diff --git a/.github/workflows/pypi-publish.yml b/.github/workflows/pypi-publish.yml
index 91ce4a6..7b591a2 100644
--- a/.github/workflows/pypi-publish.yml
+++ b/.github/workflows/pypi-publish.yml
@@ -48,4 +48,4 @@ jobs:
       uses: pypa/gh-action-pypi-publish@27b31702a0e7fc50959f5ad993c78deac1bdfc29
       with:
         user: __token__
-        password: ${{ secrets.PYPI_PASSWORD }}
\ No newline at end of file
+        password: ${{ secrets.PYPI_PASSWORD }}
diff --git a/.github/workflows/pypi-test.yml b/.github/workflows/pypi-test.yml
index d3a319d..9dc019a 100644
--- a/.github/workflows/pypi-test.yml
+++ b/.github/workflows/pypi-test.yml
@@ -1,7 +1,7 @@
 # This workflow will install Python dependencies, run tests and lint with a single version of Python
 # For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
 
-name: test the library
+name: Test the library
 
 on:
   push:
@@ -13,13 +13,18 @@ jobs:
   build:
 
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [ '3.8', '3.9', '3.10', '3.11', '3.12' ]
 
+    name: Python ${{ matrix.python-version }}
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.9
+    - name: Setup Python
       uses: actions/setup-python@v2
       with:
-        python-version: 3.9
+        python-version: ${{ matrix.python-version }}
+        cache: 'pip'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
@@ -32,4 +37,4 @@ jobs:
     #     # flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Test with tox
       run: |
-        tox
\ No newline at end of file
+        tox
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..df3a2f4
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,52 @@
+exclude: '^docs/conf.py'
+
+repos:
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v4.5.0
+  hooks:
+  - id: trailing-whitespace
+  - id: check-added-large-files
+  - id: check-ast
+  - id: check-json
+  - id: check-merge-conflict
+  - id: check-xml
+  - id: check-yaml
+  - id: debug-statements
+  - id: end-of-file-fixer
+  - id: requirements-txt-fixer
+  - id: mixed-line-ending
+    args: ['--fix=auto']  # replace 'auto' with 'lf' to enforce Linux/Mac line endings or 'crlf' for Windows
+
+- repo: https://github.com/PyCQA/docformatter
+  rev: v1.7.5
+  hooks:
+    - id: docformatter
+      additional_dependencies: [tomli]
+      args: [--in-place, --wrap-descriptions=120, --wrap-summaries=120]
+      # --config, ./pyproject.toml
+
+- repo: https://github.com/psf/black
+  rev: 23.12.1
+  hooks:
+  - id: black
+    language_version: python3
+
+- repo: https://github.com/astral-sh/ruff-pre-commit
+  # Ruff version.
+  rev: v0.1.9
+  hooks:
+    - id: ruff
+      args: [--fix, --exit-non-zero-on-fix]
+
+## If like to embrace black styles even in the docs:
+# - repo: https://github.com/asottile/blacken-docs
+#   rev: v1.13.0
+#   hooks:
+#   - id: blacken-docs
+#     additional_dependencies: [black]
+
+## Check for misspells in documentation files:
+# - repo: https://github.com/codespell-project/codespell
+#   rev: v2.2.5
+#   hooks:
+#   - id: codespell
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d203ca4..941c1af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,11 +1,11 @@
 # Changelog
 
 
-## Version 0.2.0 
+## Version 0.2.0
 - Support multi apply
 
 ## Version 0.1 (development)
 
 - first release
-- performs some basic operations over numpy or scipy matrices. 
+- performs some basic operations over numpy or scipy matrices.
 - provides apply method so user can extend the underlying logic to any function
diff --git a/docs/conf.py b/docs/conf.py
index 862e58a..7cf736a 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -169,6 +169,15 @@ def setup(app):
 # If this is True, todo emits a warning for each TODO entries. The default is False.
 todo_emit_warnings = True
 
+autodoc_default_options = {
+      'special-members': True,
+      'undoc-members': False,
+      'exclude-members': '__weakref__, __dict__, __str__, __module__, __init__'
+  }
+
+autosummary_generate = True
+autosummary_imported_members = True
+
 
