Jan 21, 2026

Chapter 9_Errors & Modules

Jan 21, 2026

1 min read

I. Errors

1. Overview

The try block lets you test a block of code for errors.

The except block lets you handle the error.

The else block lets you execute code when there is no error.

The finally block lets you execute code, regardless of the result of the try- and except blocks.

To throw (or raise) an exception if a condition occurs, use the raise keyword.

try:
  print(x)
except NameError: # Specific exceptions first
  print("Variable x is not defined")
except: # General exceptions last 
  print("Something else went wrong")
else:
  print("Nothing went wrong")
finally:
  print("The 'try except' is finished")

# the above order matters!


# Bare except: also catches `KeyboardInterrupt` and `SystemExit`, which is almost never what you want.
# Correct and safe: `except Exception:`

x = -1

if x < 0:
  raise Exception("Sorry, no numbers below zero") #  # discouraged: too generic

if x < 0:
    raise ValueError("x must be non-negative")

x = "hello"

if not type(x) is int: 
  raise TypeError("Only integers are allowed")

2. Custom Exception with a Message

class InvalidNameError(Exception):
    pass


# Usage:
name = "test1"
if name == "test1":
  raise InvalidNameError(f"Invalid name: {name}")


# Output:
"""
Traceback (most recent call last):
  File "c:\Users\...\codeTest.py", line 9, in <module>
    raise InvalidNameError(f"Invalid name: {name}")
InvalidNameError: Invalid name: test1

"""

II. Modules & Packages

1. Terminology

A script is a Python file (.py) that is intended to be executed directly, usually to perform some task.

A module is a Python file that is intended to be imported by other Python code, rather than run directly.

package: A directory full of python code to be imported.

e.g. numpy

subpackage: A smaller package inside a package.

e.g. numpy.random

library: Either a package, or a collection of packages.

2. Creating your first python package

my_package/       
├── __init__.py
└── module.py

module.py contains all the package code.

__init__.py marks this directory as a python package. ( used to structure the package imports later )

3. Subpackages

mysklearn/                  ← package
├── __init__.py
│
├── preprocessing/          ← subpackage
│   ├── __init__.py
│   ├── normalize.py        ← module
│   └── standardize.py      ← module
│
├── regression/             ← subpackage
│   ├── __init__.py
│   └── regression.py       ← module
│
└── utils.py                ← module

you should place closely related function and classes in the same module, and related modules in the same subpackage.

4. package, subpackage and module documentation

Package doc is placed as a docstring at the top of __init__.py and summarizes the whole package.
Subpackage doc is similarly placed at the top of the subpackage’s __init__.py and describes what kind of modules it groups.
Module doc is written at the top of the module file and describes what that file provides.

mysklearn/__init__.py

"""
mysklearn

A lightweight educational machine learning package.
Provides basic preprocessing and regression utilities
implemented from scratch, for learning purposes.
"""

This documents the whole package.

mysklearn/preprocessing/__init__.py

"""
Preprocessing subpackage.

Contains data preprocessing utilities such as
normalization and standardization functions.
"""
> Each subpackage explains what kind of modules it groups.


