Source code for pip._internal.resolution.legacy.resolver

"""Dependency Resolution

The dependency resolution in pip is performed as follows:

for top-level requirements:
    a. only one spec allowed per project, regardless of conflicts or not.
       otherwise a "double requirement" exception is raised
    b. they override sub-dependency requirements.
for sub-dependencies
    a. "first found, wins" (where the order is breadth first)

# The following comment should be removed at some point in the future.
# mypy: strict-optional=False
# mypy: disallow-untyped-defs=False

import logging
import sys
from collections import defaultdict
from itertools import chain

from pip._vendor.packaging import specifiers

from pip._internal.exceptions import (
from pip._internal.req.req_install import check_invalid_constraint_type
from pip._internal.req.req_set import RequirementSet
from pip._internal.resolution.base import BaseResolver
from pip._internal.utils.compatibility_tags import get_supported
from pip._internal.utils.logging import indent_log
from pip._internal.utils.misc import dist_in_usersite, normalize_version_info
from pip._internal.utils.packaging import (
from pip._internal.utils.typing import MYPY_CHECK_RUNNING

    from typing import DefaultDict, List, Optional, Set, Tuple
    from pip._vendor import pkg_resources

    from pip._internal.cache import WheelCache
    from pip._internal.distributions import AbstractDistribution
    from pip._internal.index.package_finder import PackageFinder
    from import Link
    from pip._internal.operations.prepare import RequirementPreparer
    from pip._internal.req.req_install import InstallRequirement
    from pip._internal.resolution.base import InstallRequirementProvider

    DiscoveredDependencies = DefaultDict[str, List[InstallRequirement]]

logger = logging.getLogger(__name__)

def _check_dist_requires_python(
    dist,  # type: pkg_resources.Distribution
    version_info,  # type: Tuple[int, int, int]
    ignore_requires_python=False,  # type: bool
    # type: (...) -> None
    Check whether the given Python version is compatible with a distribution's
    "Requires-Python" value.

    :param version_info: A 3-tuple of ints representing the Python
        major-minor-micro version to check.
    :param ignore_requires_python: Whether to ignore the "Requires-Python"
        value if the given Python version isn't compatible.

    :raises UnsupportedPythonVersion: When the given Python version isn't
    requires_python = get_requires_python(dist)
        is_compatible = check_requires_python(
            requires_python, version_info=version_info,
    except specifiers.InvalidSpecifier as exc:
            "Package %r has an invalid Requires-Python: %s",
            dist.project_name, exc,

    if is_compatible:

    version = '.'.join(map(str, version_info))
    if ignore_requires_python:
            'Ignoring failed Requires-Python check for package %r: '
            '%s not in %r',
            dist.project_name, version, requires_python,

    raise UnsupportedPythonVersion(
        'Package {!r} requires a different Python: {} not in {!r}'.format(
            dist.project_name, version, requires_python,