 # -- Options for HTML output -------------------------------------------------
 
diff --git a/docs/requirements.txt b/docs/requirements.txt
index 2662cf2..0aec8ef 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,7 +1,7 @@
+furo
 # Requirements file for ReadTheDocs, check .readthedocs.yml.
 # To build the module reference correctly, make sure every external package
 # under `install_requires` in `setup.cfg` is also listed here!
 # sphinx_rtd_theme
 recommonmark
 sphinx>=3.2.1
-furo
\ No newline at end of file
diff --git a/docs/tutorial.md b/docs/tutorial.md
index 1bca5f9..39f797f 100644
--- a/docs/tutorial.md
+++ b/docs/tutorial.md
@@ -50,7 +50,7 @@ apply(nz_func, mat, axis=1)
 
 ## Multiple functions
 
-`mopsy` also supports applying multiple functions at the same time. 
+`mopsy` also supports applying multiple functions at the same time.
 
 ```python
 from mopsy import multi_apply
@@ -73,4 +73,4 @@ tmat_wrow = append_row(mat, np.array([0, 0, 0, 0, 0]))
 tmat_wcol = append_col(mat, np.array([[0], [0], [0], [0], [0]]))
 ```
 
-That's all for today! 
\ No newline at end of file
+That's all for today!
diff --git a/pyproject.toml b/pyproject.toml
index 2c63dbb..a7cea75 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -6,3 +6,18 @@ build-backend = "setuptools.build_meta"
 [tool.setuptools_scm]
 # See configuration details in https://github.com/pypa/setuptools_scm
 version_scheme = "no-guess-dev"
+
+[tool.ruff]
+line-length = 120
+src = ["src"]
+exclude = ["tests"]
+extend-ignore = ["F821"]
+
+[tool.ruff.pydocstyle]
+convention = "google"
+
+[tool.ruff.per-file-ignores]
+"__init__.py" = ["E402", "F401"]
+
+[tool.black]
+force-exclude = "__init__.py"
diff --git a/setup.py b/setup.py
index 2cbcbdb..eb4e889 100644
--- a/setup.py
+++ b/setup.py
@@ -1,10 +1,8 @@
-"""
-    Setup file for mopsy.
-    Use setup.cfg to configure your project.
+"""Setup file for mopsy. Use setup.cfg to configure your project.
 
-    This file was generated with PyScaffold 4.1.1.
-    PyScaffold helps you to put up the scaffold of your new Python project.
-    Learn more under: https://pyscaffold.org/
+This file was generated with PyScaffold 4.1.1.
+PyScaffold helps you to put up the scaffold of your new Python project.
+Learn more under: https://pyscaffold.org/
 """
 from setuptools import setup
 
diff --git a/src/mopsy/__init__.py b/src/mopsy/__init__.py
index 938f2dc..dabba4e 100644
--- a/src/mopsy/__init__.py
+++ b/src/mopsy/__init__.py
@@ -21,5 +21,5 @@
 finally:
     del version, PackageNotFoundError
 
-from .helpers import *
-from .adders import *
+from .helpers import *  # noqa: F403
+from .adders import *  # noqa: F403
diff --git a/src/mopsy/adders.py b/src/mopsy/adders.py
index 68ec930..fbdb260 100644
--- a/src/mopsy/adders.py
+++ b/src/mopsy/adders.py
@@ -1,10 +1,10 @@
-from .sops import Sops
-from .checkutils import check_axis
-
 from typing import Union
 
-import scipy as sp
 import numpy as np
+import scipy as sp
+
+from .checkutils import check_axis
+from .sops import Sops
 
 __author__ = "jkanche"
 __copyright__ = "jkanche"
@@ -14,56 +14,69 @@
 def append_row(
     mat: sp.sparse.spmatrix, row: Union[sp.sparse.spmatrix, np.ndarray]
 ) -> sp.sparse.spmatrix:
-    """A generic append function for sparse matrices
+    """A generic append function for sparse matrices.
 
     Args:
-        mat (scipy.sparse.spmatrix): sparse matrix
-        row (Union[sp.sparse.spmatrix, np.ndarray]): rows to append
+        mat:
+            Sparse matrix.
+        row:
+            Rows to append.
 
     Raises:
-        TypeError: if axis is neither 0 nor 1
+        TypeError:
+            If axis is neither 0 nor 1.
 
     Returns:
-        scipy.sparse.spmatrix: new matrix
+        A new sparse matrix, usually the same type as the input matrix.
     """
-    return sparse_append(mat=mat, rowOrCols=row, axis=0)
+    return sparse_append(mat=mat, row_or_column=row, axis=0)
 
 
 def append_col(
     mat: sp.sparse.spmatrix, col: Union[sp.sparse.spmatrix, np.ndarray]
 ) -> sp.sparse.spmatrix:
-    """A generic append function for sparse matrices
+    """A generic append function for sparse matrices.
 
