simplify python_version markers

src/poetry/core/version/markers.py

@@ -414,6 +414,13 @@ def __init__(
                     glue = " || "
 
                 constraint_string = glue.join(versions)
+            elif name == "python_full_version" and not swapped_name_value:
+                # fix precision of python_full_version marker
+                precision = self._value.count(".") + 1
+                if precision < 3:
+                    suffix = ".0" * (3 - precision)
+                    self._value += suffix
+                    constraint_string += suffix
         else:
             # if we have a in/not in operator we split the constraint
             # into a union/multi-constraint of single constraint
@@ -1170,6 +1177,25 @@ def _merge_single_markers(
         for c in result_constraint.constraints
     ):
         result_marker = AtomicMultiMarker(marker1.name, result_constraint)
+    elif marker1.name == "python_version":
+        from poetry.core.packages.utils.utils import get_python_constraint_from_marker
+
+        if isinstance(result_constraint, VersionRange) and result_constraint.min:
+            # Convert 'python_version >= "3.8" and python_version < "3.9"'
+            # to 'python_version == "3.8"'
+            candidate = parse_marker(f'{marker1.name} == "{result_constraint.min}"')
+            if get_python_constraint_from_marker(candidate) == result_constraint:
+                result_marker = candidate
+
+        elif isinstance(result_constraint, VersionUnion) and merge_class == MarkerUnion:
+            # Convert 'python_version == "3.8" or python_version >= "3.9"'
+            # to 'python_version >= "3.8"'
+            result_constraint = get_python_constraint_from_marker(marker1).union(
+                get_python_constraint_from_marker(marker2)
+            )
+            if result_constraint.is_simple():
+                result_marker = SingleMarker(marker1.name, result_constraint)
+
     return result_marker
 
 
@@ -1205,7 +1231,24 @@ def _merge_python_version_single_markers(
         # it may be sufficient to handle it here.
         marker_string = str(merged_marker)
         precision = marker_string.count(".") + 1
-        if precision < 3:
-            marker_string = marker_string[:-1] + ".0" * (3 - precision) + '"'
-            merged_marker = parse_marker(marker_string)
+        target_precision = 3
+        if precision < target_precision:
+            if merged_marker.operator in {"<", ">="}:
+                target_precision = 2
+                marker_string = marker_string.replace(
+                    "python_full_version", "python_version"
+                )
+            marker_string = (
+                marker_string[:-1] + ".0" * (target_precision - precision) + '"'
+            )
+        elif (
+            precision == target_precision
+            and merged_marker.operator in {"<", ">="}
+            and marker_string[:-1].endswith(".0")
+        ):
+            marker_string = marker_string.replace(
+                "python_full_version", "python_version"
+            )
+            marker_string = marker_string[:-3] + '"'  # drop trailing ".0"
+        merged_marker = parse_marker(marker_string)
     return merged_marker

tests/masonry/builders/test_sdist.py

@@ -108,11 +108,10 @@ def test_convert_dependencies() -> None:
     main = ["B>=1.0,<1.1"]
 
     extra_python = (
-        ':python_version >= "2.7" and python_version < "2.8" '
-        'or python_version >= "3.6" and python_version < "4.0"'
+        ':python_version == "2.7" or python_version >= "3.6" and python_version < "4.0"'
     )
     extra_d_dependency = (
-        'baz:python_version >= "2.7" and python_version < "2.8" '
+        'baz:python_version == "2.7" '
         'or python_version >= "3.4" and python_version < "4.0"'
     )
     extras = {extra_python: ["C==1.2.3"], extra_d_dependency: ["D==3.4.5"]}

tests/packages/test_dependency.py

@@ -55,7 +55,7 @@ def test_to_pep_508() -> None:
     result = dependency.to_pep_508()
     assert (
         result == "Django (>=1.23,<2.0) ; "
-        'python_version >= "2.7" and python_version < "2.8" '
+        'python_version == "2.7" '
         'or python_version >= "3.6" and python_version < "4.0"'
     )
 
