From dd4647873f52dc1da8476f29734e9a91b6dd1454 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=B5=E3=81=81?= <yuki@yuki0311.com>
Date: Mon, 20 Jul 2026 06:59:54 +0000
Subject: [PATCH 1/3] [python] serialize booleans as lowercase in all parameter
 styles

parameters_to_url_query lowercased a top-level boolean query value, but
booleans inside collections went through str() and ended up as True/False
on the wire (?flags=True,False). Path, header and form parameters had no
boolean handling at all, producing /pets/True style urls. Lowercase them
in parameters_to_tuples and in the collection branches of
parameters_to_url_query as well.
---
 .../main/resources/python/api_client.mustache | 20 +++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/modules/openapi-generator/src/main/resources/python/api_client.mustache b/modules/openapi-generator/src/main/resources/python/api_client.mustache
index 71392d82e126..7d8d58f79721 100644
--- a/modules/openapi-generator/src/main/resources/python/api_client.mustache
+++ b/modules/openapi-generator/src/main/resources/python/api_client.mustache
@@ -646,10 +646,15 @@ https://github.com/OpenAPITools/openapi-generator/blob/c84b949df1a9ec04ba75989cb
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -660,7 +665,9 @@ https://github.com/OpenAPITools/openapi-generator/blob/c84b949df1a9ec04ba75989cb
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -686,7 +693,10 @@ https://github.com/OpenAPITools/openapi-generator/blob/c84b949df1a9ec04ba75989cb
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -697,7 +707,9 @@ https://github.com/OpenAPITools/openapi-generator/blob/c84b949df1a9ec04ba75989cb
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))

From b6b1894877e7c501146db298bd63fbd4b6a9e317 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=B5=E3=81=81?= <yuki@yuki0311.com>
Date: Mon, 20 Jul 2026 06:59:55 +0000
Subject: [PATCH 2/3] update samples

---
 .../openapi_client/api_client.py              | 20 +++++++++++++++----
 .../python/openapi_client/api_client.py       | 20 +++++++++++++++----
 .../legacy_model_dict_client/api_client.py    | 20 +++++++++++++++----
 .../python-aiohttp/petstore_api/api_client.py | 20 +++++++++++++++----
 .../petstore_api/api_client.py                | 20 +++++++++++++++----
 .../python-httpx/petstore_api/api_client.py   | 20 +++++++++++++++----
 .../petstore_api/api_client.py                | 20 +++++++++++++++----
 .../python/petstore_api/api_client.py         | 20 +++++++++++++++----
 8 files changed, 128 insertions(+), 32 deletions(-)