     Args:
-        mat (scipy.sparse.spmatrix): sparse matrix
-        col (Union[sp.sparse.spmatrix, np.ndarray]): columns to append
+        mat:
+            Sparse matrix.
+
+        col:
+            Columns to append.
 
     Raises:
-        TypeError: if axis is neither 0 nor 1
+        TypeError:
+            If axis is neither 0 nor 1.
 
     Returns:
-        scipy.sparse.spmatrix: new matrix
+        A new sparse matrix, usually the same type as the input matrix.
     """
-    return sparse_append(mat=mat, rowOrCols=col, axis=1)
+    return sparse_append(mat=mat, row_or_column=col, axis=1)
 
 
 def sparse_append(
     mat: sp.sparse.spmatrix,
-    rowOrCols: Union[sp.sparse.spmatrix, np.ndarray],
+    row_or_column: Union[sp.sparse.spmatrix, np.ndarray],
     axis: Union[int, bool],
 ) -> sp.sparse.spmatrix:
-    """A generic append function for sparse matrices
+    """A generic append function for sparse matrices.
 
     Args:
-        mat (scipy.sparse.spmatrix): sparse matrix
-        rowOrCols (Union[sp.sparse.spmatrix, np.ndarray]): rows to append
-        axis (Union[int, bool]): 0 for rows, 1 for columns.
+        mat:
+            Sparse matrix.
+
+        row_or_column:
+            Rows or columns to append.
+
+        axis:
+            0 for rows, 1 for columns.
 
     Raises:
-        TypeError: if axis is neither 0 nor 1
+        TypeError:
+            If axis is neither 0 nor 1.
 
     Returns:
-        scipy.sparse.spmatrix: new matrix
+        A new sparse matrix, usually the same type as the input matrix.
     """
 
     if not isinstance(mat, sp.sparse.spmatrix):
@@ -75,19 +88,19 @@ def sparse_append(
 
     new_mat = None
     if axis == 0:
-        if mat.shape[0] != rowOrCols.shape[0]:
+        if mat.shape[0] != row_or_column.shape[0]:
             raise TypeError(
-                f"matrix and new row do not have the same length. matrix: {mat.shape[0]}, row: {row.shape[0]}"
+                "Matrix and new row do not have the same shape along the first dimension."
             )
 
-        new_mat = sp.sparse.vstack([mat, rowOrCols])
+        new_mat = sp.sparse.vstack([mat, row_or_column])
     else:
-        if mat.shape[1] != rowOrCols.shape[0]:
+        if mat.shape[1] != row_or_column.shape[0]:
             raise TypeError(
-                f"matrix and new row do not have the same length. matrix: {mat.shape[1]}, row: {row.shape[1]}"
+                "Matrix and new row do not have the same shape along the second dimension."
             )
 
-        new_mat = sp.sparse.hstack([mat, rowOrCols])
+        new_mat = sp.sparse.hstack([mat, row_or_column])
 
     if new_mat is None:
         raise Exception("This should never happen")
diff --git a/src/mopsy/checkutils.py b/src/mopsy/checkutils.py
index f9763c8..0135438 100644
--- a/src/mopsy/checkutils.py
+++ b/src/mopsy/checkutils.py
@@ -8,13 +8,15 @@
 
 
 def check_axis(axis: Union[int, bool]):
-    """Check if axis has a correct value
+    """Check if axis has a correct value.
 
     Args:
-        axis (Union[int, bool]): axis, 0 for rows, 1 for columns
+        axis:
+            Axis, 0 for rows, 1 for columns
 
     Raises:
-        TypeError: if axis is neither 0 nor 1
+        ValueError:
+            If axis is neither 0 nor 1
     """
     if not (axis == 0 or axis == 1):
-        raise TypeError(f"axis is neither 0 or 1, provided {axis}")
+        raise ValueError(f"'axis' is neither 0 or 1, provided {axis}.")
diff --git a/src/mopsy/helpers.py b/src/mopsy/helpers.py
index 0d49661..57e2293 100644
--- a/src/mopsy/helpers.py
+++ b/src/mopsy/helpers.py
@@ -1,11 +1,12 @@
 from statistics import mean, median
-from .utils import get_matrix_type
-from .checkutils import check_axis
+from typing import Callable, Sequence, Union
 
-from typing import Sequence, Union, Callable, Any
 import numpy
 import scipy
 
+from .checkutils import check_axis
+from .utils import get_matrix_type
+
 __author__ = "jkanche"
 __copyright__ = "jkanche"
 __license__ = "MIT"
@@ -16,15 +17,23 @@ def colsum(
     group: Sequence = None,
     non_zero: bool = False,
 ) -> numpy.ndarray:
-    """Apply colsum
+    """Apply column sum.
 