@@ -88,7 +88,7 @@ def test_to_pep_508_in_extras() -> None:
     assert (
         result == "Django (>=1.23,<2.0) ; "
         "("
-        'python_version >= "2.7" and python_version < "2.8" '
+        'python_version == "2.7" '
         'or python_version >= "3.6" and python_version < "4.0"'
         ") "
         'and (extra == "foo" or extra == "bar")'
@@ -97,7 +97,7 @@ def test_to_pep_508_in_extras() -> None:
     result = dependency.to_pep_508(with_extras=False)
     assert (
         result == "Django (>=1.23,<2.0) ; "
-        'python_version >= "2.7" and python_version < "2.8" '
+        'python_version == "2.7" '
         'or python_version >= "3.6" and python_version < "4.0"'
     )
 

tests/packages/test_main.py

@@ -176,11 +176,8 @@ def test_dependency_from_pep_508_with_python_version_union_of_multi() -> None:
     assert dep.name == "requests"
     assert str(dep.constraint) == "2.18.0"
     assert dep.extras == frozenset()
-    assert dep.python_versions == ">=2.7 <2.8 || >=3.4 <3.5"
-    assert (
-        str(dep.marker) == 'python_version >= "2.7" and python_version < "2.8" '
-        'or python_version >= "3.4" and python_version < "3.5"'
-    )
+    assert dep.python_versions == "~2.7 || ~3.4"
+    assert str(dep.marker) == 'python_version == "2.7" or python_version == "3.4"'
 
 
 def test_dependency_from_pep_508_with_not_in_op_marker() -> None:
@@ -294,9 +291,9 @@ def test_dependency_from_pep_508_with_python_full_version() -> None:
     assert dep.name == "requests"
     assert str(dep.constraint) == "2.18.0"
     assert dep.extras == frozenset()
-    assert dep.python_versions == ">=2.7 <2.8 || >=3.4.0 <3.5.4"
+    assert dep.python_versions == "~2.7 || >=3.4.0 <3.5.4"
     assert (
-        str(dep.marker) == 'python_version >= "2.7" and python_version < "2.8" '
+        str(dep.marker) == 'python_version == "2.7" '
         'or python_full_version >= "3.4.0" and python_full_version < "3.5.4"'
     )
 

tests/version/test_markers.py

@@ -171,11 +171,24 @@ def test_single_marker_intersect() -> None:
     assert str(intersection) == 'python_version >= "3.4" and python_version < "3.6"'
 
 
-def test_single_marker_intersect_compacts_constraints() -> None:
-    m = parse_marker('python_version < "3.6"')
+@pytest.mark.parametrize(
+    ("marker1", "marker2", "expected"),
+    [
+        ('python_version < "3.6"', 'python_version < "3.4"', 'python_version < "3.4"'),
+        (
+            'python_version >= "3.6"',
+            'python_version < "3.7"',
+            'python_version == "3.6"',
+        ),
+    ],
+)
+def test_single_marker_intersect_is_single_marker(
+    marker1: str, marker2: str, expected: str
+) -> None:
+    m = parse_marker(marker1)
 
-    intersection = m.intersect(parse_marker('python_version < "3.4"'))
-    assert str(intersection) == 'python_version < "3.4"'
+    intersection = m.intersect(parse_marker(marker2))
+    assert str(intersection) == expected
 
