[Python] python regex validation generation (#11525)

* fix: python regex validation generation

* docs: updated comment to be more specific

* fix: check the right value used when generating the regex

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PythonLegacyClientCodegen.java

@@ -329,13 +329,6 @@ public void postProcessPattern(String pattern, Map<String, Object> vendorExtensi
                         + "/pattern/modifiers convention. " + pattern + " is not valid.");
             }
 
-        //check for instances of extra backslash that could cause compile issues and remove
-        int firstBackslash = pattern.indexOf("\\");
-            int bracket = pattern.indexOf("[");
-            if (firstBackslash == 0 || firstBackslash == 1 || firstBackslash == bracket+1) {
-                pattern = pattern.substring(0,firstBackslash)+pattern.substring(firstBackslash+1);
-            }
-
             String regex = pattern.substring(1, i).replace("'", "\\'");
             List<String> modifiers = new ArrayList<String>();
 

modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonClientTest.java

@@ -440,6 +440,21 @@ public void testObjectWithValidations() {
         Assert.assertEquals((int) model.getMinProperties(), 1);
     }
 
+    @Test(description = "tests RegexObjects")
+    public void testRegexObjects() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/issue_11521.yaml");
+        final DefaultCodegen codegen = new PythonClientCodegen();
+        codegen.setOpenAPI(openAPI);
+
+        String modelName = "DateTimeObject";
+        Schema modelSchema = ModelUtils.getSchema(openAPI, modelName);
+        final CodegenModel model = codegen.fromModel(modelName, modelSchema);
+        final CodegenProperty property1 = model.vars.get(0);
+        Assert.assertEquals(property1.baseName, "datetime");
+        Assert.assertEquals(property1.pattern, "/[\\d]{4}-[\\d]{2}-[\\d]{2}T[\\d]{1,2}:[\\d]{2}Z/");
+        Assert.assertEquals(property1.vendorExtensions.get("x-regex"), "[\\d]{4}-[\\d]{2}-[\\d]{2}T[\\d]{1,2}:[\\d]{2}Z");
+    }
+
     @Test(description = "tests RecursiveToExample")
     public void testRecursiveToExample() throws IOException {
         final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/issue_8052_recursive_model.yaml");

modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonLegacyClientCodegenTest.java

@@ -93,7 +93,9 @@ public void testRegularExpressionOpenAPISchemaVersion3() {
         Assert.assertEquals(op.allParams.get(5).pattern, "/^pattern\\d{3}$/i");
         // pattern_with_backslash_after_bracket '/^[\pattern\d{3}$/i'
         // added to test fix for issue #6675
-        Assert.assertEquals(op.allParams.get(6).pattern, "/^[\\pattern\\d{3}$/i");
+        // removed because "/^[\\pattern\\d{3}$/i" is invalid regex because [ is not escaped and there is no closing ]
+        // Assert.assertEquals(op.allParams.get(6).pattern, "/^[\\pattern\\d{3}$/i");
+
     }
 
 

modules/openapi-generator/src/test/resources/3_0/issue_11521.yaml

@@ -0,0 +1,17 @@
+openapi: 3.0.0
+info:
+  description: a spec to test free form object models
+  version: 1.0.0
+  title: OpenAPI Petstore
+  license:
+    name: Apache-2.0
+    url: "https://www.apache.org/licenses/LICENSE-2.0.html"
+tags: []
+paths: {}
+components:
+  schemas:
+    DateTimeObject:
+      properties:
+        datetime:
+          type: string
+          pattern: '[\d]{4}-[\d]{2}-[\d]{2}T[\d]{1,2}:[\d]{2}Z'