     Args:
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        non_zero (bool): filter zero values ?
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of columns.
+            Defaults to None.
+
+        non_zero:
+            Whether to filter zero values.
+            Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix with the column sums.
     """
     return apply(sum, mat, group=group, axis=1, non_zero=non_zero)
 
@@ -34,15 +43,22 @@ def rowsum(
     group: Sequence = None,
     non_zero: bool = False,
 ) -> numpy.ndarray:
-    """Apply rowsum
+    """Apply row sum.
 
     Args:
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        non_zero (bool): filter zero values ?
+        mat:
+            Input matrix.
+
+        group:
+             Group vector, must be the same length as the number
+            of rows. Defaults to None.
+
+        non_zero:
+            Whether to filter zero values.
+            Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix with the row sums.
     """
     return apply(sum, mat, group=group, axis=0, non_zero=non_zero)
 
@@ -52,15 +68,22 @@ def colmean(
     group: Sequence = None,
     non_zero: bool = False,
 ) -> numpy.ndarray:
-    """Apply colmean
+    """Apply column mean.
 
     Args:
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        non_zero (bool): filter zero values ?
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of columns. Defaults to None.
+
+        non_zero:
+            Whether to filter zero values.
+            Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix with the column means.
     """
     return apply(mean, mat, group=group, axis=1, non_zero=non_zero)
 
@@ -70,15 +93,22 @@ def rowmean(
     group: Sequence = None,
     non_zero: bool = False,
 ) -> numpy.ndarray:
-    """Apply rowmean
+    """Apply row mean.
 
     Args:
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        non_zero (bool): filter zero values ?
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of rows. Defaults to None.
+
+        non_zero:
+            Whether to filter zero values.
+            Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix with the row means.
     """
     return apply(mean, mat, group=group, axis=0, non_zero=non_zero)
 
@@ -88,15 +118,22 @@ def colmedian(
     group: Sequence = None,
     non_zero: bool = False,
 ) -> numpy.ndarray:
-    """Apply colmedian
+    """Apply column median.
 
     Args:
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        non_zero (bool): filter zero values ?
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of columns. Defaults to None.
+
+        non_zero:
+            Whether to filter zero values.
+            Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix with the column medians.
     """
     return apply(median, mat, group=group, axis=1, non_zero=non_zero)
 
@@ -106,37 +143,55 @@ def rowmedian(
     group: Sequence = None,
     non_zero: bool = False,
 ) -> numpy.ndarray:
-    """Apply rowmedian
+    """Apply row median.
 
     Args:
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        non_zero (bool): filter zero values ?
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of rows. Defaults to None.
+
+        non_zero:
+            Whether to filter zero values.
+            Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix with the row medians.
     """
     return apply(median, mat, group=group, axis=0, non_zero=non_zero)
 
 
 def apply(
-    func: Callable[[list], Any],
+    func: Callable,
     mat: Union[numpy.ndarray, scipy.sparse.spmatrix],
     axis: Union[int, bool],
     group: Sequence = None,
     non_zero: bool = False,
 ):
-    """A generic apply function
+    """A generic `apply` function.
 
     Args:
-        func (Callable): function to be called.
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        axis (Union[int, bool]): 0 for rows, 1 for columns.
-        non_zero (bool): filter zero values ?
+        func:
+            Function to apply over the groups.
+
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of rows or columns depending on the axis.
+            Defaults to None.
+
+        axis:
+            0 for rows, 1 for columns.
+
+        non_zero:
+            Whether to filter zero values. Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A matrix containing the result of the function.
     """
     check_axis(axis)
 
@@ -145,25 +200,35 @@ def apply(
 
 
 def multi_apply(
-    funcs: Sequence[Callable[[list], Any]],
+    funcs: Sequence[Callable],
     mat: Union[numpy.ndarray, scipy.sparse.spmatrix],
     axis: Union[int, bool],
     group: Sequence = None,
     non_zero: bool = False,
 ):
-    """Apply multiple functions, the first axis
-        of the ndarray specifies the results of the inputs functions in
-        the same order
+    """A generic `multi_apply` to apply multiple function over the subset matrices.
 