diff --git a/samples/client/echo_api/python-disallowAdditionalPropertiesIfNotPresent/openapi_client/api_client.py b/samples/client/echo_api/python-disallowAdditionalPropertiesIfNotPresent/openapi_client/api_client.py
index 594ec0e5a703..2b8dbc627dab 100644
--- a/samples/client/echo_api/python-disallowAdditionalPropertiesIfNotPresent/openapi_client/api_client.py
+++ b/samples/client/echo_api/python-disallowAdditionalPropertiesIfNotPresent/openapi_client/api_client.py
@@ -489,10 +489,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -503,7 +508,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -529,7 +536,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -540,7 +550,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/client/echo_api/python/openapi_client/api_client.py b/samples/client/echo_api/python/openapi_client/api_client.py
index 594ec0e5a703..2b8dbc627dab 100644
--- a/samples/client/echo_api/python/openapi_client/api_client.py
+++ b/samples/client/echo_api/python/openapi_client/api_client.py
@@ -489,10 +489,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -503,7 +508,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -529,7 +536,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -540,7 +550,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/client/others/python-legacy-model-dictionaries/legacy_model_dict_client/api_client.py b/samples/client/others/python-legacy-model-dictionaries/legacy_model_dict_client/api_client.py
index 37ab9efc5d92..bf9b93c745f6 100644
--- a/samples/client/others/python-legacy-model-dictionaries/legacy_model_dict_client/api_client.py
+++ b/samples/client/others/python-legacy-model-dictionaries/legacy_model_dict_client/api_client.py
@@ -597,10 +597,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -611,7 +616,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -637,7 +644,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -648,7 +658,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/openapi3/client/petstore/python-aiohttp/petstore_api/api_client.py b/samples/openapi3/client/petstore/python-aiohttp/petstore_api/api_client.py
index f90151f6105b..9b4ecfe9b20b 100644
--- a/samples/openapi3/client/petstore/python-aiohttp/petstore_api/api_client.py
+++ b/samples/openapi3/client/petstore/python-aiohttp/petstore_api/api_client.py
@@ -488,10 +488,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -502,7 +507,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -528,7 +535,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -539,7 +549,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/openapi3/client/petstore/python-httpx-sync/petstore_api/api_client.py b/samples/openapi3/client/petstore/python-httpx-sync/petstore_api/api_client.py
index 5fb082d86bc9..8e7f65530e12 100644
--- a/samples/openapi3/client/petstore/python-httpx-sync/petstore_api/api_client.py
+++ b/samples/openapi3/client/petstore/python-httpx-sync/petstore_api/api_client.py
@@ -491,10 +491,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -505,7 +510,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -531,7 +538,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -542,7 +552,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/openapi3/client/petstore/python-httpx/petstore_api/api_client.py b/samples/openapi3/client/petstore/python-httpx/petstore_api/api_client.py
index 5fb082d86bc9..8e7f65530e12 100644
--- a/samples/openapi3/client/petstore/python-httpx/petstore_api/api_client.py
+++ b/samples/openapi3/client/petstore/python-httpx/petstore_api/api_client.py
@@ -491,10 +491,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -505,7 +510,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -531,7 +538,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -542,7 +552,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/openapi3/client/petstore/python-lazyImports/petstore_api/api_client.py b/samples/openapi3/client/petstore/python-lazyImports/petstore_api/api_client.py
index a26ad3c644a2..9e14d8b2debf 100644
--- a/samples/openapi3/client/petstore/python-lazyImports/petstore_api/api_client.py
+++ b/samples/openapi3/client/petstore/python-lazyImports/petstore_api/api_client.py
@@ -488,10 +488,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -502,7 +507,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -528,7 +535,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -539,7 +549,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))
diff --git a/samples/openapi3/client/petstore/python/petstore_api/api_client.py b/samples/openapi3/client/petstore/python/petstore_api/api_client.py
index 4a91fbc24248..9abc7d7dabfd 100755
--- a/samples/openapi3/client/petstore/python/petstore_api/api_client.py
+++ b/samples/openapi3/client/petstore/python/petstore_api/api_client.py
@@ -488,10 +488,15 @@ def parameters_to_tuples(self, params, collection_formats):
         if collection_formats is None:
             collection_formats = {}
         for k, v in params.items() if isinstance(params, dict) else params:
+            if isinstance(v, bool):
+                v = str(v).lower()
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, value) for value in v)
+                    new_params.extend(
+                        (k, str(value).lower() if isinstance(value, bool) else value)
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -502,7 +507,9 @@ def parameters_to_tuples(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(str(value) for value in v)))
+                        (k, delimiter.join(
+                            str(value).lower() if isinstance(value, bool) else str(value)
+                            for value in v)))
             else:
                 new_params.append((k, v))
         return new_params
@@ -528,7 +535,10 @@ def parameters_to_url_query(self, params, collection_formats):
             if k in collection_formats:
                 collection_format = collection_formats[k]
                 if collection_format == 'multi':
-                    new_params.extend((k, quote(str(value))) for value in v)
+                    new_params.extend(
+                        (k, quote(str(value).lower() if isinstance(value, bool) else str(value)))
+                        for value in v
+                    )
                 else:
                     if collection_format == 'ssv':
                         delimiter = ' '
@@ -539,7 +549,9 @@ def parameters_to_url_query(self, params, collection_formats):
                     else:  # csv is the default
                         delimiter = ','
                     new_params.append(
-                        (k, delimiter.join(quote(str(value)) for value in v))
+                        (k, delimiter.join(
+                            quote(str(value).lower() if isinstance(value, bool) else str(value))
+                            for value in v))
                     )
             else:
                 new_params.append((k, quote(str(v))))

From b2e9e746338c7195ed73d94517e919cd8367a536 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=B5=E3=81=81?= <yuki@yuki0311.com>
Date: Mon, 20 Jul 2026 07:29:04 +0000
Subject: [PATCH 3/3] [python] update echo_api header test for lowercase
 boolean

The manual header test asserted the old buggy 'True'; with booleans now
serialized as 'true' the echo server reflects 'true'.
---
 samples/client/echo_api/python/tests/test_manual.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/client/echo_api/python/tests/test_manual.py b/samples/client/echo_api/python/tests/test_manual.py
index 8572845b9ab8..b63f5b36dcb1 100644
--- a/samples/client/echo_api/python/tests/test_manual.py
+++ b/samples/client/echo_api/python/tests/test_manual.py
@@ -61,7 +61,7 @@ def testHeaderParameters(self):
         e = EchoServerResponseParser(api_response)
         expected_header = dict(
             integer_header="123",
-            boolean_header="True",
+            boolean_header="true",
             string_header="string_value",
             enum_nonref_string_header="success",
             enum_ref_string_header="failure",