# Poetry: Dependency Management for Python

Poetry helps you declare, manage and install dependencies of Python projects,
ensuring you have the right stack everywhere.

![Poet Install](https://raw.githubusercontent.com/sdispater/poetry/master/assets/install.gif)

The package is **highly experimental** at the moment so expect things to change and break.
However, if you feel adventurous feedback and pull requests are greatly appreciated.

Also, be aware that the features described here are the goal that this library is aiming
for and, as of now, not all of them are implemented. The dependency management is pretty much
done while the packaging and publishin are not done yet.

And finally, Poetry's code is only compatible with Python 3.6+ but it can manage
Python project's with previous versions without any problem.

## Installation

```bash
pip install poetry
```

### Enable tab completion for Bash, Fish, or Zsh

`poetry` supports generating completion scripts for Bash, Fish, and Zsh.
See `poet help completions` for full details, but the gist is as simple as using one of the following:

```bash
# Bash
poetry completions bash > /etc/bash_completion.d/pyproject.bash-completion

# Bash (macOS/Homebrew)
poetry completions bash > $(brew --prefix)/etc/bash_completion.d/pyproject.bash-completion

# Fish
poetry completions fish > ~/.config/fish/completions/pyproject.fish

# Zsh
poetry completions zsh > ~/.zfunc/_poetry
```

*Note:* you may need to restart your shell in order for the changes to take 
effect.

For `zsh`, you must then add the following line in your `~/.zshrc` before
`compinit`:

```zsh
fpath+=~/.zfunc
```


## Introduction

`poetry` is a tool to handle dependencies installation, building and packaging of Python packages.
It only needs one file to do all of that: the new, [standardized](https://www.python.org/dev/peps/pep-0518/) `pyproject.toml`.

```toml
[tool.poetry]
name = "my-package"
version = "0.1.0"
description = "The description of the package"

license = "MIT"

authors = [
    "Sébastien Eustace <sebastien@eustace.io>"
]

readme = 'README.md'

repository = "https://github.com/sdispater/poetry"
homepage = "https://github.com/sdispater/poetry"

keywords = ['packaging', 'poetry']

[tool.pyproject.dependencies]
python = "~2.7 || ^3.2"  # Compatible python versions must be declared here
toml = "^0.9"
requests = "^2.13"
semantic_version = "^2.6"
pygments = "^2.2"
twine = "^1.8"
wheel = "^0.29"
pip-tools = "^1.8.2"
cleo = { git = "https://github.com/sdispater/cleo.git", branch = "master" }

[tool.pyproject.dev-dependencies]
pytest = "^3.0"
pytest-cov = "^2.4"
coverage = "<4.0"
httpretty = "^0.8.14"

[tool.pyproject.scripts]
poet = 'poet:app.run'
```

There are some things we can notice here:

* It will try to enforce [semantic versioning](<http://semver.org>) as the best practice in version naming.
* You can specify the readme, included and excluded files: no more `MANIFEST.in`.
`poetry` will also use VCS ignore files (like `.gitignore`) to populate the `exclude` section.
* Keywords (up to 5) can be specified and will act as tags on the packaging site.
* The dependencies sections support caret, tilde, wildcard, inequality and multiple requirements.
* You must specify the python versions for which your package is compatible.

`poetry` will also detect if you are inside a virtualenv and install the packages accordingly.
So, `poetry` can be installed globally and used everywhere.

`poetry` also comes with a full fledged dependency resolution library, inspired by [Molinillo](https://github.com/CocoaPods/Molinillo).

## Why?

Packaging system and dependency management in Python is rather convoluted and hard to understand for newcomers.
Even for seasoned developers it might be cumbersome at times to create all files needed in a Python project: `setup.py`,
`requirements.txt`, `setup.cfg`, `MANIFEST.in` and the newly added `Pipfile`.

So I wanted a tool that would limit everything to a single configuration file to do:
dependency management, packaging and publishing.

It takes inspiration in tools that exist in other languages, like `composer` (PHP) or `cargo` (Rust).

And, finally, there is no reliable tool to properly resolves dependencies in Python, so I started `poetry`
to bring an exhaustive depency resolver to the Python community.

### What about Pipenv?

In short: I do not like the CLI it provides, or some of the decisions made,
and I think we can do a better and more intuitive one. Here are a few things
that I don't like.

