diff --git a/python/private/pypi/BUILD.bazel b/python/private/pypi/BUILD.bazel
index 6bfd64652e..48a1837f36 100644
--- a/python/private/pypi/BUILD.bazel
+++ b/python/private/pypi/BUILD.bazel
@@ -241,6 +241,9 @@ bzl_library(
 bzl_library(
     name = "parse_simpleapi_html_bzl",
     srcs = ["parse_simpleapi_html.bzl"],
+    deps = [
+        ":version_from_filename_bzl",
+    ],
 )
 
 bzl_library(
@@ -416,6 +419,11 @@ bzl_library(
     ],
 )
 
+bzl_library(
+    name = "version_from_filename_bzl",
+    srcs = ["version_from_filename.bzl"],
+)
+
 bzl_library(
     name = "whl_config_repo_bzl",
     srcs = ["whl_config_repo.bzl"],
diff --git a/python/private/pypi/parse_simpleapi_html.bzl b/python/private/pypi/parse_simpleapi_html.bzl
index a41f0750c4..23ecbf496f 100644
--- a/python/private/pypi/parse_simpleapi_html.bzl
+++ b/python/private/pypi/parse_simpleapi_html.bzl
@@ -16,6 +16,8 @@
 Parse SimpleAPI HTML in Starlark.
 """
 
+load(":version_from_filename.bzl", "version_from_filename")
+
 def parse_simpleapi_html(*, url, content):
     """Get the package URLs for given shas by parsing the Simple API HTML.
 
@@ -64,7 +66,7 @@ def parse_simpleapi_html(*, url, content):
 
         head, _, _ = tail.rpartition("</a>")
         maybe_metadata, _, filename = head.rpartition(">")
-        version = _version(filename)
+        version = version_from_filename(filename)
         sha256s_by_version.setdefault(version, []).append(sha256)
 
         metadata_sha256 = ""
@@ -105,28 +107,6 @@ def parse_simpleapi_html(*, url, content):
         sha256s_by_version = sha256s_by_version,
     )
 