---
<br>

`mysklearn/preprocessing/normalize.py`
```python
"""
Normalization utilities.

Functions for scaling numerical data to a fixed range,
typically [0, 1].
"""

Documents what this specific file provides.

5. Structuring imports

Note! A module containing relative imports cannot be executed directly with python file.py. (only works inside packages)

5.1 Without package imports

When you do:

import package

Only the package is imported.
Subpackages and modules are NOT imported automatically.

You must import them explicitly:

import package.subpackage
import package.subpackage.module

Note: import package.subpackage does not import the subpackage’s modules.

The solution is internal imports: ( import modules into subpackages and subpackages into the package)

5.2 importing subpackages into `packages`

mysklearn/                  
├── __init__.py   ← Here!
│
├── preprocessing/          
│   ├── __init__.py
│   ├── normalize.py        
│   └── standardize.py      
│
├── regression/             
│   ├── __init__.py
│   └── regression.py       
│
└── utils.py

In mysklearn/__init__.py

Using absolute imports

from mysklearn import preprocessing

Used most - more explicit

Using relative imports

from . import preprocessing

Used sometimes - shorter and sometimes simpler

. means the current file’s parent directory

After this, the subpackage itself is accessible, but its modules are not imported automatically.

5.3 importing modules into `subpackages/packages`

mysklearn/                  
├── __init__.py  
│
├── preprocessing/          
│   ├── __init__.py   ← Here!
│   ├── normalize.py        
│   └── standardize.py      
│
├── regression/             
│   ├── __init__.py
│   └── regression.py       
│
└── utils.py

In mysklearn/preprocessing/__init__.py

Using absolute imports

from mysklearn.preprocessing import normalize

Using relative imports

from . import normalize

5.4 importing functions into `subpackage`

Assuming you want only one function to be accessible to users, the others are only helper functions

mysklearn/                  
├── __init__.py  
│
├── preprocessing/          
│   ├── __init__.py   ← Here!
│   ├── normalize.py        
│   └── standardize.py      
│
├── regression/             
│   ├── __init__.py
│   └── regression.py       
│
└── utils.py

In mysklearn/preprocessing/__init__.py

Using absolute imports

from mysklearn.preprocessing.normalize import normalize_data_func

Using relative imports

from .normalize import normalize_data_func

With this, you can use the following shorter import path to access it:mysklearn.preprocessing.normalize_data_func

5.5 importing between sibling modules

sometimes if a module file is getting too big, you might split it into multiple files.

here some of the functions from normalize have been moved to funcs.py

but we still need to use them inside the normalize module

mysklearn/                  
├── __init__.py  
│
├── preprocessing/          
│   ├── __init__.py   
│   ├── normalize.py  ← Here!
|   ├── funcs.py
│   └── standardize.py      
│
├── regression/             
│   ├── __init__.py
│   └── regression.py       
│
└── utils.py

In normalize.py

Using absolute imports

from mysklearn.preprocessing.funcs import (mymax, mymin)

Using relative imports

from .funcs import mymax, mymin

5.6 import between modules far apart

mysklearn/                  
├── __init__.py  
│
├── preprocessing/          
│   ├── __init__.py   
│   ├── normalize.py  ← Here!
|   ├── funcs.py
│   └── standardize.py ← Here!     
│
├── regression/             
│   ├── __init__.py
│   └── regression.py ← Here!    
│
└── utils.py

A custom exception MyException is in utils.py

In normalize.py, standardize.py and regression.py

Using absolute imports

from mysklearn.utils import MyException

Using relative imports

from ..utils import MyException

5.7 Relative import cheat sheet

from . import module
- From current directory, import module
from .. import module
- From one directory up, import module
from .module import function
- From module in current directory, import function
from ..subpackage.module import function
- From subpackage one directory up, from module in that subpackage, import function

6. Install Your Package

6.1 Why install your package?

home/
├── mysklearn                  <-- in same directory
│   ├── __init__.py
│   ├── preprocessing
│   │   ├── __init__.py
