diff --git a/src/diffusers/schedulers/scheduling_ddim.py b/src/diffusers/schedulers/scheduling_ddim.py
index 5ee0d084f0..c63f1f4c16 100644
--- a/src/diffusers/schedulers/scheduling_ddim.py
+++ b/src/diffusers/schedulers/scheduling_ddim.py
@@ -17,7 +17,7 @@
 
 import math
 from dataclasses import dataclass
-from typing import List, Optional, Tuple, Union
+from typing import List, Literal, Optional, Tuple, Union
 
 import numpy as np
 import torch
@@ -92,11 +92,10 @@ def betas_for_alpha_bar(
     return torch.tensor(betas, dtype=torch.float32)
 
 
-def rescale_zero_terminal_snr(betas):
+def rescale_zero_terminal_snr(betas: torch.Tensor) -> torch.Tensor:
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
@@ -143,9 +142,9 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
             The starting `beta` value of inference.
         beta_end (`float`, defaults to 0.02):
             The final `beta` value.
-        beta_schedule (`str`, defaults to `"linear"`):
-            The beta schedule, a mapping from a beta range to a sequence of betas for stepping the model. Choose from
-            `linear`, `scaled_linear`, or `squaredcos_cap_v2`.
+        beta_schedule (`Literal["linear", "scaled_linear", "squaredcos_cap_v2"]`, defaults to `"linear"`):
+            The beta schedule, a mapping from a beta range to a sequence of betas for stepping the model. Must be one
+            of `"linear"`, `"scaled_linear"`, or `"squaredcos_cap_v2"`.
         trained_betas (`np.ndarray`, *optional*):
             Pass an array of betas directly to the constructor to bypass `beta_start` and `beta_end`.
         clip_sample (`bool`, defaults to `True`):
@@ -158,10 +157,10 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
             otherwise it uses the alpha value at step 0.
         steps_offset (`int`, defaults to 0):
             An offset added to the inference steps, as required by some model families.
-        prediction_type (`str`, defaults to `epsilon`, *optional*):
-            Prediction type of the scheduler function; can be `epsilon` (predicts the noise of the diffusion process),
-            `sample` (directly predicts the noisy sample`) or `v_prediction` (see section 2.4 of [Imagen
-            Video](https://imagen.research.google/video/paper.pdf) paper).
+        prediction_type (`Literal["epsilon", "sample", "v_prediction"]`, defaults to `"epsilon"`):
+            Prediction type of the scheduler function. Must be one of `"epsilon"` (predicts the noise of the diffusion
+            process), `"sample"` (directly predicts the noisy sample), or `"v_prediction"` (see section 2.4 of [Imagen
+            Video](https://huggingface.co/papers/2210.02303) paper).
         thresholding (`bool`, defaults to `False`):
             Whether to use the "dynamic thresholding" method. This is unsuitable for latent-space diffusion models such
             as Stable Diffusion.
@@ -169,9 +168,10 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
             The ratio for the dynamic thresholding method. Valid only when `thresholding=True`.
         sample_max_value (`float`, defaults to 1.0):
             The threshold value for dynamic thresholding. Valid only when `thresholding=True`.
-        timestep_spacing (`str`, defaults to `"leading"`):
-            The way the timesteps should be scaled. Refer to Table 2 of the [Common Diffusion Noise Schedules and
-            Sample Steps are Flawed](https://huggingface.co/papers/2305.08891) for more information.
+        timestep_spacing (`Literal["leading", "trailing", "linspace"]`, defaults to `"leading"`):
+            The way the timesteps should be scaled. Must be one of `"leading"`, `"trailing"`, or `"linspace"`. Refer to
+            Table 2 of the [Common Diffusion Noise Schedules and Sample Steps are
+            Flawed](https://huggingface.co/papers/2305.08891) for more information.
         rescale_betas_zero_snr (`bool`, defaults to `False`):
             Whether to rescale the betas to have zero terminal SNR. This enables the model to generate very bright and
             dark samples instead of limiting it to samples with medium brightness. Loosely related to
@@ -187,17 +187,17 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         num_train_timesteps: int = 1000,
         beta_start: float = 0.0001,
         beta_end: float = 0.02,
-        beta_schedule: str = "linear",
+        beta_schedule: Literal["linear", "scaled_linear", "squaredcos_cap_v2"] = "linear",
         trained_betas: Optional[Union[np.ndarray, List[float]]] = None,
         clip_sample: bool = True,
         set_alpha_to_one: bool = True,
         steps_offset: int = 0,
-        prediction_type: str = "epsilon",
+        prediction_type: Literal["epsilon", "sample", "v_prediction"] = "epsilon",
         thresholding: bool = False,
         dynamic_thresholding_ratio: float = 0.995,
         clip_sample_range: float = 1.0,
         sample_max_value: float = 1.0,
-        timestep_spacing: str = "leading",
+        timestep_spacing: Literal["leading", "trailing", "linspace"] = "leading",
         rescale_betas_zero_snr: bool = False,
     ):
         if trained_betas is not None:
@@ -250,7 +250,25 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         """
         return sample
 