     Args:
-        funcs (Sequence[Callable[[list], Any]]): functions to be called.
-        mat (Union[numpy.ndarray, scipy.sparse.spmatrix]): matrix
-        group (Sequence, optional): group variable. Defaults to None.
-        axis (Union[int, bool]): 0 for rows, 1 for columns.
-        non_zero (bool): filter zero values ?
+        func:
+            List of function to apply over the groups.
+
+        mat:
+            Input matrix.
+
+        group:
+            Group vector, must be the same length as the number
+            of rows or columns depending on the axis.
+            Defaults to None.
+
+        axis:
+            0 for rows, 1 for columns.
+
+        non_zero:
+            Whether to filter zero values. Defaults to False.
 
     Returns:
-        numpy.ndarray: matrix
+        A list of matrices, in the same order as the functions
+        containing the result of each the function.
     """
     check_axis(axis)
 
diff --git a/src/mopsy/mops.py b/src/mopsy/mops.py
index c88931c..474284e 100644
--- a/src/mopsy/mops.py
+++ b/src/mopsy/mops.py
@@ -1,6 +1,7 @@
 from itertools import groupby
+from typing import Any, Callable, Optional, Sequence, Tuple, Union
+
 import numpy as np
-from typing import Any, Callable, Tuple, Optional, Sequence, Union
 
 from .checkutils import check_axis
 
@@ -10,26 +11,33 @@
 
 
 class Mops:
-    """Base class for all matrix operations"""
+    """Base class for all matrix operations."""
 
     def __init__(self, mat, non_zero: bool = False) -> None:
-        """Intialize the matrix
+        """Intialize the matrix.
 
         Args:
-            mat (numpy.ndarray or scipy.sparse.spmatrix): a matrix
-            non_zero (bool): filter zero values ?
+            mat:
+                Input matrix.
+
+            non_zero:
+                Whether to filter zero values.
+                Defaults to False.
         """
         self.matrix = mat
         self.non_zero = non_zero
 
     def groupby_indices(self, group: Sequence) -> dict:
-        """From a group vector, get the list of indices that map to each group
+        """From a group vector, get the list of indices that map to each group.
 
         Args:
-            group (list): group variable, any list or array like object
+            group:
+                Group vector, expected to ne the same as the
+                number of rows or column.
 
         Returns:
-            dict: each group and the list of indices that map to it
+            A dictionary with each group name as the key and the values containing
+            the list of indices that map to it.
         """
         return {
             k: [x[0] for x in v]
@@ -39,15 +47,6 @@ def groupby_indices(self, group: Sequence) -> dict:
         }
 
     def _apply(self, func: Callable[[list], Any], axis: Union[int, bool]):
-        """Internal function that wraps numpy's apply_along_axis
-
-        Args:
-            func (Callable): a function to apply
-            axis (Union[int, bool]): 0 for rows, 1 for columns
-
-        Returns:
-            numpy.ndarray: a dense vector after appling group by
-        """
         if self.non_zero:
 
             def funcwrapper(mat):
@@ -64,19 +63,22 @@ def apply(
         group: Sequence = None,
         axis: Union[int, bool] = 0,
     ) -> Tuple[np.ndarray, Optional[Sequence]]:
-        """Apply a function to groups along an axis
+        """Apply a function to groups along an axis.
 
         Args:
-            func (Callable): a function to apply
-            group (list, optional): group variable. Defaults to None.
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
+            func:
+                List of function to apply over the groups.
+
+            group:
+                Group vector, must be the same length as the number
+                of rows or columns depending on the axis.
+                Defaults to None.
 
-        Raises:
-            Exception: ApplyFuncError, when a function cannot be applied
-            TypeError: if axis is neither 0 nor 1
+            axis:
+                0 for rows, 1 for columns.
 
         Returns:
-            Tuple[np.ndarray, Optional[Sequence]]: a tuple of matrix and its labels
+            A tuple of matrix and its labels.
         """
 
         check_axis(axis)
@@ -106,35 +108,33 @@ def multi_apply(
         group: list = None,
         axis: int = 0,
     ) -> Tuple[np.ndarray, Optional[Sequence]]:
-        """Apply multiple functions, the first axis
-        of the ndarray specifies the results of the inputs functions in
-        the same order
+        """Apply multiple functions, the first axis of the ndarray specifies the results of the inputs functions in the
+        same order.
 
         Args:
-            funcs (List[Callable[[list], Any]]): functions to be called.
-            group (list, optional): group variable. Defaults to None.
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
+            func:
+                List of function to apply over the groups.
+
+            group:
+                Group vector, must be the same length as the number
+                of rows or columns depending on the axis.
+                Defaults to None.
 