│   │   ├── normalize.py
│   │   └── standardize.py
│   ├── regression
│   │   ├── __init__.py
│   │   └── regression.py
│   └── utils.py
└── example_script.py          <-- in same directory

inside example_script.py

import mysklearn
# This Import works because the script and the package are in the same directory.

If the script and the package are in different directories, Python will not find the package by default.

This results in an import error.

home/
|-- mypackages
|   |-- mysklearn     <---
|   |   |-- __init__.py
|   |   |-- preprocessing
|   |   |   |-- __init__.py
|   |   |   |-- normalize.py
|   |   |   `-- standardize.py
|   |   `-- regression
|   |       |-- __init__.py
|   |       `-- regression.py
`-- myscripts
    `-- example_script.py     <---

Solution: Install the package so Python finds it from any location.

6.2 How to make your package installable?

Setup.py

Is used to install the package.
Contains metadata on the package.

setup.py is still supported but considered legacy. Modern projects use pyproject.toml

Step1: Restructure your package directory

mysklearn/           <-- outer directory
|-- mysklearn        <--- inner source code directory
|   |-- __init__.py
|   |-- preprocessing
|   |   |-- __init__.py
|   |   |-- normalize.py
|   |   |-- standardize.py
|   |-- regression
|   |   |-- __init__.py
|   |   |-- regression.py
|   |-- utils.py
|-- setup.py         <-- setup script in outer

Place the package source and setup.py inside one outer folder named like the package.

This naming choice follows common Python project structure conventions.

Step2: Create setup.py file

# Import required functions
from setuptools import setup, find_packages

# Call setup function
setup(
    author="James Fulton",
    description="A complete package for linear regression.",
    name="mysklearn",
    version="0.1.0",
    packages=find_packages(include=["mysklearn", "mysklearn.*"]),
)

version number = (major number) . (minor number) . (patch number)

Editable installation

pip install -e .

pip runs setup.py for you

. = package in current dir

-e= editable :installs in editable mode so changes apply without reinstalling the package.

7. Dealing with dependencies

Other packages you import inside your package.

7.1 Adding dependencies to `setup.py`

from setuptools import setup, find_packages

setup(
  ...
  install_requires=["pandas", "scipy", "matplotlib"]
)

7.2 Controlling dependency version

from setuptools import setup, find_packages

setup(
  ...
  install_requires=[
    "pandas>=1.0",         # good
    "scipy==1.1",          # bad
    "matplotlib>=2.2.1,<3" # good
  ]
)

# Allow as many package versions as possible
# Get rid of unused dependencies

7.3 Python versions

from setuptools import setup, find_packages

setup(
  ...
  python_requires=">=3.8, !=3.0.*, !=3.1.*",
)
# `*` must be used when we are excluding version numbers.

7.4 Making an env for developers

show all the package versions used using: pip freeze

7.4.1 Save package requirements to a file

pip freeze > requirements.txt

7.4.2 install requirements from file

pip install -r requirements.txt

mysklearn/
|-- mysklearn
|   |-- __init__.py
|   |-- preprocessing
|   |   |-- __init__.py
|   |   |-- normalize.py
|   |   |-- standardize.py
|   |-- regression
|   |   |-- __init__.py
|   |   |-- regression.py
|   |-- utils.py
|-- setup.py
|-- requirements.txt   <-- developer environment

install_requires → users

requirements.txt → developers

8. Including licences and writing READMEs

mysklearn/
|-- mysklearn
|   |-- __init__.py
|   |-- preprocessing
|   |   |-- ...
|   |-- regression
|   |   |-- ...
|   |-- utils.py
|-- setup.py
|-- requirements.txt
|-- LICENSE        <--- new files
|-- README.md      <--- added to top directory
|-- MANIFEST.in     <--- ensures non-code files are packaged

MANIFEST.in This file tells the packaging tools specifically which extra files to include.

because by default readme and license are not included when someone installs your package.

MANIFEST.in content:

include LICENSE
include README.md

9. Publishing your package

PyPI (Python package Index) (Online code repo)

pip installs packages from here.

Anyone can upload packages. (free)

When you upload to PyPI you upload a package distribution

Distribution package - a bundled version of your package which is ready to install.