 
 def test_single_marker_intersect_with_multi() -> None:
@@ -394,6 +407,11 @@ def test_single_marker_union_is_any() -> None:
             'python_version > "3.6"',
             'python_version != "3.6"',
         ),
+        (
+            'python_version == "3.6"',
+            'python_version >= "3.7"',
+            'python_version >= "3.6"',
+        ),
     ],
 )
 def test_single_marker_union_is_single_marker(
@@ -802,35 +820,65 @@ def test_multi_marker_union_multi_is_multi(
         (
             'python_version >= "3.6" and python_full_version < "3.6.2"',
             'python_version >= "3.6" and python_version < "3.7"',
-            'python_version >= "3.6" and python_version < "3.7"',
+            'python_version == "3.6"',
+        ),
+        (
+            'python_version >= "3.6" and python_full_version < "3.7.2"',
+            'python_version >= "3.6" and python_version < "3.8"',
+            'python_version >= "3.6" and python_version < "3.8"',
         ),
         (
             'python_version > "3.6" and python_full_version < "3.6.2"',
             'python_version > "3.6" and python_version < "3.7"',
             'python_version > "3.6" and python_version < "3.7"',
         ),
+        (
+            'python_version > "3.6" and python_full_version < "3.7.2"',
+            'python_version > "3.6" and python_version < "3.8"',
+            'python_version > "3.6" and python_version < "3.8"',
+        ),
         # Ranges meet exactly
         (
             'python_version >= "3.6" and python_full_version < "3.6.2"',
             'python_full_version >= "3.6.2" and python_version < "3.7"',
-            'python_version >= "3.6" and python_version < "3.7"',
+            'python_version == "3.6"',
+        ),
+        (
+            'python_version >= "3.6" and python_full_version < "3.7.2"',
+            'python_full_version >= "3.6.2" and python_version < "3.8"',
+            'python_version >= "3.6" and python_version < "3.8"',
         ),
         (
             'python_version >= "3.6" and python_full_version <= "3.6.2"',
             'python_full_version > "3.6.2" and python_version < "3.7"',
-            'python_version >= "3.6" and python_version < "3.7"',
+            'python_version == "3.6"',
+        ),
+        (
+            'python_version >= "3.6" and python_full_version <= "3.7.2"',
+            'python_full_version > "3.6.2" and python_version < "3.8"',
+            'python_version >= "3.6" and python_version < "3.8"',
         ),
         # Ranges overlap
         (
             'python_version >= "3.6" and python_full_version <= "3.6.8"',
             'python_full_version >= "3.6.2" and python_version < "3.7"',
-            'python_version >= "3.6" and python_version < "3.7"',
+            'python_version == "3.6"',
+        ),
+        (
+            'python_version >= "3.6" and python_full_version <= "3.7.8"',
+            'python_full_version >= "3.6.2" and python_version < "3.8"',
+            'python_version >= "3.6" and python_version < "3.8"',
         ),
         # Ranges with same end.
         (
             'python_version >= "3.6" and python_version < "3.7"',
             'python_full_version >= "3.6.2" and python_version < "3.7"',
-            'python_version >= "3.6" and python_version < "3.7"',
+            'python_version == "3.6"',
+        ),
+        (
+            'python_version >= "3.6" and python_version < "3.8"',
+            'python_full_version >= "3.6.2" and python_version < "3.8"',
+            'python_version >= "3.6" and python_version < "3.8"',
         ),
         (
             'python_version >= "3.6" and python_version <= "3.7"',
@@ -984,8 +1032,7 @@ def test_marker_union_intersect_marker_union_drops_unnecessary_markers() -> None
 
     intersection = m.intersect(m2)
     expected = (
-        'python_version >= "2.7" and python_version < "2.8" '
-        'or python_version >= "3.4" and python_version < "4.0"'
+        'python_version == "2.7" or python_version >= "3.4" and python_version < "4.0"'
     )
     assert str(intersection) == expected
 
@@ -1358,10 +1405,7 @@ def test_without_extras(marker: str, expected: str) -> None:
                 ' and extra == "foo"'
             ),
             "extra",
-            (
-                'python_version >= "2.7" and python_version < "2.8"'
-                ' or python_version >= "3.7" and python_version < "3.8"'
-            ),
+            ('python_version == "2.7" or python_version == "3.7"'),
         ),
     ],
 )
@@ -2052,8 +2096,8 @@ def test_complex_union() -> None:
     ]
     assert (
         str(union(*markers))
-        == 'platform_system == "Darwin" and platform_machine == "arm64"'
-        ' and python_version >= "3.6" or python_version >= "3.10"'
+        == 'python_version >= "3.6" and platform_system == "Darwin"'
+        ' and platform_machine == "arm64" or python_version >= "3.10"'
     )
 