-        Raises:
-            Exception: ApplyFuncError, when a function cannot be applied
-            TypeError: if axis is neither 0 nor 1
+            axis:
+                0 for rows, 1 for columns.
 
         Returns:
-            Tuple[np.ndarray, Optional[Sequence]]: a tuple of matrix and its labels
+            A tuple of matrix and its labels.
         """
-        
+
         check_axis(axis)
 
         result = None
         rgroups = None
         try:
             if group is None:
-
                 tmats = [self._apply(f, axis=axis) for f in funcs]
-                nmats = [
-                    x[np.newaxis] if axis == 0 else x[np.newaxis].T
-                    for x in tmats
-                ]
+                nmats = [x[np.newaxis] if axis == 0 else x[np.newaxis].T for x in tmats]
                 result = nmats
             else:
                 rgroups = []
diff --git a/src/mopsy/nops.py b/src/mopsy/nops.py
index b72418a..b7a3d63 100644
--- a/src/mopsy/nops.py
+++ b/src/mopsy/nops.py
@@ -1,36 +1,34 @@
-from typing import Iterator, Tuple, Union, Sequence
-from .mops import Mops
+from typing import Iterator, Sequence, Tuple, Union
 
 import numpy as np
 
+from .mops import Mops
+
 __author__ = "jkanche"
 __copyright__ = "jkanche"
 __license__ = "MIT"
 
 
 class Nops(Mops):
-    """Internal representation for numpy arrays"""
+    """Internal representation for numpy arrays."""
 
     def __init__(self, mat: np.ndarray, non_zero: bool = False) -> None:
-        """Intialize with a numpy matrix
-
-        Args:
-            mat (numpy.ndarray): numpy matrix
-            non_zero (bool): filter zero values ?
-        """
         super().__init__(mat, non_zero=non_zero)
 
     def iter(
         self, group: Sequence[str] = None, axis: Union[int, bool] = 0
     ) -> Iterator[Tuple]:
-        """Iterator over groups and an axis
+        """Iterator over groups and an axis.
 
         Args:
-            group (Sequence[str], optional): group variable. Defaults to None.
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
+            group:
+                Group variable. Defaults to None.
+
+            axis:
+                0 for rows, 1 for columns. Defaults to 0.
 
         Yields:
-            Tuple (str, Nops): of group and the submatrix
+            A tuple (str, Nops) of group and the submatrix.
         """
         mat = self.matrix
 
@@ -42,7 +40,10 @@ def iter(
                 if axis == 0:
                     yield (
                         k,
-                        Nops(mat[v,], self.non_zero,),
+                        Nops(
+                            mat[v,],
+                            self.non_zero,
+                        ),
                     )
                 else:
                     yield (k, Nops(mat[:, v], self.non_zero))
diff --git a/src/mopsy/sops.py b/src/mopsy/sops.py
index 429a1b1..e5f84fc 100644
--- a/src/mopsy/sops.py
+++ b/src/mopsy/sops.py
@@ -1,11 +1,11 @@
-from .mops import Mops
-from .nops import Nops
+from statistics import mean
+from typing import Any, Callable, Iterator, Optional, Sequence, Tuple, Union
 
-from scipy import sparse as sp
 import numpy as np
-from statistics import mean
+from scipy import sparse as sp
 
-from typing import Callable, Any, Iterator, Tuple, Sequence, Optional, Union
+from .mops import Mops
+from .nops import Nops
 
 __author__ = "jkanche"
 __copyright__ = "jkanche"
@@ -13,26 +13,33 @@
 
 
 class Sops(Mops):
-    """Sops, Sparse Matrix Operation Class"""
+    """Sops, Sparse Matrix Operation Class."""
 
     def __init__(self, mat: sp.spmatrix, non_zero: bool = False) -> None:
         """Initialize the class from a scipy sparse matrix.
 
         Args:
-            mat (scipy.sparse.spmatrix): a scipy sparse matrix
-            non_zero (bool): filter zero values ?
+            mat:
+                Input scipy sparse matrix.
+
+            non_zero:
+                Whether to filter zero values.
+                Defaults to False.
         """
         super().__init__(mat, non_zero=non_zero)
 
     def iter(self, group: list = None, axis: Union[int, bool] = 0) -> Iterator[Tuple]:
-        """Iterator over groups and an axis
+        """Iterator over groups and an axis.
 
         Args:
-            group (list, optional): group variable. Defaults to None.
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
+            group:
+                Group variable. Defaults to None.
+
+            axis:
+                0 for rows, 1 for columns. Defaults to 0.
 