-    def _get_variance(self, timestep, prev_timestep):
+    def _get_variance(self, timestep: int, prev_timestep: int) -> torch.Tensor:
+        """
+        Computes the variance of the noise added at a given diffusion step.
+
+        For a given `timestep` and its previous step, this method calculates the variance as defined in DDIM/DDPM
+        literature:
+            var_t = (beta_prod_t_prev / beta_prod_t) * (1 - alpha_prod_t / alpha_prod_t_prev)
+        where alpha_prod and beta_prod are cumulative products of alphas and betas, respectively.
+
+        Args:
+            timestep (`int`):
+                The current timestep in the diffusion process.
+            prev_timestep (`int`):
+                The previous timestep in the diffusion process. If negative, uses `final_alpha_cumprod`.
+
+        Returns:
+            `torch.Tensor`:
+                The variance for the current timestep.
+        """
         alpha_prod_t = self.alphas_cumprod[timestep]
         alpha_prod_t_prev = self.alphas_cumprod[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
         beta_prod_t = 1 - alpha_prod_t
@@ -294,13 +312,18 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
 
         return sample
 
-    def set_timesteps(self, num_inference_steps: int, device: Union[str, torch.device] = None):
+    def set_timesteps(self, num_inference_steps: int, device: Union[str, torch.device] = None) -> None:
         """
         Sets the discrete timesteps used for the diffusion chain (to be run before inference).
 
         Args:
             num_inference_steps (`int`):
                 The number of diffusion steps used when generating samples with a pre-trained model.
+            device (`Union[str, torch.device]`, *optional*):
+                The device to use for the timesteps.
+
+        Raises:
+            ValueError: If `num_inference_steps` is larger than `self.config.num_train_timesteps`.
         """
 
         if num_inference_steps > self.config.num_train_timesteps:
@@ -346,7 +369,7 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         sample: torch.Tensor,
         eta: float = 0.0,
         use_clipped_model_output: bool = False,
-        generator=None,
+        generator: Optional[torch.Generator] = None,
         variance_noise: Optional[torch.Tensor] = None,
         return_dict: bool = True,
     ) -> Union[DDIMSchedulerOutput, Tuple]:
@@ -357,20 +380,21 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         Args:
             model_output (`torch.Tensor`):
                 The direct output from learned diffusion model.
-            timestep (`float`):
+            timestep (`int`):
                 The current discrete timestep in the diffusion chain.
             sample (`torch.Tensor`):
                 A current instance of a sample created by the diffusion process.
-            eta (`float`):
-                The weight of noise for added noise in diffusion step.
-            use_clipped_model_output (`bool`, defaults to `False`):
+            eta (`float`, *optional*, defaults to 0.0):
+                The weight of noise for added noise in diffusion step. A value of 0 corresponds to DDIM (deterministic)
+                and 1 corresponds to DDPM (fully stochastic).
+            use_clipped_model_output (`bool`, *optional*, defaults to `False`):
                 If `True`, computes "corrected" `model_output` from the clipped predicted original sample. Necessary
                 because predicted original sample is clipped to [-1, 1] when `self.config.clip_sample` is `True`. If no
                 clipping has happened, "corrected" `model_output` would coincide with the one provided as input and
                 `use_clipped_model_output` has no effect.
             generator (`torch.Generator`, *optional*):
-                A random number generator.
-            variance_noise (`torch.Tensor`):
+                A random number generator for reproducible sampling.
+            variance_noise (`torch.Tensor`, *optional*):
                 Alternative to generating noise with `generator` by directly providing the noise for the variance
                 itself. Useful for methods such as [`CycleDiffusion`].
             return_dict (`bool`, *optional*, defaults to `True`):
@@ -517,5 +541,5 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         velocity = sqrt_alpha_prod * noise - sqrt_one_minus_alpha_prod * sample
         return velocity
 