 
@@ -2085,8 +2129,8 @@ def test_complex_intersection() -> None:
     ]
     assert (
         str(dnf(intersection(*markers).invert()))
-        == 'platform_system == "Darwin" and platform_machine == "arm64"'
-        ' and python_version >= "3.6" or python_version >= "3.10"'
+        == 'python_version >= "3.6" and platform_system == "Darwin"'
+        ' and platform_machine == "arm64" or python_version >= "3.10"'
     )
 
 
@@ -2132,14 +2176,14 @@ def test_intersection_avoids_combinatorial_explosion() -> None:
     )
     assert (
         str(m1.intersect(m2))
-        == 'python_full_version >= "3.11.0" and python_full_version < "4.0.0"'
+        == 'python_version >= "3.11" and python_full_version < "4.0.0"'
         ' and (platform_machine == "aarch64" or platform_machine == "ppc64le"'
         ' or platform_machine == "x86_64" or platform_machine == "amd64"'
         ' or platform_machine == "AMD64" or platform_machine == "win32"'
         ' or platform_machine == "WIN32")'
     )
     assert (
-        str(m2.intersect(m1)) == 'python_full_version >= "3.11.0"'
+        str(m2.intersect(m1)) == 'python_version >= "3.11"'
         ' and (platform_machine == "aarch64" or platform_machine == "ppc64le"'
         ' or platform_machine == "x86_64" or platform_machine == "amd64"'
         ' or platform_machine == "AMD64" or platform_machine == "win32"'
@@ -2222,20 +2266,20 @@ def test_intersection_avoids_combinatorial_explosion() -> None:
         ('== "3.6"', '> "3.5.2"', '== "3.6"', '> "3.5.2"'),
         ('== "3.6"', '>= "3.5.2"', '== "3.6"', '>= "3.5.2"'),
         ('== "3.6"', '!= "3.5.2"', '== "3.6"', '!= "3.5.2"'),
-        ('== "3.6"', '< "3.6.0"', EMPTY, '< "3.7.0"'),
-        ('== "3.6"', '<= "3.6.0"', '== "3.6.0"', '< "3.7.0"'),
-        ('== "3.6"', '> "3.6.0"', None, '>= "3.6.0"'),
-        ('== "3.6"', '>= "3.6.0"', '== "3.6"', '>= "3.6.0"'),
+        ('== "3.6"', '< "3.6.0"', EMPTY, '< "3.7"'),
+        ('== "3.6"', '<= "3.6.0"', '== "3.6.0"', '< "3.7"'),
+        ('== "3.6"', '> "3.6.0"', None, '>= "3.6"'),
+        ('== "3.6"', '>= "3.6.0"', '== "3.6"', '>= "3.6"'),
         ('== "3.6"', '!= "3.6.0"', None, ""),
-        ('== "3.6"', '< "3.6.1"', None, '< "3.7.0"'),
-        ('== "3.6"', '<= "3.6.1"', None, '< "3.7.0"'),
-        ('== "3.6"', '> "3.6.1"', None, '>= "3.6.0"'),
-        ('== "3.6"', '>= "3.6.1"', None, '>= "3.6.0"'),
+        ('== "3.6"', '< "3.6.1"', None, '< "3.7"'),
+        ('== "3.6"', '<= "3.6.1"', None, '< "3.7"'),
+        ('== "3.6"', '> "3.6.1"', None, '>= "3.6"'),
+        ('== "3.6"', '>= "3.6.1"', None, '>= "3.6"'),
         ('== "3.6"', '!= "3.6.1"', None, ""),
-        ('== "3.6"', '< "3.7.0"', '== "3.6"', '< "3.7.0"'),
