Fix python buildenv dockerfile name (#4742)

Author: liliankasem

release_notes.md

@@ -15,3 +15,4 @@
    prompt the user to select which target framework to use for the Dockerfile.
 - Enhanced dotnet installation discovery by adopting the same `Muxer` logic used by the .NET SDK itself (#4732)
 - Update .NET templates package version to 4.0.5337 (#4728)
+- Fix `func pack --build-native-deps` failure on Windows for Python 3.13+ (#4742)

src/Cli/func/Helpers/PythonHelpers.cs

@@ -564,10 +564,11 @@ private static async Task<DockerImageInfo> ChoosePythonBuildEnvImage()
             {
                 // Setup image tag and content
                 string imageContent = image;
-                image = $"azure-functions/python:4-python{workerInfo.Major}.{workerInfo.Minor}-buildenv";
+                string dockerfileName = $"4-python{workerInfo.Major}{workerInfo.Minor}-buildenv";
+                image = $"azure-functions/python:{dockerfileName}";
 
                 // Prepare temporary directory for docker build context
-                string tempDockerfileDirecotry = Path.Combine(Path.GetTempPath(), $"{image}-docker");
+                string tempDockerfileDirecotry = Path.Combine(Path.GetTempPath(), $"{dockerfileName}");
                 FileSystemHelpers.EnsureDirectory(tempDockerfileDirecotry);
                 string tempDockerfile = Path.Combine(tempDockerfileDirecotry, "Dockerfile");
 

test/Cli/Func.UnitTests/HelperTests/PythonHelperTests.cs

@@ -91,6 +91,29 @@ public void AssertPythonVersion(string pythonVersion, bool expectException)
                 Assert.Throws<CliException>(() => PythonHelpers.AssertPythonVersion(worker));
             }
         }
+
+        [Theory]
+        [InlineData(3, 10)]
+        [InlineData(3, 11)]
+        [InlineData(3, 12)]
+        [InlineData(3, 13)]
+        [InlineData(3, 14)]
+        public void DockerfileNameShouldNotContainInvalidCharacters(int major, int minor)
+        {
+            // Verify the dockerfile name format matches what's used in ChoosePythonBuildEnvImage
+            // The format should be "4-python{major}{minor}-buildenv" with no colons or other invalid chars
+            string dockerfileName = $"4-python{major}{minor}-buildenv";
+
+            // Ensure no colons (invalid on Windows file paths)
+            Assert.DoesNotContain(":", dockerfileName);
+
+            // Ensure no other invalid Windows path characters
+            char[] invalidChars = Path.GetInvalidFileNameChars();
+            Assert.DoesNotContain(dockerfileName, c => invalidChars.Contains(c));
+
+            // Verify expected format
+            Assert.Matches(@"^4-python\d+-buildenv$", dockerfileName);
+        }
     }
 
     public sealed class SkipIfPythonNonExistFact : FactAttribute