[docs]class Resolver(BaseResolver): """Resolves which packages need to be installed/uninstalled to perform \ the requested operation without breaking the requirements of any package. """ _allowed_strategies = {"eager", "only-if-needed", "to-satisfy-only"} def __init__( self, preparer, # type: RequirementPreparer finder, # type: PackageFinder wheel_cache, # type: Optional[WheelCache] make_install_req, # type: InstallRequirementProvider use_user_site, # type: bool ignore_dependencies, # type: bool ignore_installed, # type: bool ignore_requires_python, # type: bool force_reinstall, # type: bool upgrade_strategy, # type: str py_version_info=None, # type: Optional[Tuple[int, ...]] ): # type: (...) -> None super(Resolver, self).__init__() assert upgrade_strategy in self._allowed_strategies if py_version_info is None: py_version_info = sys.version_info[:3] else: py_version_info = normalize_version_info(py_version_info) self._py_version_info = py_version_info self.preparer = preparer self.finder = finder self.wheel_cache = wheel_cache self.upgrade_strategy = upgrade_strategy self.force_reinstall = force_reinstall self.ignore_dependencies = ignore_dependencies self.ignore_installed = ignore_installed self.ignore_requires_python = ignore_requires_python self.use_user_site = use_user_site self._make_install_req = make_install_req self._discovered_dependencies = \ defaultdict(list) # type: DiscoveredDependencies
[docs] def resolve(self, root_reqs, check_supported_wheels): # type: (List[InstallRequirement], bool) -> RequirementSet """Resolve what operations need to be done As a side-effect of this method, the packages (and their dependencies) are downloaded, unpacked and prepared for installation. This preparation is done by ``pip.operations.prepare``. Once PyPI has static dependency metadata available, it would be possible to move the preparation to become a step separated from dependency resolution. """ requirement_set = RequirementSet( check_supported_wheels=check_supported_wheels ) for req in root_reqs: if req.constraint: check_invalid_constraint_type(req) requirement_set.add_requirement(req) # Actually prepare the files, and collect any exceptions. Most hash # exceptions cannot be checked ahead of time, because # _populate_link() needs to be called before we can make decisions # based on link type. discovered_reqs = [] # type: List[InstallRequirement] hash_errors = HashErrors() for req in chain(requirement_set.all_requirements, discovered_reqs): try: discovered_reqs.extend(self._resolve_one(requirement_set, req)) except HashError as exc: exc.req = req hash_errors.append(exc) if hash_errors: raise hash_errors return requirement_set
[docs] def _is_upgrade_allowed(self, req): # type: (InstallRequirement) -> bool if self.upgrade_strategy == "to-satisfy-only": return False elif self.upgrade_strategy == "eager": return True else: assert self.upgrade_strategy == "only-if-needed" return req.user_supplied or req.constraint
[docs] def _set_req_to_reinstall(self, req): # type: (InstallRequirement) -> None """ Set a requirement to be installed. """ # Don't uninstall the conflict if doing a user install and the # conflict is not a user install. if not self.use_user_site or dist_in_usersite(req.satisfied_by): req.should_reinstall = True req.satisfied_by = None
[docs] def _check_skip_installed(self, req_to_install): # type: (InstallRequirement) -> Optional[str] """Check if req_to_install should be skipped. This will check if the req is installed, and whether we should upgrade or reinstall it, taking into account all the relevant user options. After calling this req_to_install will only have satisfied_by set to None if the req_to_install is to be upgraded/reinstalled etc. Any other value will be a dist recording the current thing installed that satisfies the requirement. Note that for vcs urls and the like we can't assess skipping in this routine - we simply identify that we need to pull the thing down, then later on it is pulled down and introspected to assess upgrade/ reinstalls etc. :return: A text reason for why it was skipped, or None. """ if self.ignore_installed: return None req_to_install.check_if_exists(self.use_user_site) if not req_to_install.satisfied_by: return None if self.force_reinstall: self._set_req_to_reinstall(req_to_install) return None if not self._is_upgrade_allowed(req_to_install): if self.upgrade_strategy == "only-if-needed": return 'already satisfied, skipping upgrade' return 'already satisfied' # Check for the possibility of an upgrade. For link-based # requirements we have to pull the tree down and inspect to assess # the version #, so it's handled way down. if not try: self.finder.find_requirement(req_to_install, upgrade=True) except BestVersionAlreadyInstalled: # Then the best version is installed. return 'already up-to-date' except DistributionNotFound: # No distribution found, so we squash the error. It will # be raised later when we re-try later to do the install. # Why don't we just raise here? pass self._set_req_to_reinstall(req_to_install) return None
