fix populate python constraints from markers

src/poetry/core/factory.py

@@ -243,6 +243,7 @@ def create_dependency(
         from poetry.core.packages.file_dependency import FileDependency
         from poetry.core.packages.url_dependency import URLDependency
         from poetry.core.packages.utils.utils import create_nested_marker
+        from poetry.core.packages.utils.utils import get_python_constraint_from_marker
         from poetry.core.packages.vcs_dependency import VCSDependency
         from poetry.core.semver.helpers import parse_constraint
         from poetry.core.version.markers import AnyMarker
@@ -366,6 +367,10 @@ def create_dependency(
                     )
             else:
                 marker = parse_marker(markers)
+                # possibility that python constraint appears in markers, not keywords
+                if not python_versions and markers:
+                    python_versions_marker = get_python_constraint_from_marker(marker)
+                    python_versions = python_versions_marker
 
             if not marker.is_any():
                 dependency.marker = marker

tests/test_factory.py

@@ -231,3 +231,13 @@ def test_create_poetry_fails_with_invalid_dev_dependencies_iff_with_dev_is_true(
     Factory().create_poetry(
         fixtures_dir / "project_with_invalid_dev_deps", with_groups=False
     )
+
+
+def test_create_dependency_python_constraint_populated_from_markers():
+    constraint = {
+        "version": "1.2.3.",
+        "markers": 'python_version=="3.8" and sys_platform=="linux"',
+    }
+    dependency = Factory().create_dependency("a", constraint)
+
+    assert str(dependency._python_constraint) == ">=3.8,<3.9"