Source distribution - a distribution package which is mostly your source code.

wheel distribution - a distribution package which has been processed to make it faster to install. (preferred)

when you upload to PyPI, it’s good practice to upload both wheel and source distribution.

9.1 How to build `wheel` and `source` distributions`

python setup.py sdist bdist_wheel

sdist = source distribution

bdist_wheel = wheel distribution

Results:

mysklearn/
|-- mysklearn
|-- setup.py
|-- requirements.txt
|-- LICENSE
|-- README.md
|-- dist               <--- a dir that contains the distribution files
|   |-- mysklearn-0.1.0-py3-none-any.whl
|   |-- mysklearn-0.1.0.tar.gz
|-- build <--- temporary directory used during the compilation and packaging process
|-- mysklearn.egg-info <-- contains metadata about the package for package managers like pip.

9.2 Upload your distributions

To PyPI

twine upload dist/*

To TestPyPI

twine upload -r testpypi dist/*

9.3 How other people can install your package

Install package from PyPI

pip install mysklearn

Install package from TestPyPI

pip install --index-url https://test.pypi.org/simple
            --extra-index-url https://pypi.org/simple
            mysklearn

10. Testing your package

Good packages brag about how many tests they have.

10.1 Writing tests

def get_ends(x):
    """Get the first and last element in a list"""
    return x[0], x[-1]

def test_get_ends():
    assert get_ends([1,5,39,0]) == (1,0)
    assert get_ends(['n','e','r','d']) == ('n','d') # If something goes wrong -> the test function raise an AssertionError

10.2 Organizing tests inside your package

Directory Structure:

mysklearn/
|-- mysklearn     <-- package
|-- tests         <-- tests directory
|-- setup.py
|-- LICENSE
|-- MANIFEST.in

Test directory layout

mysklearn/tests/
|-- __init__.py  <-- empty: Modern `pytest` does not need it.
|-- preprocessing
|   |-- __init__.py
|   |-- test_normalize.py
|   |-- test_standardize.py
|-- regression
|   |-- __init__.py
|   |-- test_regression.py
|-- test_utils.py

Code directory layout

mysklearn/mysklearn/
|-- __init__.py
|-- preprocessing
|   |-- __init__.py
|   |-- normalize.py
|   |-- standardize.py
|-- regression
|   |-- __init__.py
|   |-- regression.py
|-- utils.py

Inside the test module, there should be a test function for each function defined in the source module

Example:

Inside test_normalize.py

from mysklearn.preprocessing.normalize import (
    find_max, find_min, normalize_data
)

def test_find_max():
    assert find_max([1,4,7,1])==7

def test_find_min():
    assert ...

def test_normalize_data():
    assert ...

Inside normalize.py

def find_max(x):
    ...
    return x_max

def find_min(x):
    ...
    return x_min

def normalize_data(x):
    ...
    return x_norm

10.3 Running test with `pytest`

mysklearn/ <-- navigate to here
|-- mysklearn
|-- tests
|-- setup.py
|-- LICENSE
|-- MANIFEST.in

pytest

pytest looks inside the test directory.

it looks for modules like test_modulename.py

it looks for functions like test_functionname()

it runs these functions and shows output.

Output

Example1

============================= test session starts ==============================
platform linux -- Python 3.7.9, pytest-6.1.2, py-1.9.0, pluggy-0.13.1
rootdir: /home/workspace/mypackages/mysklearn    <--   ran in this directory
collected 6 items                                <--   found 6 test functions

tests/preprocessing/test_normalize.py ...                              [ 50%]  <-- progress indicator
tests/preprocessing/test_standardize.py ...                            [100%]

============================== 6 passed in 0.23s ===============================

Example2

============================= test session starts ==============================
...
tests/preprocessing/test_normalize.py .F.                              [ 50%]
tests/preprocessing/test_standardize.py ...                            [100%]

==================================== FAILURES ==================================
_________________________________ test_mymax _________________________________
...

tests/preprocessing/test_normalize.py:10: AssertionError
=========================== short test summary info ============================
FAILED tests/preprocessing/test_normalize.py::test_mymax - assert -100 == 100    <-- test_mymax
========================= 1 failed, 5 passed in 0.17s ==========================

