Deduplicate pip show output in Requires field

news/12165.bugfix.rst

@@ -0,0 +1 @@
+This change will deduplicate entries in the ``Requires`` field of ``pip show``.

src/pip/_internal/commands/show.py

@@ -100,7 +100,11 @@ def _get_requiring_packages(current_dist: BaseDistribution) -> Iterator[str]:
         except KeyError:
             continue
 
-        requires = sorted((req.name for req in dist.iter_dependencies()), key=str.lower)
+        requires = sorted(
+            # Avoid duplicates in requirements (e.g. due to environment markers).
+            {req.name for req in dist.iter_dependencies()},
+            key=str.lower,
+        )
         required_by = sorted(_get_requiring_packages(dist), key=str.lower)
 
         try:

tests/functional/test_show.py

@@ -350,3 +350,29 @@ def test_show_include_work_dir_pkg(script: PipTestEnvironment) -> None:
     result = script.pip("show", "simple", cwd=pkg_path)
     lines = result.stdout.splitlines()
     assert "Name: simple" in lines
+
+
+def test_show_deduplicate_requirements(script: PipTestEnvironment) -> None:
+    """
+    Test that show should deduplicate requirements
+    for a package
+    """
+
+    # Create a test package and create .egg-info dir
+    pkg_path = create_test_package_with_setup(
+        script,
+        name="simple",
+        version="1.0",
+        install_requires=[
+            "pip >= 19.0.1",
+            'pip >= 19.3.1; python_version < "3.8"',
+            'pip >= 23.0.1; python_version < "3.9"',
+        ],
+    )
+    script.run("python", "setup.py", "egg_info", expect_stderr=True, cwd=pkg_path)
+
+    script.environ.update({"PYTHONPATH": pkg_path})
+
+    result = script.pip("show", "simple", cwd=pkg_path)
+    lines = result.stdout.splitlines()
+    assert "Requires: pip" in lines