installrequires

install_requires is a parameter used in Python packaging, most commonly in the setup() function of setuptools. It declares the runtime dependencies a project needs to function. When a user installs the package (for example from PyPI or from a source distribution), the packaging tool will resolve and install the listed dependencies automatically.

Usage and scope

In a setup script, install_requires is typically a list of dependency specifiers, such as ["requests>=2.20", "numpy", "pandas; python_version>='3.8'"]. The items may include version constraints and environment markers. install_requires targets runtime dependencies, not development or testing requirements, which are usually specified separately (for example in extras_require or a separate requirements file).

Version specifiers and environment markers

Dependencies can be constrained with operators like >=, <=, ==, or ~=. Environment markers allow conditional dependencies based on Python version, platform, or other factors (for example, "pywin32; sys_platform == 'win32'"). This enables projects to install only appropriate dependencies for a given environment.

Relation to extras and development needs

Extras can be used to declare optional dependencies that are not required for normal use, via extras_require and a named key (for example, "dev" or "test"). This allows users to opt into additional functionality without broadening the base installation. install_requires is not a mechanism to distinguish between development and runtime requirements; those distinctions are handled with extras or separate tooling.

Alternatives and scope

In modern Python packaging, some projects use pyproject.toml with different backends or dependency declarations (such as Poetry or PEP 621). However, install_requires remains a fundamental construct in setuptools-based projects for specifying runtime dependencies and is widely supported by packaging tools like pip.