10.4 Testing your package with different environments

To manually test your package with multiple Python versions, you must:

Install all required Python versions.
Create an environment for each Python version.
Install your package and all its dependencies in each environment.
Run pytest in each environment.

A better solution is tox, a tool designed to automate testing with multiple Python versions: But you still need to:

Install all required Python versions.
run tox.

tox uses Python versions already installed on the system; it does not download them.

tox automatically creates isolated environments for each version.

It installs the package and dependencies in each environment.

It runs the test suite automatically.

10.4.1 Step1: Configure `tox`

Configuration file - tox.ini

mysklearn/
|-- mysklearn
|   |-- ...
|-- tests
|   |-- ...
|-- setup.py
|-- LICENSE
|-- MANIFEST.in
|-- tox.ini   <--- configuration file

In tox.ini

[tox]  <-- Headings.
envlist = py38, py39, py310, py311  <-- to test version `X.Y` add pyXY to `envlist`.

[testenv] <-- specify what will happen after package and dependencies installation.
deps = pytest <-- because pytest isn't installed by package dependencies we need to specify it as a tox dependency.
commands =  <-- must be shell commands.
  pytest
  echo "run more commands"
  ...

10.4.2 Step2: Running `tox`

mysklearn/    <-- navigate to here
|-- mysklearn
|   |-- ...
|-- tests
|   |-- ...
|-- setup.py
|-- LICENSE
|-- MANIFEST.in
|-- tox.ini

tox

Success Example Output

user@machine:~/mysklearn$ tox
.pkg: setup: /home/user/mysklearn/setup.py
.pkg: build_wheel: mysklearn-0.1.0-py3-none-any.whl

py38: install_deps: pytest
py38: install_package: mysklearn-0.1.0-py3-none-any.whl
py38: commands[0]> python --version
Python 3.8.10
py38: commands[1]> pytest
============================= test session starts ==============================
platform linux -- Python 3.8.10, pytest-7.1.2, pluggy-1.0.0
collected 12 items
tests/preprocessing/test_normalize.py .....
tests/preprocessing/test_standardize.py .....
tests/regression/test_regression.py ..
============================== 12 passed in 0.46s ==============================

py39: install_deps: pytest
py39: install_package: mysklearn-0.1.0-py3-none-any.whl
py39: commands[0]> python --version
Python 3.9.18
py39: commands[1]> pytest
============================== 12 passed in 0.43s ==============================

py310: install_deps: pytest
py310: install_package: mysklearn-0.1.0-py3-none-any.whl
py310: commands[0]> python --version
Python 3.10.13
py310: commands[1]> pytest
============================== 12 passed in 0.41s ==============================

py311: install_deps: pytest
py311: install_package: mysklearn-0.1.0-py3-none-any.whl
py311: commands[0]> python --version
Python 3.11.7
py311: commands[1]> pytest
============================== 12 passed in 0.39s ==============================

___________________________________ summary ____________________________________
  py38: commands succeeded
  py39: commands succeeded
  py310: commands succeeded
  py311: commands succeeded
  congratulations :)

Error case example

...
___________________________________ summary ____________________________________
  py38: commands succeeded
  py39: commands succeeded
ERROR:   py310: commands failed
  py311: commands succeeded

tox will skip Python versions not installed on the system.

11. Keeping your package stylish

11.1 Overview

Standard Python style is described in PEP8

a style guide dictates how code should be laid out.

flake8 static code checker - reads code but doesn’t run.

flake8 features.py

features.py:2:1: F401 'math' imported but unused
..

<filename>:<line number>:<character number>:<error code> <description>

Example

2:1: F401 'math' imported but unused
4:1: E302 expected 2 blank lines, found 1
7:1: E302 expected 2 blank lines, found 0
5:4: E111 indentation is not a multiple of four
6:4: E111 indentation is not a multiple of four
9:5: F841 local variable 'mean_x' is assigned to but never used
..

11.2 Breaking the rules on purpose

# noqa (no quality assurance)
x = 6 * x**2 + 2 * x + 4 # noqa
y = 7 + x**5 + 4 * x # noqa: E222  <-- for a specific error.

11.3 Ignoring style violation without comment

flake8 --ignore E222 quadratic.py

flake8 --select F401, F841 features.py

11.4 Choosing package settings using setup.cfg

Creating a setup.cfg to store settings