-_SDIST_EXTS = [
-    ".tar",  # handles any compression
-    ".zip",
-]
-
-def _version(filename):
-    # See https://packaging.python.org/en/latest/specifications/binary-distribution-format/#binary-distribution-format
-
-    _, _, tail = filename.partition("-")
-    version, _, _ = tail.partition("-")
-    if version != tail:
-        # The format is {name}-{version}-{whl_specifiers}.whl
-        return version
-
-    # NOTE @aignas 2025-03-29: most of the files are wheels, so this is not the common path
-
-    # {name}-{version}.{ext}
-    for ext in _SDIST_EXTS:
-        version, _, _ = version.partition(ext)  # build or name
-
-    return version
-
 def _get_root_directory(url):
     scheme_end = url.find("://")
     if scheme_end == -1:
diff --git a/python/private/pypi/version_from_filename.bzl b/python/private/pypi/version_from_filename.bzl
new file mode 100644
index 0000000000..d0b6e3105d
--- /dev/null
+++ b/python/private/pypi/version_from_filename.bzl
@@ -0,0 +1,42 @@
+"""Parse the version of the thing just from the filename. This is useful for selecting files based on the requested version."""
+
+_SDIST_EXTS = [
+    ".tar",  # handles any compression
+    ".zip",
+]
+
+def version_from_filename(filename, _fail = None):
+    """Parse the version of the filename.
+
+    Args:
+        filename: {type}`str` the filename.
+        _fail: The fail function.
+
+    Returns:
+        A string version or None if we could not parse the version.
+    """
+    # See https://packaging.python.org/en/latest/specifications/binary-distribution-format/#binary-distribution-format
+
+    if filename.endswith(".whl"):
+        # The format is {name}-{version}-{whl_specifiers}.whl
+        _, _, version = filename.partition("-")
+        version, _, _ = version.partition("-")
+        return version
+
+    # NOTE @aignas 2025-03-29: most of the files are wheels, so this is not the common path
+
+    # {name}-{version}.{ext}
+    head = ""
+    for ext in _SDIST_EXTS:
+        head, _, _ = filename.rpartition(ext)  # build or name
+        if head:
+            break
+
+    if not head:
+        if _fail:
+            _fail("Unsupported sdist extension: {filename}".format(filename = filename))
+        return None
+
+    # Based on PEP440 the version number cannot include dashes
+    _, _, version = head.rpartition("-")
+    return version
diff --git a/tests/pypi/version_from_filename/BUILD.bazel b/tests/pypi/version_from_filename/BUILD.bazel
new file mode 100644
index 0000000000..e9d50dc6b8
--- /dev/null
+++ b/tests/pypi/version_from_filename/BUILD.bazel
@@ -0,0 +1,3 @@
+load(":version_from_filename_tests.bzl", "version_from_filename_test_suite")
+
+version_from_filename_test_suite(name = "version_from_filename_tests")
diff --git a/tests/pypi/version_from_filename/version_from_filename_tests.bzl b/tests/pypi/version_from_filename/version_from_filename_tests.bzl
new file mode 100644
index 0000000000..fab921fd4f
--- /dev/null
+++ b/tests/pypi/version_from_filename/version_from_filename_tests.bzl
@@ -0,0 +1,56 @@
+""
+
+load("@rules_testing//lib:test_suite.bzl", "test_suite")
+load("//python/private/pypi:version_from_filename.bzl", "version_from_filename")  # buildifier: disable=bzl-visibility
+
+_tests = []
+
+def _test_wheel_version_extraction(env):
+    # Case 1: wheel
+    env.expect.that_str(version_from_filename("foo-1.2.3-py3-none-any.whl")).equals("1.2.3")
+
+_tests.append(_test_wheel_version_extraction)
+
+def _test_sdist_version_extraction(env):
+    # Case 1: Standard sdist
+    env.expect.that_str(version_from_filename("foo-1.2.3.tar.gz")).equals("1.2.3")
+
+    # Case 2: PEP 625 - Project name has underscores (normalized from dashes)
+    # If the package is 'my-pkg', the sdist might be 'my_pkg-1.0.0.tar.gz'
+    env.expect.that_str(version_from_filename("my_pkg-1.0.0.tar.gz")).equals("1.0.0")
+
+    # Case 3: Project name has multiple underscores
+    env.expect.that_str(version_from_filename("very_long_project_name-0.5.0.zip")).equals("0.5.0")
+
+    # Case 4: Legacy sdist with hyphens in name
+    # Note: Modern tools normalize this, but we should support the hyphen split
+    env.expect.that_str(version_from_filename("complex-name-1.2.3.tar.gz")).equals("1.2.3")
+
+    # Case 5: Version contains an underscore (e.g. local versions)
+    env.expect.that_str(version_from_filename("pkg-1.2.3_post1.tar.gz")).equals("1.2.3_post1")
+
+    # Case 6: custom compression
+    env.expect.that_str(version_from_filename("pkg-1.2.3_post1.tar.xz")).equals("1.2.3_post1")
+
+_tests.append(_test_sdist_version_extraction)
+
+def _test_sdist_version_extraction_fail(env):
+    failures = []
+
+    # Case 1: 7z
+    env.expect.that_str(version_from_filename("foo-1.2.3.7z")).equals(None)
+    env.expect.that_str(version_from_filename("foo-1.2.3.7z", _fail = failures.append)).equals(None)
+    env.expect.that_collection(failures).contains_exactly(["Unsupported sdist extension: foo-1.2.3.7z"])
+
+    # Case 2: egg
+    failures.clear()
+    env.expect.that_str(version_from_filename("foo-1.2.3-py3.egg", _fail = failures.append)).equals(None)
+    env.expect.that_collection(failures).contains_exactly(["Unsupported sdist extension: foo-1.2.3-py3.egg"])
+
+_tests.append(_test_sdist_version_extraction_fail)
+
+def version_from_filename_test_suite(name):
+    test_suite(
+        name = name,
+        basic_tests = _tests,
+    )