#### Dependency resolution

The dependency resolution is erratic and will fail even is there is a solution. Let's take an example:

```bash
pipenv install oslo.utils==1.4.0
```

will fail with this error:

```text
Could not find a version that matches pbr!=0.7,!=2.1.0,<1.0,>=0.6,>=2.0.0
```

while Poetry will get you the right set of packages:

```bash
poetry add oslo.utils=1.4.0
```

results in :

```text
  - Installing pytz (2018.3)
  - Installing netifaces (0.10.6)
  - Installing netaddr (0.7.19)
  - Installing oslo.i18n (2.1.0)
  - Installing iso8601 (0.1.12)
  - Installing six (1.11.0)
  - Installing babel (2.5.3)
  - Installing pbr (0.11.1)
  - Installing oslo.utils (1.4.0)
```

#### Pipfile.lock and environment markers

The Pipfile.lock file holds information about the environment in which
it has been generated. This is a bad design decision since in teams where
each member has a different environment, the diff will always include
this changes.

#### Install command

When you specify a package to the `install` command it will add it as a wildcard
dependency. This means that **any** version of this package can be installed which
can lead to compatibility issues.

Also, you have to explicitely tell it to not update the locked packages when you
installed new ones. This should be the default.

#### Remove command

The `remove` command will only remove the package specified but not its dependencies
if they are no longer needed.

You either have to use `sync` or `clean` to fix that.


Finally, the `Pipfile` is just a replacement from `requirements.txt` but in the end you will still need to 
populate your `setup.py` file (or `setup.cfg`) with the exact same dependencies you declared in your `Pipfile`.
So, in the end, you will still need to manage a few configuration files to properly setup your project.


## Commands


### new

This command will help you kickstart your new Python project by creating
a directory structure suitable for most projects.

```bash
poetry new my-package
```

will create a folder as follows:

```text
my-package
├── pyproject.toml
├── README.rst
├── my_package
    └── __init__.py
└── tests
    ├── __init__.py
    └── test_my_package
```

If you want to name your project differently than the folder, you can pass
the `--name` option:

```bash
poetry new my-folder --name my-package
```


### install

The `install` command reads the `pyproject.toml` file from the current directory, resolves the dependencies,
and installs them.

```bash
poetry install
```

If there is a `pyproject.lock` file in the current directory,
it will use the exact versions from there instead of resolving them.
This ensures that everyone using the library will get the same versions of the dependencies.

If there is no `pyproject.lock` file, Poetry will create one after dependency resolution.

You can specify to the command that you do not want the development dependencies installed by passing
the `--no-dev` option.

```bash
poetry install --no-dev
```

You can also specify the features you want installed
by passing the `--f|--features` option (See [Features](#features) for more info)

```bash
poetry install --features "mysql pgsql"
poetry install -f mysql -f pgsql
```

#### Options

* `--no-dev`: Do not install dev dependencies.
* `-f|--features`: Features to install (multiple values allowed).

### update

In order to get the latest versions of the dependencies and to update the `pyproject.lock` file,
you should use the `update` command.

```bash
poetry update
```

This will resolve all dependencies of the project and write the exact versions into `pyproject.lock`.

If you just want to update a few packages and not all, you can list them as such:

```bash
poetry update requests toml
```

#### Options

* `--dry-run` : Outputs the operations but will not execute anything (implicitly enables --verbose).

### add

The `add` command adds required packages to your `pyproject.toml` and installs them.

If you do not specify a version constraint,
poetry will choose a suitable one based on the available package versions.

```bash
poetry add requests pendulum
```

#### Options

* `--D|dev`: Add package as development dependency.
* `--optional` : Add as an optional dependency.
* `--dry-run` : Outputs the operations but will not execute anything (implicitly enables --verbose).


### remove

The `remove` command removes a package from the current
list of installed packages

```bash
poetry remove pendulum
```

#### Options

* `--D|dev`: Removes a package from the development dependencies.
* `--dry-run` : Outputs the operations but will not execute anything (implicitly enables --verbose).