[flake8]

ignore = E302
exclude = setup.py

per-file-ignores =
    example_package/example_package.py: E222

.
|-- example_package
|   |-- __init__.py
|   `-- example_package.py
|-- tests
|   |-- __init__.py
|   `-- test_example_package.py
|-- README.rst
|-- LICENSE
|-- MANIFEST.in
|-- setup.py
`-- setup.cfg

Run flake8 on the whole package at once

You have to navigate to the top of the package, and run flake8 from the terminal.

12. Rapid Package Development

12.1 Faster package development with templates

cookiecutter

Can be used to create empty Python packages.

cookiecutter <template-url>

More templates Here

cookiecutter https://github.com/audreyr/cookiecutter-pypackageMore

full_name [Audrey Roy Greenfeld]: James Fulton
email [audreyr@example.com]: james@email.com
github_username [audreyr]: MyUsername
project_name [Python Boilerplate]: mysklearn
project_slug [mysklearn]: mysklearn

Project slug - the name used in pip install name

...
project_short_description [Python Boilerplate ...]: A Python package for linear
    regression.
pypi_username [MyUsername]:
version [0.1.0]:

description can be manually modified in the readme file later

...
use_pytest [n]: y <-- to use `pytest`
use_pypi_deployment_with_travis [y]: n
add_pyup_badge [n]: n

...
Select command_line_interface:
1 - Click
2 - Argparse
3 - No command-line interface
Choose from 1, 2, 3 [1]: 3
create_author_file [y]: y

...
Select open_source_license:
1 - MIT license
2 - BSD license
3 - ISC license
4 - Apache Software License 2.0
5 - GNU General Public License v3
6 - Not open source
Choose from 1, 2, 3, 4, 5, 6 [1]: 6

Final result

mysklearn/
|-- mysklearn/
|   |-- __init__.py
|   `-- mysklearn.py
|-- tests/
|   |-- __init__.py
|   `-- test_mysklearn.py
|-- MANIFEST.in
|-- README.rst
|-- requirements_dev.txt
|-- setup.cfg
|-- setup.py
|-- tox.ini
|-- AUTHORS.rst
|-- CONTRIBUTING.rst
|-- HISTORY.rst
`-- Makefile
...  <--- This part can be simply deleted.
...
|-- docs/ 
|-- .github/
|-- .editorconfig
|-- .gitignore
`-- .travis.yml

12.2 Version numbers and history

12.2.1 Overview

CONTRIBUTING.md

Invites other developers to work on your package.

Tell them how to get started.

HISTORY.md

known as history, release notes or changelog.

Tell users what has changed between versions.

Contains:

Section for each released version
Bullet points of the important changes
Subsections for:
- Improvements to existing functions
- New additions
- Bugs that have been fixed
- Deprecations

Example:

# History

## 0.3.0
### Changed
- Regression fitting sped up using NumPy operations.
### Deprecated
- Support for Python 3.5 has ended.
- `regression.regression` module has been removed.

## 0.2.1
### Fixed
- Fixed bug causing intercepts of zero.

## 0.2.0
### Added
- Multiple linear regression now available in new `regression.multiple_regression` module.
### Deprecated
- 0.2.x will be the last version that supports Python 3.5.
- `regression.regression` module has been renamed `regression.single_regression`. `regression.regression` will be removed in next minor release.

Note:

Increase version number when ready for new release.

Cannot upload to PyPI if not changed.

12.2.2 How to update the version number

mysklearn/
|-- mysklearn/
|   |-- __init__.py          <--- TOP level __init__.py
|   `-- mysklearn.py
|-- setup.py                 <--- 
...

In setup.py

# Import required functions
from setuptools import setup, find_packages

# Call setup function
setup(
    ...
    version='0.1.0',  # <--
    ...
)

In Top level __init__.py

"""
Linear regression for Python
============================

mysklearn is a complete package for implementing
linear regression in python.
"""

__version__ = '0.1.0'  # <---

this allows:

print(mysklearn.__version__) # 0.1.0

12.2.3 `bumpversion` Convenient tool to update all package version numbers

mysklearn/           <-- navigate to here
|-- mysklearn/
|   |-- __init__.py
|   `-- mysklearn.py
|-- setup.py
...

bumpversion major

bumpversion minor

bumpversion patch

12.3 Makefiles and classifiers

Makefiles which will speed up your development

Classifiers which will help people find your package.

12.3.1 Classifiers

Classifiers provide metadata for your package to help users find it on the Python Package Index (PyPI).

Key Metadata to Include:

Package status (e.g., Alpha, Beta, Production)
Your intended audience (e.g., Developers, Science/Research)