-    def __len__(self):
+    def __len__(self) -> int:
         return self.config.num_train_timesteps
diff --git a/src/diffusers/schedulers/scheduling_ddim_inverse.py b/src/diffusers/schedulers/scheduling_ddim_inverse.py
index 49dba840d0..d13ac60680 100644
--- a/src/diffusers/schedulers/scheduling_ddim_inverse.py
+++ b/src/diffusers/schedulers/scheduling_ddim_inverse.py
@@ -95,7 +95,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_ddim_parallel.py b/src/diffusers/schedulers/scheduling_ddim_parallel.py
index 7c3f03a8db..deffdb4ff7 100644
--- a/src/diffusers/schedulers/scheduling_ddim_parallel.py
+++ b/src/diffusers/schedulers/scheduling_ddim_parallel.py
@@ -17,7 +17,7 @@
 
 import math
 from dataclasses import dataclass
-from typing import List, Optional, Tuple, Union
+from typing import List, Literal, Optional, Tuple, Union
 
 import numpy as np
 import torch
@@ -97,7 +97,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
@@ -194,17 +193,17 @@ class DDIMParallelScheduler(SchedulerMixin, ConfigMixin):
         num_train_timesteps: int = 1000,
         beta_start: float = 0.0001,
         beta_end: float = 0.02,
-        beta_schedule: str = "linear",
+        beta_schedule: Literal["linear", "scaled_linear", "squaredcos_cap_v2"] = "linear",
         trained_betas: Optional[Union[np.ndarray, List[float]]] = None,
         clip_sample: bool = True,
         set_alpha_to_one: bool = True,
         steps_offset: int = 0,
-        prediction_type: str = "epsilon",
+        prediction_type: Literal["epsilon", "sample", "v_prediction"] = "epsilon",
         thresholding: bool = False,
         dynamic_thresholding_ratio: float = 0.995,
         clip_sample_range: float = 1.0,
         sample_max_value: float = 1.0,
-        timestep_spacing: str = "leading",
+        timestep_spacing: Literal["leading", "trailing", "linspace"] = "leading",
         rescale_betas_zero_snr: bool = False,
     ):
         if trained_betas is not None:
@@ -324,6 +323,11 @@ class DDIMParallelScheduler(SchedulerMixin, ConfigMixin):
         Args:
             num_inference_steps (`int`):
                 The number of diffusion steps used when generating samples with a pre-trained model.
+            device (`Union[str, torch.device]`, *optional*):
+                The device to use for the timesteps.
+
+        Raises:
+            ValueError: If `num_inference_steps` is larger than `self.config.num_train_timesteps`.
         """
 