         Yields:
-            tuple (str, matrix): of group and the submatrix
+            a tuple (str, matrix) of group and the submatrix.
         """
         mat = self.matrix.tocsr() if axis == 0 else self.matrix.tocsc()
         if group is None:
@@ -43,21 +50,17 @@ def iter(self, group: list = None, axis: Union[int, bool] = 0) -> Iterator[Tuple
                 if axis == 0:
                     yield (
                         k,
-                        Sops(mat[v,], self.non_zero,),
+                        Sops(
+                            mat[v,],
+                            self.non_zero,
+                        ),
                     )
                 else:
                     yield (k, Sops(mat[:, v], self.non_zero))
 
-    def _apply(self, func: Callable[[list], Any], axis: Union[int, bool] = 0) -> np.ndarray:
-        """Apply a function over the matrix
-
-        Args:
-            func (Callable): function to apply over row or col wise vectors
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
-
-        Returns:
-            numpy.ndarray: a dense vector
-        """
+    def _apply(
+        self, func: Callable[[list], Any], axis: Union[int, bool] = 0
+    ) -> np.ndarray:
         mat = self.matrix.tocsc() if axis == 0 else self.matrix.tocsr()
         if self.non_zero:
             # reduction along an axis
@@ -96,18 +99,26 @@ def apply(
         group: Sequence = None,
         axis: Union[int, bool] = 0,
     ) -> Tuple[np.ndarray, Optional[Sequence]]:
-        """Apply a function to groups along an axis
+        """Apply a function to groups along an axis.
 
         Args:
-            func (Callable): a function to apply
-            group (list, optional): group variable. Defaults to None.
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
+            func:
+                List of function to apply over the groups.
+
+            group:
+                Group vector, must be the same length as the number
+                of rows or columns depending on the axis.
+                Defaults to None.
+
+            axis:
+                0 for rows, 1 for columns.
 
         Raises:
-            Exception: ApplyFuncError, when a function cannot be applied
+            Exception:
+                ApplyFuncError, when a function cannot be applied.
 
         Returns:
-            Tuple[np.ndarray, Optional[Sequence]]: a tuple of matrix and its labels
+            A tuple of matrix and its labels.
         """
         original_sparse_type = Sops.identify_sparse_type(self.matrix)
         mat, groups = super().apply(func, group, axis)
@@ -122,46 +133,51 @@ def multi_apply(
         group: list = None,
         axis: Union[int, bool] = 0,
     ) -> Tuple[np.ndarray, Optional[Sequence]]:
-        """Apply multiple functions, the first axis
-        of the ndarray specifies the results of the inputs functions in
-        the same order
+        """Apply multiple functions, the first axis of the ndarray specifies the results of the inputs functions in the
+        same order.
 
         Args:
-            funcs (List[Callable[[list], Any]]): functions to be called.
-            group (list, optional): group variable. Defaults to None.
-            axis (Union[int, bool], optional): 0 for rows, 1 for columns. Defaults to 0.
+            func:
+                List of function to apply over the groups.
+
+            group:
+                Group vector, must be the same length as the number
+                of rows or columns depending on the axis.
+                Defaults to None.
+
+            axis:
+                0 for rows, 1 for columns.
 
         Raises:
-            Exception: ApplyFuncError, when a function cannot be applied
+            Exception:
+                ApplyFuncError, when a function cannot be applied.
 
         Returns:
-            Tuple[np.ndarray, Optional[Sequence]]: a tuple of matrix and its labels
+            A tuple of matrix and its labels.
         """
         original_sparse_type = Sops.identify_sparse_type(self.matrix)
         mats, groups = super().multi_apply(funcs, group, axis)
-        cmats = [
-            Sops.convert_sparse_type(m, original_sparse_type) for m in mats
-        ]
+        cmats = [Sops.convert_sparse_type(m, original_sparse_type) for m in mats]
 
         return cmats, groups
 
     @staticmethod
     def identify_sparse_type(mat: sp.spmatrix):
-        """Identify the sparse matrix format
+        """Identify the sparse matrix format.
 
         Args:
-            mat (scipy.sparse.spmatrix): a scipy matrix
+            mat:
+                Input scipy matrix.
 
         Raises:
-            TypeError: matrix is not sparse
+            TypeError:
+                If matrix is not sparse.
 
