_to_t(self, sigmas: Union[float, np.ndarray]):
+    def sigma_to_t(self, sigmas: Union[float, np.ndarray]) -> np.ndarray:
         """
         Gets scaled timesteps from the Karras sigmas for input to the consistency model.
 
@@ -160,8 +168,8 @@ def sigma_to_t(self, sigmas: Union[float, np.ndarray]):
                 A single Karras sigma or an array of Karras sigmas.
 
         Returns:
-            `float` or `np.ndarray`:
-                A scaled input timestep or scaled input timestep array.
+            `np.ndarray`:
+                A scaled input timestep array.
         """
         if not isinstance(sigmas, np.ndarray):
             sigmas = np.array(sigmas, dtype=np.float64)
@@ -173,14 +181,14 @@ def sigma_to_t(self, sigmas: Union[float, np.ndarray]):
     def set_timesteps(
         self,
         num_inference_steps: Optional[int] = None,
-        device: Union[str, torch.device] = None,
+        device: Optional[Union[str, torch.device]] = None,
         timesteps: Optional[List[int]] = None,
-    ):
+    ) -> None:
         """
         Sets the timesteps used for the diffusion chain (to be run before inference).
 
         Args:
-            num_inference_steps (`int`):
+            num_inference_steps (`int`, *optional*):
                 The number of diffusion steps used when generating samples with a pre-trained model.
             device (`str` or `torch.device`, *optional*):
                 The device to which the timesteps should be moved to. If `None`, the timesteps are not moved.
@@ -244,9 +252,19 @@ def set_timesteps(
         self.sigmas = self.sigmas.to("cpu")  # to avoid too much CPU/GPU communication
 
     # Modified _convert_to_karras implementation that takes in ramp as argument
-    def _convert_to_karras(self, ramp):
-        """Constructs the noise schedule of Karras et al. (2022)."""
+    def _convert_to_karras(self, ramp: np.ndarray) -> np.ndarray:
+        """
+        Construct the noise schedule as proposed in [Elucidating the Design Space of Diffusion-Based Generative
+        Models](https://huggingface.co/papers/2206.00364).
 
+        Args:
+            ramp (`np.ndarray`):
+                A ramp array of values between 0 and 1 used to interpolate between sigma_min and sigma_max.
+
+        Returns:
+            `np.ndarray`:
+                The Karras sigma schedule array.
+        """
         sigma_min: float = self.config.sigma_min
         sigma_max: float = self.config.sigma_max
 
@@ -256,14 +274,25 @@ def _convert_to_karras(self, ramp):
         sigmas = (max_inv_rho + ramp * (min_inv_rho - max_inv_rho)) ** rho
         return sigmas
 
-    def get_scalings(self, sigma):
+    def get_scalings(self, sigma: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
+        """
+        Computes the scaling factors for the consistency model output.
+
+        Args:
+            sigma (`torch.Tensor`):
+                The current sigma value in the noise schedule.
+
+        Returns:
+            `Tuple[torch.Tensor, torch.Tensor]`:
+                A tuple containing `c_skip` (scaling for the input sample) and `c_out` (scaling for the model output).
+        """
         sigma_data = self.config.sigma_data
 
         c_skip = sigma_data**2 / (sigma**2 + sigma_data**2)
         c_out = sigma * sigma_data / (sigma**2 + sigma_data**2) ** 0.5
         return c_skip, c_out
 
-    def get_scalings_for_boundary_condition(self, sigma):
+    def get_scalings_for_boundary_condition(self, sigma: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
         """
         Gets the scalings used in the consistency model parameterization (from Appendix C of the
         [paper](https://huggingface.co/papers/2303.01469)) to enforce boundary condition.
@@ -275,7 +304,7 @@ def get_scalings_for_boundary_condition(self, sigma):
                 The current sigma in the Karras sigma schedule.
 
         Returns:
-            `tuple`:
+            `Tuple[torch.Tensor, torch.Tensor]`:
                 A two-element tuple where `c_skip` (which weights the current sample) is the first element and `c_out`
                 (which weights the consistency model output) is the second element.
         """
@@ -348,13 +377,13 @@ def step(
         Args:
             model_output (`torch.Tensor`):
                 The direct output from the learned diffusion model.
-            timestep (`float`):
+            timestep (`float` or `torch.Tensor`):
                 The current timestep in the diffusion chain.
             sample (`torch.Tensor`):
                 A current instance of a sample created by the diffusion process.
             generator (`torch.Generator`, *optional*):
                 A random number generator.
-            return_dict (`bool`, *optional*, defaults to `True`):
+            return_dict (`bool`, defaults to `True`):
                 Whether or not to return a
                 [`~schedulers.scheduling_consistency_models.CMStochasticIterativeSchedulerOutput`] or `tuple`.
 
@@ -406,7 +435,10 @@ def step(
         # Noise is not used for onestep sampling.
         if len(self.timesteps) > 1:
             noise = randn_tensor(
-                model_output.shape, dtype=model_output.dtype, device=model_output.device, generator=generator
+                model_output.shape,
+                dtype=model_output.dtype,
+                device=model_output.device,
+                generator=generator,
             )
         else:
             noise = torch.zeros_like(model_output)
@@ -475,5 +507,12 @@ def add_noise(
         noisy_samples = original_samples + noise * sigma
         return noisy_samples
 
-    def __len__(self):
+    def __len__(self) -> int:
+        """
+        Returns the number of training timesteps.
+
+        Returns:
+            `int`:
+                The number of training timesteps configured for the scheduler.
+        """
         return self.config.num_train_timesteps