         if num_inference_steps > self.config.num_train_timesteps:
diff --git a/src/diffusers/schedulers/scheduling_ddpm.py b/src/diffusers/schedulers/scheduling_ddpm.py
index 0fab6d910a..b59fae0664 100644
--- a/src/diffusers/schedulers/scheduling_ddpm.py
+++ b/src/diffusers/schedulers/scheduling_ddpm.py
@@ -94,7 +94,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_ddpm_parallel.py b/src/diffusers/schedulers/scheduling_ddpm_parallel.py
index ec741f9ecb..c78bfe290f 100644
--- a/src/diffusers/schedulers/scheduling_ddpm_parallel.py
+++ b/src/diffusers/schedulers/scheduling_ddpm_parallel.py
@@ -96,7 +96,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_dpmsolver_multistep.py b/src/diffusers/schedulers/scheduling_dpmsolver_multistep.py
index 8b523cd13f..0560a03032 100644
--- a/src/diffusers/schedulers/scheduling_dpmsolver_multistep.py
+++ b/src/diffusers/schedulers/scheduling_dpmsolver_multistep.py
@@ -80,7 +80,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_euler_ancestral_discrete.py b/src/diffusers/schedulers/scheduling_euler_ancestral_discrete.py
index 9cdaa2c5e1..38ad401edc 100644
--- a/src/diffusers/schedulers/scheduling_euler_ancestral_discrete.py
+++ b/src/diffusers/schedulers/scheduling_euler_ancestral_discrete.py
@@ -97,7 +97,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_euler_discrete.py b/src/diffusers/schedulers/scheduling_euler_discrete.py
index f58d918dbf..59199bf710 100644
--- a/src/diffusers/schedulers/scheduling_euler_discrete.py
+++ b/src/diffusers/schedulers/scheduling_euler_discrete.py
@@ -100,7 +100,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_lcm.py b/src/diffusers/schedulers/scheduling_lcm.py
index cd7a29fe67..8a0fd48050 100644
--- a/src/diffusers/schedulers/scheduling_lcm.py
+++ b/src/diffusers/schedulers/scheduling_lcm.py
@@ -99,7 +99,6 @@ def rescale_zero_terminal_snr(betas: torch.Tensor) -> torch.Tensor:
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
diff --git a/src/diffusers/schedulers/scheduling_tcd.py b/src/diffusers/schedulers/scheduling_tcd.py
index 3fd5c341ec..ce7d1d5316 100644
--- a/src/diffusers/schedulers/scheduling_tcd.py
+++ b/src/diffusers/schedulers/scheduling_tcd.py
@@ -98,7 +98,6 @@ def rescale_zero_terminal_snr(betas: torch.Tensor) -> torch.Tensor:
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.
@@ -316,6 +315,24 @@ class TCDScheduler(SchedulerMixin, ConfigMixin):
 
     # Copied from diffusers.schedulers.scheduling_ddim.DDIMScheduler._get_variance
     def _get_variance(self, timestep, prev_timestep):
+        """
+        Computes the variance of the noise added at a given diffusion step.
+
+        For a given `timestep` and its previous step, this method calculates the variance as defined in DDIM/DDPM
+        literature:
+            var_t = (beta_prod_t_prev / beta_prod_t) * (1 - alpha_prod_t / alpha_prod_t_prev)
+        where alpha_prod and beta_prod are cumulative products of alphas and betas, respectively.
+
+        Args:
+            timestep (`int`):
+                The current timestep in the diffusion process.
+            prev_timestep (`int`):
+                The previous timestep in the diffusion process. If negative, uses `final_alpha_cumprod`.
+
+        Returns:
+            `torch.Tensor`:
+                The variance for the current timestep.
+        """
         alpha_prod_t = self.alphas_cumprod[timestep]
         alpha_prod_t_prev = self.alphas_cumprod[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
         beta_prod_t = 1 - alpha_prod_t
diff --git a/src/diffusers/schedulers/scheduling_unipc_multistep.py b/src/diffusers/schedulers/scheduling_unipc_multistep.py
index 162a34bd27..a596fef245 100644
--- a/src/diffusers/schedulers/scheduling_unipc_multistep.py
+++ b/src/diffusers/schedulers/scheduling_unipc_multistep.py
@@ -80,7 +80,6 @@ def rescale_zero_terminal_snr(betas):
     """
     Rescales betas to have zero terminal SNR Based on https://huggingface.co/papers/2305.08891 (Algorithm 1)
 
-
     Args:
         betas (`torch.Tensor`):
             the betas that the scheduler is being initialized with.