### show

To list all of the available packages, you can use the `show` command.

```bash
poetry show
```

If you want to see the details of a certain package, you can pass the package name.

```bash
poetry show pendulum

name        : pendulum
version     : 1.4.2
description : Python datetimes made easy

dependencies:
 - python-dateutil >=2.6.1
 - tzlocal >=1.4
 - pytzdata >=2017.2.2
```

#### Options

* `--tree`: List the dependencies as a tree.
* `-l|--latest`: Show the latest version.
*  `-o|--outdated`: Show the latest version but only for packages that are outdated.


### package

The `package` command builds the source and wheels archives.

#### Options

* `--no-universal`: Do not build a universal wheel.
* `--no-wheels`: Build only the source package.
*  `-c|--clean`: Make a clean package.

### publish

This command builds (if not already built) and publishes the package to the remote repository.

It will automatically register the package before uploading if this is the first time it is submitted.

#### Options

* `-r|--repository`: The repository to register the package to (default: `pypi`). Should match a section of your `~/.pypirc` file.

### search

This command searches for packages on a remote index.

```bash
poetry search requests pendulum
```

#### Options

* `-N|--only-name`: Search only in name.

### lock

This command locks (without installing) the dependencies specified in `pyproject.toml`.

```bash
poetry lock
```


## The `pyproject.toml` file

A `pyproject.toml` file is composed of multiple sections.

### package

This section describes the specifics of the package

#### name

The name of the package. **Required**

#### version

The version of the package. **Required**

This should follow [semantic versioning](http://semver.org/). However it will not be enforced and you remain
free to follow another specification.

#### python-version

A list of Python versions for which the package is compatible. **Required**

#### description

A short description of the package. **Required**

#### license

The license of the package.

The recommended notation for the most common licenses is (alphabetical):

* Apache-2.0
* BSD-2-Clause
* BSD-3-Clause
* BSD-4-Clause
* GPL-2.0
* GPL-2.0+
* GPL-3.0
* GPL-3.0+
* LGPL-2.1
* LGPL-2.1+
* LGPL-3.0
* LGPL-3.0+
* MIT

Optional, but it is highly recommended to supply this.
More identifiers are listed at the [SPDX Open Source License Registry](https://www.spdx.org/licenses/).

#### authors

The authors of the package. This is a list of authors and should contain at least one author.

Authors must be in the form `name <email>`.

#### readme

The readme file of the package. **Required**

The file can be either `README.rst` or `README.md`.
If it's a markdown file you have to install the [pandoc](https://github.com/jgm/pandoc) utility so that it can be automatically
converted to a RestructuredText file.

You also need to have the [pypandoc](https://pypi.python.org/pypi/pypandoc/) package installed. If you install `poet` via
`pip` you can use the `markdown-readme` extra to do so.

```bash
pip install pypoet[markdown-readme]
```

#### homepage

An URL to the website of the project. **Optional**

#### repository

An URL to the repository of the project. **Optional**

#### documentation

An URL to the documentation of the project. **Optional**

#### keywords

A list of keywords (max: 5) that the package is related to. **Optional**

#### include and exclude

A list of patterns that will be included in the final package.

You can explicitly specify to Poet that a set of globs should be ignored or included for the purposes of packaging.
The globs specified in the exclude field identify a set of files that are not included when a package is built.

If a VCS is being used for a package, the exclude field will be seeded with the VCS’ ignore settings (`.gitignore` for git for example).

```toml
[package]
# ...
include = ["package/**/*.py", "package/**/.c"]
```

```toml
exclude = ["package/excluded.py"]
```

If you packages lies elsewhere (say in a `src` directory), you can tell `poet` to find them from there:

```toml
include = { from = 'src', include = '**/*' }
```

Similarly, you can tell that the `src` directory represent the `foo` package:

```toml
include = { from = 'src', include = '**/*', as = 'foo' }
```

### `dependencies` and `dev-dependencies`

Poet is configured to look for dependencies on [PyPi](https://pypi.org) by default.
Only the name and a version string are required in this case.

```toml
[dependencies]
requests = "^2.13.0"
```

If you want to use a private repository, you can add it to your `pyproject.toml` file, like so:

```toml
[[source]]
name = 'private'
url = 'http://example.com/simple'
```


#### Caret requirement

**Caret requirements** allow SemVer compatible updates to a specified version.
An update is allowed if the new version number does not modify the left-most non-zero digit in the major, minor, patch grouping.
In this case, if we ran `poet update requests`, poet would update us to version `2.14.0` if it was available,
but would not update us to `3.0.0`.
If instead we had specified the version string as `^0.1.13`, poet would update to `0.1.14` but not `0.2.0`.
`0.0.x` is not considered compatible with any other version.

