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# Requirement Specifiers

pip supports installing from a package index using a requirement specifier. Generally speaking, a requirement specifier is composed of a project name followed by optional version specifiers.

PEP 508 contains a full specification of the format of a requirement.

Added in version 6.0: Support for environment markers.

Added in version 19.1: Support for the direct URL reference form.

## Overview

A requirement specifier comes in two forms:

- name-based, which is composed of:

  - a package name (eg: `requests`)

  - optionally, a set of “extras” that serve to install optional dependencies (eg: `security`)

  - optionally, constraints to apply on the version of the package

  - optionally, environment markers

- URL-based, which is composed of:

  - a package name (eg: `requests`)

  - optionally, a set of “extras” that serve to install optional dependencies (eg: `security`)

  - a URL for the package

  - optionally, environment markers

## Examples

A few example name-based requirement specifiers:

    SomeProject
    SomeProject == 1.3
    SomeProject >= 1.2, < 2.0
    SomeProject[foo, bar]
    SomeProject ~= 1.4.2
    SomeProject == 5.4 ; python_version < '3.8'
    SomeProject ; sys_platform == 'win32'
    requests [security] >= 2.8.1, == 2.8.* ; python_version < "2.7"

Note

Use quotes around specifiers in the shell when using `>`, `<`, or when using environment markers.

Do not use quotes in requirement files. There is only one exception: pip v7.0 and v7.0.1 (from May 2015) required quotes around specifiers containing environment markers in requirement files.

A few example URL-based requirement specifiers:

    pip @ https://github.com/pypa/pip/archive/22.0.2.zip
    requests [security] @ https://github.com/psf/requests/archive/refs/heads/main.zip ; python_version >= "3.11"