Can I use `pip` instead of `easy_install` for `python setup.py install` dependency resolution?

Replacing easy_install with pip for python setup.py install Dependencies

Explore how pip can effectively manage dependencies for setup.py install and understand the historical context of easy_install.

For many years, easy_install was the go-to tool for installing Python packages. However, with the advent of pip, the Python packaging landscape significantly evolved. While easy_install could handle dependencies when running python setup.py install, pip has emerged as the preferred and more robust solution. This article delves into how pip can be used for dependency resolution in this context, the reasons behind its superiority, and best practices for modern Python development.

The Role of easy_install and Its Limitations

easy_install was part of the setuptools project and was one of the earliest tools to provide automated package installation and dependency resolution for Python. When you ran python setup.py install, setuptools would often invoke easy_install internally to fetch and install any declared dependencies. While revolutionary for its time, easy_install had several drawbacks:

• No uninstallation: It lacked a straightforward way to uninstall packages.
• No package integrity checks: It didn't verify package integrity (e.g., using hashes).
• Limited dependency resolution: Its dependency resolver was less sophisticated than pip's, sometimes leading to conflicts.
• Direct installation of eggs: It primarily installed packages as .egg files, which were less flexible than pip's wheel-based installations.

flowchart TD
    A[User runs `python setup.py install`]
    B{`setuptools` processes `setup.py`}
    C{Are there dependencies?}
    D[Invoke `easy_install` (Historically)]
    E[Fetch and install dependencies]
    F[Install main package]
    G[Installation Complete]

    A --> B
    B --> C
    C -- Yes --> D
    D --> E
    E --> F
    C -- No --> F
    F --> G

Historical Dependency Resolution Flow with easy_install

Transitioning to pip for Dependency Management

pip is the de facto standard package installer for Python. It addresses many of easy_install's shortcomings and offers a more reliable and feature-rich experience. While pip is primarily used for installing packages from PyPI or other sources, it also plays a crucial role in managing dependencies for local projects, including those using setup.py.

When you run python setup.py install, setuptools will still handle the installation of your project. However, for its dependencies, setuptools is now much more likely to use pip internally or recommend its use. The modern approach is to declare dependencies in setup.py (or pyproject.toml) and then use pip to install the project in 'editable' mode or directly from the source directory, which allows pip to handle all dependency resolution.

# setup.py example with dependencies
from setuptools import setup, find_packages

setup(
    name='my_project',
    version='0.1.0',
    packages=find_packages(),
    install_requires=[
        'requests>=2.20.0',
        'numpy',
        'pandas'
    ],
    # ... other metadata
)

Example setup.py declaring install_requires.

Modern Dependency Resolution with pip

Instead of relying on setup.py to implicitly invoke easy_install or pip for dependencies, the recommended workflow is to explicitly use pip to install your project and its dependencies. This gives you more control and leverages pip's advanced features.

Here's how pip handles dependencies for a project with a setup.py file:

1. pip install .: When you run pip install . (or pip install -e . for editable mode) in a directory containing setup.py, pip reads the install_requires (and potentially setup_requires, tests_require, etc.) from your setup.py.
2. Dependency Resolution: pip then uses its sophisticated dependency resolver to determine the correct versions of all required packages, avoiding conflicts where possible.
3. Installation: pip downloads and installs these dependencies (usually as wheels) into your Python environment.
4. Project Installation: Finally, pip installs your project itself, either as a wheel or in editable mode, ensuring all dependencies are met.

flowchart TD
    A[User runs `pip install .`]
    B{`pip` reads `setup.py` (or `pyproject.toml`)}
    C[Identify `install_requires`]
    D[Resolve dependencies (using `pip`'s resolver)]
    E[Download and install dependencies]
    F[Install main project]
    G[Installation Complete]

    A --> B
    B --> C
    C --> D
    D --> E
    E --> F
    F --> G

Modern Dependency Resolution Flow with pip

# Install your project and its dependencies using pip
pip install .

# Install your project in editable mode (for development)
pip install -e .

Using pip to install a local project and its dependencies.