Ignore dependency if not needed (#1789)

poetry/puzzle/provider.py

@@ -671,13 +671,16 @@ class Provider:
             raise CompatibilityError(*python_constraints)
 
         # Modifying dependencies as needed
+        clean_dependencies = []
         for dep in dependencies:
             if not package.dependency.python_constraint.is_any():
-                dep.transitive_python_versions = str(
-                    dep.python_constraint.intersect(
+                python_constraint_intersection = dep.python_constraint.intersect(
                     package.dependency.python_constraint
                 )
-                )
+                if python_constraint_intersection.is_empty():
+                    # This depencency is not needed under current python constraint.
+                    continue
+                dep.transitive_python_versions = str(python_constraint_intersection)
 
             if (package.dependency.is_directory() or package.dependency.is_file()) and (
                 dep.is_directory() or dep.is_file()
@@ -691,8 +694,9 @@ class Provider:
 
                 # TODO: Improve the way we set the correct relative path for dependencies
                 dep._path = relative
+            clean_dependencies.append(dep)
 
-        package.requires = dependencies
+        package.requires = clean_dependencies
 
         return package
 

tests/puzzle/test_solver.py

@@ -1887,3 +1887,19 @@ def test_solver_does_not_fail_with_locked_git_and_non_git_dependencies(
             {"job": "install", "package": git_package, "skipped": True},
         ],
     )
+
+
+def test_ignore_python_constraint_no_overlap_dependencies(solver, repo, package):
+    pytest = get_package("demo", "1.0.0")
+    pytest.add_dependency("configparser", {"version": "^1.2.3", "python": "<3.2"})
+
+    package.add_dependency("demo", {"version": "^1.0.0", "python": "^3.6"})
+
+    repo.add_package(pytest)
+    repo.add_package(get_package("configparser", "1.2.3"))
+
+    ops = solver.solve()
+
+    check_solver_result(
+        ops, [{"job": "install", "package": pytest}],
+    )