License type (e.g., MIT, Apache)
Language (e.g., English)
Versions of Python supported (e.g., 3.6, 3.7, 3.8)

Example inside setup.py:

...
setup(
    ...
    classifiers=[
        'Development Status :: 2 - Pre-Alpha',
        'Intended Audience :: Developers',
        'License :: OSI Approved :: MIT License',
        'Natural Language :: English',
        'Programming Language :: Python :: 3',
        'Programming Language :: Python :: 3.6',
        'Programming Language :: Python :: 3.7',
        'Programming Language :: Python :: 3.8',
    ],
    ...
)

12.3.2 Makefiles

Used to automate parts of building your package.

simplifies common development tasks into short commands (functions).

clean-build: ## Remove build artifacts
	rm -fr build/
	rm -fr dist/
	rm -fr .eggs/

dist: clean-build ## Build source and wheel package
	python3 setup.py sdist bdist_wheel

test: ## run tests quickly with the default Python
  pytest

release: ## package and upload a release
  twine upload dist/*

General Syntax

function/cmd_Name: prerequisites ## Description of the function
  the cmd/list of cmds

Usage

mysklearn/ <--- navigate to here
...
|-- README.md
|-- setup.py
|-- Makefile
...

In CLI

make <function-name>

Makefile summary

make help

Output:

clean           remove all build, test, coverage and Python artifacts
clean-build     remove build artifacts
clean-pyc       remove Python file artifacts
clean-test      remove test and coverage artifacts
lint            check style with flake8
test            run tests quickly with the default Python
test-all        run tests on every Python version with tox
release         package and upload a release
dist            builds source and wheel package
install         install the package to the active Python's site-packages

13. `name == "main"`

__name__ is a special variable in Python:

If the file is run directly, __name__ is "__main__".
If the file is imported, __name__ is the module’s name.

Code inside if __name__ == "__main__": runs only when executed directly.

def greet():
    print("Hello!")

if __name__ == "__main__":
    greet()  # runs only when file executed directly

Chapter 9_Errors & Modules

I. Errors

1. Overview

2. Custom Exception with a Message

II. Modules & Packages

1. Terminology

2. Creating your first python package

3. Subpackages

4. package, subpackage and module documentation

5. Structuring imports

5.1 Without package imports

5.2 importing subpackages into packages

5.3 importing modules into subpackages/packages

5.4 importing functions into subpackage

5.5 importing between sibling modules

5.6 import between modules far apart

5.7 Relative import cheat sheet

6. Install Your Package

6.1 Why install your package?

6.2 How to make your package installable?

7. Dealing with dependencies

7.1 Adding dependencies to setup.py

7.2 Controlling dependency version

7.3 Python versions

7.4 Making an env for developers

7.4.1 Save package requirements to a file

7.4.2 install requirements from file

8. Including licences and writing READMEs

9. Publishing your package

9.1 How to build wheel and source distributions`

9.2 Upload your distributions

9.3 How other people can install your package

10. Testing your package

10.1 Writing tests

10.2 Organizing tests inside your package

10.3 Running test with pytest

10.4 Testing your package with different environments

10.4.1 Step1: Configure tox

10.4.2 Step2: Running tox

11. Keeping your package stylish

11.1 Overview

11.2 Breaking the rules on purpose

11.3 Ignoring style violation without comment

11.4 Choosing package settings using setup.cfg

12. Rapid Package Development

12.1 Faster package development with templates

12.2 Version numbers and history

12.2.1 Overview

12.2.2 How to update the version number

12.2.3 bumpversion Convenient tool to update all package version numbers

12.3 Makefiles and classifiers

12.3.1 Classifiers

12.3.2 Makefiles

13. __name__ == "__main__"

5.2 importing subpackages into `packages`

5.3 importing modules into `subpackages/packages`

5.4 importing functions into `subpackage`

7.1 Adding dependencies to `setup.py`

9.1 How to build `wheel` and `source` distributions`

10.3 Running test with `pytest`

10.4.1 Step1: Configure `tox`

10.4.2 Step2: Running `tox`

12.2.3 `bumpversion` Convenient tool to update all package version numbers

13. `name == "main"`