         Returns:
-            an internal matrix representation object
+            An internal matrix representation object
         """
         if not isinstance(mat, sp.spmatrix):
-            raise TypeError(
-                f"mat is not a sparse representation, it is {type(mat)}"
-            )
+            raise TypeError(f"mat is not a sparse representation, it is {type(mat)}")
 
         if sp.isspmatrix_csc(mat):
             return "csc"
@@ -180,17 +196,21 @@ def identify_sparse_type(mat: sp.spmatrix):
 
     @staticmethod
     def convert_sparse_type(mat: sp.spmatrix, format: str):
-        """Convert to a sparse matrix format
+        """Convert to a sparse matrix format.
 
         Args:
-            mat (scipy.sparse.spmatrix): a numpy or scipy matrix
-            format (str): sparse matrix format, one of `identify_sparse_type()`
+            mat:
+                A numpy or scipy matrix.
+
+            format:
+                Sparse matrix format, one of `identify_sparse_type()`.
 
         Raises:
-            TypeError: matrix is not sparse
+            TypeError:
+                If matrix is not sparse.
 
         Returns:
-            an internal matrix representation object
+            An internal matrix representation object.
         """
         if isinstance(mat, np.ndarray):
             if format == "csc":
@@ -223,4 +243,4 @@ def convert_sparse_type(mat: sp.spmatrix, format: str):
             elif format == "lil":
                 return mat.tolil()
         else:
-            raise Exception(f"unknown matrix format")
+            raise Exception("unknown matrix format.")
diff --git a/src/mopsy/utils.py b/src/mopsy/utils.py
index df5ecc4..e800ab0 100644
--- a/src/mopsy/utils.py
+++ b/src/mopsy/utils.py
@@ -1,27 +1,32 @@
+from typing import Union
+
 import numpy as np
 import scipy.sparse as sp
+
 from .nops import Nops
 from .sops import Sops
 
-from typing import Union
-
 __author__ = "jkanche"
 __copyright__ = "jkanche"
 __license__ = "MIT"
 
 
 def get_matrix_type(mat: Union[np.ndarray, sp.spmatrix], non_zero: bool = False):
-    """Get an internal matrix state
+    """Get an internal matrix state.
 
     Args:
-        mat (Numpy.ndarray or scipy.sparse.spmatrix): a numpy or scipy matrix
-        non_zero (bool): filter zero values ?
+        mat:
+            An input numpy or scipy matrix.
+
+        non_zero:
+            Whether to filter zero value. Defaults to False.
 
     Raises:
-        Exception: TypeNotSupported, when the matrix type is not supported
+        Exception:
+            TypeNotSupported, when the matrix type is not supported.
 
     Returns:
-        an internal matrix representation object
+        An internal matrix representation object.
     """
     if isinstance(mat, np.ndarray):
         return Nops(mat, non_zero=non_zero)
diff --git a/tests/conftest.py b/tests/conftest.py
index 7c452b3..6b38a9e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,10 +1,9 @@
-"""
-    Dummy conftest.py for mopsy.
+"""Dummy conftest.py for mopsy.
 
-    If you don't know what this is for, just leave it empty.
-    Read more about conftest.py under:
-    - https://docs.pytest.org/en/stable/fixture.html
-    - https://docs.pytest.org/en/stable/writing_plugins.html
+If you don't know what this is for, just leave it empty.
+Read more about conftest.py under:
+- https://docs.pytest.org/en/stable/fixture.html
+- https://docs.pytest.org/en/stable/writing_plugins.html
 """
 
 # import pytest
diff --git a/tests/test_interface.py b/tests/test_interface.py
index a9cb45a..1108bc4 100644
--- a/tests/test_interface.py
+++ b/tests/test_interface.py
@@ -19,4 +19,3 @@ def test_apply_cols():
 def test_multiapply_cols():
     rmat = multi_apply([mean], mat, 1, None, False)
     assert rmat is not None
-
diff --git a/tests/test_sparse_add.py b/tests/test_sparse_add.py
index 0765299..56c9fb1 100644
--- a/tests/test_sparse_add.py
+++ b/tests/test_sparse_add.py
@@ -10,7 +10,7 @@
 def test_sparse_add_row():
     mat = eye(5).tocsr()
     tmat = sparse_append(mat, np.array([0, 0, 0, 0, 0]), axis=0)
-    
+
     assert tmat is not None
     assert tmat.shape[0] == mat.shape[0] + 1
     assert type(tmat) == type(mat)
@@ -23,4 +23,3 @@ def test_sparse_add_col():
     assert tmat is not None
     assert tmat.shape[1] == mat.shape[1] + 1
     assert type(tmat) == type(mat)
-