Here are some more examples of caret requirements and the versions that would be allowed with them:

```text
^1.2.3 := >=1.2.3 <2.0.0
^1.2 := >=1.2.0 <2.0.0
^1 := >=1.0.0 <2.0.0
^0.2.3 := >=0.2.3 <0.3.0
^0.0.3 := >=0.0.3 <0.0.4
^0.0 := >=0.0.0 <0.1.0
^0 := >=0.0.0 <1.0.0
```

#### Tilde requirements

**Tilde requirements** specify a minimal version with some ability to update.
If you specify a major, minor, and patch version or only a major and minor version, only patch-level changes are allowed.
If you only specify a major version, then minor- and patch-level changes are allowed.

`~1.2.3` is an example of a tilde requirement.

```text
~1.2.3 := >=1.2.3 <1.3.0
~1.2 := >=1.2.0 <1.3.0
~1 := >=1.0.0 <2.0.0
```

#### Wildcard requirements

**Wildcard requirements** allow for any version where the wildcard is positioned.

`*`, `1.*` and `1.2.*` are examples of wildcard requirements.

```text
* := >=0.0.0
1.* := >=1.0.0 <2.0.0
1.2.* := >=1.2.0 <1.3.0
```

#### Inequality requirements

**Inequality requirements** allow manually specifying a version range or an exact version to depend on.

Here are some examples of inequality requirements:

```text
>= 1.2.0
> 1
< 2
!= 1.2.3
```

#### Multiple requirements

Multiple version requirements can also be separated with a comma, e.g. `>= 1.2, < 1.5`.

#### `git` dependencies

To depend on a library located in a `git` repository,
the minimum information you need to specify is the location of the repository with the git key:

```toml
[dependencies]
requests = { git = "https://github.com/requests/requests.git" }
```

Since we haven’t specified any other information,
Poetry assumes that we intend to use the latest commit on the `master` branch to build our project.
You can combine the `git` key with the `rev`, `tag`, or `branch` keys to specify something else.
Here's an example of specifying that you want to use the latest commit on a branch named `next`:

```toml
[dependencies]
requests = { git = "https://github.com/kennethreitz/requests.git", branch = "next" }
```

#### Python restricted dependencies

You can also specify that a dependency should be installed only for specific Python versions:

```toml
[dependencies]
pathlib2 = { version = "^2.2", python-versions = "~2.7" }
```

```toml
[dependencies]
pathlib2 = { version = "^2.2", python-versions = ["~2.7", "^3.2"] }
```

### `scripts`

This section describe the scripts or executable that will be installed when installing the package

```toml
[scripts]
poetry = 'poetry:console.run'
```

Here, we will have the `poetry` script installed which will execute `console.run` in the `poetry` package.

### `features`

Poetry supports features to allow expression of:

* optional dependencies, which enhance a package, but are not required; and
* clusters of optional dependencies.

```toml
[package]
name = "awesome"

[features]
mysql = ["mysqlclient"]
pgsql = ["psycopg2"]

[dependencies]
# These packages are mandatory and form the core of this package’s distribution.
mandatory = "^1.0"

# A list of all of the optional dependencies, some of which are included in the
# above `features`. They can be opted into by apps.
psycopg2 = { version = "^2.7", optional = true }
mysqlclient = { version = "^1.3", optional = true }
```

When installing packages, you can specify features by using the `-f|--features` option:

```bash
poet install --features "mysql pgsql"
poet install -f mysql -f pgsql
```

### `plugins`

Poetry supports arbitrary plugins wich work similarly to
[setuptools entry points](http://setuptools.readthedocs.io/en/latest/setuptools.html).
To match the example in the setuptools documentation, you would use the following:

```toml
[plugins] # Optional super table

[plugins."blogtool.parsers"]
".rst" = "some_module::SomeClass"
```

## Resources

* [Official Website](https://pyproject.eustace.io)
* [Issue Tracker](https://github.com/sdispater/poetry/issues)