+        ('== "3.6"', '< "3.7.0"', '== "3.6"', '< "3.7"'),
         ('== "3.6"', '<= "3.7.0"', '== "3.6"', '<= "3.7.0"'),
         ('== "3.6"', '> "3.7.0"', EMPTY, None),
-        ('== "3.6"', '>= "3.7.0"', EMPTY, '>= "3.6.0"'),
+        ('== "3.6"', '>= "3.7.0"', EMPTY, '>= "3.6"'),
         ('== "3.6"', '!= "3.7.0"', '== "3.6"', '!= "3.7.0"'),
         ('== "3.6"', '<= "3.7.1"', '== "3.6"', '<= "3.7.1"'),
         ('== "3.6"', '< "3.7.1"', '== "3.6"', '< "3.7.1"'),
@@ -2249,20 +2293,20 @@ def test_intersection_avoids_combinatorial_explosion() -> None:
         ('!= "3.6"', '> "3.5.2"', None, ""),
         ('!= "3.6"', '>= "3.5.2"', None, ""),
         ('!= "3.6"', '!= "3.5.2"', None, ""),
-        ('!= "3.6"', '< "3.6.0"', '< "3.6.0"', '!= "3.6"'),
-        ('!= "3.6"', '<= "3.6.0"', '< "3.6.0"', None),
-        ('!= "3.6"', '> "3.6.0"', '>= "3.7.0"', '!= "3.6.0"'),
-        ('!= "3.6"', '>= "3.6.0"', '>= "3.7.0"', ""),
+        ('!= "3.6"', '< "3.6.0"', '< "3.6"', '!= "3.6"'),
+        ('!= "3.6"', '<= "3.6.0"', '< "3.6"', None),
+        ('!= "3.6"', '> "3.6.0"', '>= "3.7"', '!= "3.6.0"'),
+        ('!= "3.6"', '>= "3.6.0"', '>= "3.7"', ""),
         ('!= "3.6"', '!= "3.6.0"', '!= "3.6"', '!= "3.6.0"'),
-        ('!= "3.6"', '< "3.6.1"', '< "3.6.0"', None),
-        ('!= "3.6"', '<= "3.6.1"', '< "3.6.0"', None),
-        ('!= "3.6"', '> "3.6.1"', '>= "3.7.0"', None),
-        ('!= "3.6"', '>= "3.6.1"', '>= "3.7.0"', None),
+        ('!= "3.6"', '< "3.6.1"', '< "3.6"', None),
+        ('!= "3.6"', '<= "3.6.1"', '< "3.6"', None),
+        ('!= "3.6"', '> "3.6.1"', '>= "3.7"', None),
+        ('!= "3.6"', '>= "3.6.1"', '>= "3.7"', None),
         ('!= "3.6"', '!= "3.6.1"', '!= "3.6"', '!= "3.6.1"'),
-        ('!= "3.6"', '< "3.7.0"', '< "3.6.0"', ""),
+        ('!= "3.6"', '< "3.7.0"', '< "3.6"', ""),
         ('!= "3.6"', '<= "3.7.0"', None, ""),
         ('!= "3.6"', '> "3.7.0"', '> "3.7.0"', '!= "3.6"'),
-        ('!= "3.6"', '>= "3.7.0"', '>= "3.7.0"', '!= "3.6"'),
+        ('!= "3.6"', '>= "3.7.0"', '>= "3.7"', '!= "3.6"'),
         ('!= "3.6"', '!= "3.7.0"', None, ""),
         ('!= "3.6"', '<= "3.7.1"', None, ""),
         ('!= "3.6"', '< "3.7.1"', None, ""),

tests/version/test_requirements.py

@@ -103,10 +103,7 @@ def assert_requirement(
             {
                 "name": "foo",
                 "constraint": ">=1.2.3",
-                "marker": (
-                    'python_version >= "2.7" and python_version < "2.8" or'
-                    ' python_version >= "3.4" and python_version < "3.5"'
-                ),
+                "marker": ('python_version == "2.7" or python_version == "3.4"'),
             },
         ),
         (