depman 0.3.2

depman
======

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A lightweight dependency manager for managing project dependencies in multiple contexts. The use case driving development is that of distinguishing between development, testing, and production dependencies in a simple and unified way. However, the application is general purpose and can be used in any project requiring the management of dependencies in multiple contexts.

Currently, only dependencies resolved via ``apt-get`` and ``pip`` are supported. However, support for other dependency types is planned for future releases (see `Future Features`_ for more details).

Installation
------------
::

$ pip install depman


Usage
-----
::

usage: depman [-h] [-f <depfile>] [-t <type>] [-o <outfile>] [--no-header]
<command> [<context>]

A lightweight dependency manager.

positional arguments:
<command> 'satisfy' satisfies the dependencies specified in
<depfile>. 'validate' only validates <depfile> and
does not perform any system operations. 'export'
exports requirements to a specified file (using -o)
<context> The dependency context to perform <command> on

optional arguments:
-h, --help show this help message and exit
-f <depfile>, --depfile <depfile>
The requirements file to load
-t <type>, --type <type>
Restrict operations to dependencies of this type
-o <outfile>, --outfile <outfile>
File to write results to
--no-header No export header

If not supplied, ``<depfile>`` and ``<context>`` default to ``requirements.yml`` and ``all``, respectively.

Example(s)
----------

Suppose you have the following ``requirements.yml`` in your current working directory::

includes:
dev:
- test

dev:
apt:
- libxml2-dev=2.9.1+dfsg1-5+deb8u2
- libxslt1-dev
pip:
- lxml
- Sphinx

test:
pip:
- nose
- coverage

prod:
pip:
- gevent:
version: <=1.0.2
- texttable
- six:
always_upgrade: yes
- syn>=0.0.10

This file specifies three dependency contexts: ``dev``, ``test``, ``prod``. In general, any top-level key in ``requirements.yml`` specifies a dependency context. The one exception to this rule is ``includes``, which defines inclusion relationships between contexts. In this example, the ``dev`` context includes the ``test`` context. As such, when ``depman satisfy test`` is run at the command line, ``depman`` will invoke ``pip`` to install ``nose`` and ``coverage``, if they do not exist on the system. On the other hand, when ``depman satisfy dev`` is run at the command line, ``depman`` will first invoke ``apt-get`` to install ``libxml1-dev`` (version ``2.9.1+dfsg1-5+deb8u2``) and ``libxslt1-dev`` and then invoke ``pip`` to install ``lxml``, ``Sphinx``, ``nose``, and ``coverage`` (in general, ``apt`` dependencies are processed before ``pip`` dependencies). Because ``test`` is "included" in ``dev``, its dependencies are processed whenever ``dev`` is processed.

``depman`` also accepts the special context ``all`` as a valid command line parameter. Running ``depman satisfy all`` causes ``depman`` to satisfy the dependencies in all of the defined dependency contexts. In this example, it would cause ``depman`` to satisfy the dependencies for ``dev``, ``test``, and ``prod``. Running ``depman satisfy`` is equivalent to running ``depman satisfy all``.

Currently, only two dependency types are supported in any context: ``apt`` and ``pip``. However, support for other dependency types is planned for future releases (see `Future Features`_ for more details).

Dependencies are specified in each context under each dependency type (i.e. ``apt`` or ``pip``) as YAML list elements. If the element is a string, the dependency in question will be treated as satisfied if some version of the package denoted by the string exists on the system. For more detailed dependency requirements, the name of the package can be listed as the key to a YAML dictionary of dependency options. This can be seen, for example, in the ``gevent`` dependency, in which a version less than of equal to ``1.0.2`` is specified as a requirement. Additionally, the ``six`` package contains the ``always_upgrade`` option, which causes ``depman`` to always attempt to upgrade the package, regardless of the current version installed.

Package version relations can be specified in various ways. In the ``prod`` context, ``pip`` is constrained to only install a version of ``syn`` that is greater than or equal to ``0.0.10``. Likewise, in the ``dev`` context, ``apt`` is constrained to install version ``2.9.1+dfsg1-5+deb8u2`` of ``libxml2-dev``. And, as seen above, the ``pip`` ``gevent`` dependency is constrained to a version less than or equal to ``1.0.2``

Export
~~~~~~

Dependencies can also be exported. In this example, running
::
depman export prod -t pip -o requirements.txt

will produce a file ``requirements.txt`` in the current directory that looks like::

# Auto-generated by depman 0.3.1
gevent<=1.0.2
six
syn>=0.0.10
texttable

The header comment can be suppressed by supplying the ``--no-header`` option.

.. _Future Features:

Future Features
---------------

The following features are planned for future releases:

* apt PPA support
* Relative order specification for dependency satisfaction
* Support for other package managers
* Support for scripted installs from source
* Export to requirements files for various package management systems