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Requirements
============
.. currentmodule:: packaging.requirements
Parse a given requirements line for specifying dependencies of a Python
project, using `PEP 508`_ which defines the scheme that has been implemented
by this module.
Usage
-----
.. doctest::
>>> from packaging.requirements import Requirement
>>> simple_req = Requirement("name")
>>> simple_req
<Requirement('name')>
>>> simple_req.name
'name'
>>> simple_req.url is None
True
>>> simple_req.extras
set()
>>> simple_req.specifier
<SpecifierSet('')>
>>> simple_req.marker is None
True
>>> # Requirements can be specified with extras, specifiers and markers
>>> req = Requirement('name[foo]>=2,<3; python_version>"2.0"')
>>> req.name
'name'
>>> req.extras
{'foo'}
>>> req.specifier
<SpecifierSet('<3,>=2')>
>>> req.marker
<Marker('python_version > "2.0"')>
>>> # Requirements can also be specified with a URL, but may not specify
>>> # a version.
>>> url_req.name
'name'
>>> url_req.url
>>> url_req.extras
set()
>>> url_req.marker
<Marker('os_name == "a"')>
Reference
---------
.. class:: Requirement(requirement)
This class abstracts handling the details of a requirement for a project.
Each requirement will be parsed according to PEP 508.
:param str requirement: The string representation of a requirement.
:raises InvalidRequirement: If the given ``requirement`` is not parseable,
then this exception will be raised.
.. attribute:: name
The name of the requirement.
.. attribute:: url
The URL, if any where to download the requirement from. Can be None.
.. attribute:: extras
A set of extras that the requirement specifies.
.. attribute:: specifier
A :class:`~.SpecifierSet` of the version specified by the requirement.
.. attribute:: marker
A :class:`~.Marker` of the marker for the requirement. Can be None.
.. exception:: InvalidRequirement
Raised when attempting to create a :class:`Requirement` with a string that
does not conform to PEP 508.