[docs] def _get_abstract_dist_for(self, req): # type: (InstallRequirement) -> AbstractDistribution """Takes a InstallRequirement and returns a single AbstractDist \ representing a prepared variant of the same. """ if req.editable: return self.preparer.prepare_editable_requirement(req) # satisfied_by is only evaluated by calling _check_skip_installed, # so it must be None here. assert req.satisfied_by is None skip_reason = self._check_skip_installed(req) if req.satisfied_by: return self.preparer.prepare_installed_requirement( req, skip_reason ) # We eagerly populate the link, since that's our "legacy" behavior. self._populate_link(req) abstract_dist = self.preparer.prepare_linked_requirement(req) # NOTE # The following portion is for determining if a certain package is # going to be re-installed/upgraded or not and reporting to the user. # This should probably get cleaned up in a future refactor. # req.req is only avail after unpack for URL # pkgs repeat check_if_exists to uninstall-on-upgrade # (#14) if not self.ignore_installed: req.check_if_exists(self.use_user_site) if req.satisfied_by: should_modify = ( self.upgrade_strategy != "to-satisfy-only" or self.force_reinstall or self.ignore_installed or == 'file' ) if should_modify: self._set_req_to_reinstall(req) else: 'Requirement already satisfied (use --upgrade to upgrade):' ' %s', req, ) return abstract_dist
[docs] def _resolve_one( self, requirement_set, # type: RequirementSet req_to_install, # type: InstallRequirement ): # type: (...) -> List[InstallRequirement] """Prepare a single requirements file. :return: A list of additional InstallRequirements to also install. """ # Tell user what we are doing for this requirement: # obtain (editable), skipping, processing (local url), collecting # (remote url or package name) if req_to_install.constraint or req_to_install.prepared: return [] req_to_install.prepared = True abstract_dist = self._get_abstract_dist_for(req_to_install) # Parse and return dependencies dist = abstract_dist.get_pkg_resources_distribution() # This will raise UnsupportedPythonVersion if the given Python # version isn't compatible with the distribution's Requires-Python. _check_dist_requires_python( dist, version_info=self._py_version_info, ignore_requires_python=self.ignore_requires_python, ) more_reqs = [] # type: List[InstallRequirement] def add_req(subreq, extras_requested): sub_install_req = self._make_install_req( str(subreq), req_to_install, ) parent_req_name = to_scan_again, add_to_parent = requirement_set.add_requirement( sub_install_req, parent_req_name=parent_req_name, extras_requested=extras_requested, ) if parent_req_name and add_to_parent: self._discovered_dependencies[parent_req_name].append( add_to_parent ) more_reqs.extend(to_scan_again) with indent_log(): # We add req_to_install before its dependencies, so that we # can refer to it when adding dependencies. if not requirement_set.has_requirement( # 'unnamed' requirements will get added here # 'unnamed' requirements can only come from being directly # provided by the user. assert req_to_install.user_supplied requirement_set.add_requirement( req_to_install, parent_req_name=None, ) if not self.ignore_dependencies: if req_to_install.extras: logger.debug( "Installing extra requirements: %r", ','.join(req_to_install.extras), ) missing_requested = sorted( set(req_to_install.extras) - set(dist.extras) ) for missing in missing_requested: logger.warning( "%s does not provide the extra '%s'", dist, missing ) available_requested = sorted( set(dist.extras) & set(req_to_install.extras) ) for subreq in dist.requires(available_requested): add_req(subreq, extras_requested=available_requested) if not req_to_install.editable and not req_to_install.satisfied_by: # XXX: --no-install leads this to report 'Successfully # downloaded' for only non-editable reqs, even though we took # action on them. req_to_install.successfully_downloaded = True return more_reqs
[docs] def get_installation_order(self, req_set): # type: (RequirementSet) -> List[InstallRequirement] """Create the installation order. The installation order is topological - requirements are installed before the requiring thing. We break cycles at an arbitrary point, and make no other guarantees. """ # The current implementation, which we may change at any point # installs the user specified things in the order given, except when # dependencies must come earlier to achieve topological order. order = [] ordered_reqs = set() # type: Set[InstallRequirement] def schedule(req): if req.satisfied_by or req in ordered_reqs: return if req.constraint: return ordered_reqs.add(req) for dep in self._discovered_dependencies[]: schedule(dep) order.append(req) for install_req in req_set.requirements.values(): schedule(install_req) return order