pypa/pip · error · InstallationError

Could not satisfy constraints for

Error message

Could not satisfy constraints for '{install_req.name}': installation from path or url cannot be constrained to a version

What it means

In the legacy resolver (resolver.py:281-289), when an existing requirement is a constraint and the new install_req is a link (path/url) whose path differs from the constraint's link, pip raises InstallationError. A path/url install cannot be constrained to a specific version because the version is whatever that path contains.

Solutions

1. Do not version-constrain path/url installs; let the path define the version.
2. Make the constraint point to the same path as the install requirement.
3. Move the version pin out of the constraints file for path-installed packages.

Example fix

# before
# constraints.txt: pkg==1.0
pip install -c constraints.txt ./local/pkg
# after
pip install ./local/pkg   # no version constraint on a path install

# Warn if a constraints file pins a version for a path/url requirement.
import re, os
reqs = [l.strip() for l in open("requirements.txt") if l.strip() and not l.startswith("-")]
cons = [l.strip() for l in open("constraints.txt") if l.strip()]
path_req_names = {
    re.match(r"([A-Za-z0-9_.-]+)", l).group(1).lower()
    for l in reqs
    if ("/" in l or os.sep in l or l.startswith(("git+", "http", "./", "..")))
}
for c in cons:
    nm = re.match(r"([A-Za-z0-9_.-]+)", c)
    if nm and nm.group(1).lower() in path_req_names and "==" in c:
        print(f"Avoid version-constraining path install: {c}")

When it happens

Trigger: Using -c constraints.txt where a package is constrained by version, while simultaneously installing that package from a local path or URL with a different path.

Common situations: Mixing version constraints (-c) with editable/VCS/path installs of the same package; constraints referencing a different source than the install.

Related errors

• Constraints cannot have extras
• Could not open file
• [dependency-groups] resolution failed for
• Double requirement given
• Editable requirements are not allowed as constraints

AI-assisted analysis of pypa/pip@f399c37189 (2026-08-08). Data as JSON: /api/errors/39dd1d953f0ff866. Report an issue: GitHub.

Appendix: source

Thrown at src/pip/_internal/resolution/legacy/resolver.py:285

            )

        # When no existing requirement exists, add the requirement as a
        # dependency and it will be scanned again after.
        if not existing_req:
            requirement_set.add_named_requirement(install_req)
            # We'd want to rescan this requirement later
            return [install_req], install_req

        # Assume there's no need to scan, and that we've already
        # encountered this for scanning.
        if install_req.constraint or not existing_req.constraint:
            return [], existing_req

        does_not_satisfy_constraint = install_req.link and not (
            existing_req.link and install_req.link.path == existing_req.link.path
        )
        if does_not_satisfy_constraint:
            raise InstallationError(
                f"Could not satisfy constraints for '{install_req.name}': "
                "installation from path or url cannot be "
                "constrained to a version"
            )
        # If we're now installing a constraint, mark the existing
        # object for real installation.
        existing_req.constraint = False
        # If we're now installing a user supplied requirement,
        # mark the existing object as such.
        if install_req.user_supplied:
            existing_req.user_supplied = True
        existing_req.extras = tuple(
            sorted(set(existing_req.extras) | set(install_req.extras))
        )
        logger.debug(
            "Setting %s extras to: %s",
            existing_req,
            existing_req.extras,

View on GitHub (pinned to f399c37189)