diff --git a/__snapshots__/python.js b/__snapshots__/python.js
index 407990e90..8c7ab02f9 100644
--- a/__snapshots__/python.js
+++ b/__snapshots__/python.js
@@ -24,7 +24,7 @@ exports['Python run creates a release PR 1'] = `
   [
     "src/version.py",
     {
-      "content": "# Copyright 2020 Google LLC\\n#\\n# Licensed under the Apache License, Version 2.0 (the \\"License\\");\\n# you may not use this file except in compliance with the License.\\n# You may obtain a copy of the License at\\n#\\n#     https://www.apache.org/licenses/LICENSE-2.0\\n#\\n# Unless required by applicable law or agreed to in writing, software\\n# distributed under the License is distributed on an \\"AS IS\\" BASIS,\\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\\n# See the License for the specific language governing permissions and\\n# limitations under the License.\\n\\n__version__ = \\"0.123.5\\"\\n",
+      "content": "# Copyright 2020 Google LLC\\n#\\n# Licensed under the Apache License, Version 2.0 (the \\"License\\");\\n# you may not use this file except in compliance with the License.\\n# You may obtain a copy of the License at\\n#\\n#     https://www.apache.org/licenses/LICENSE-2.0\\n#\\n# Unless required by applicable law or agreed to in writing, software\\n# distributed under the License is distributed on an \\"AS IS\\" BASIS,\\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\\n# See the License for the specific language governing permissions and\\n# limitations under the License.\\n\\n__version__ = '0.123.5'\\n",
       "mode": "100644"
     }
   ]
@@ -57,7 +57,7 @@ exports['Python run creates a release PR relative to a path 1'] = `
   [
     "projects/python/src/version.py",
     {
-      "content": "# Copyright 2020 Google LLC\\n#\\n# Licensed under the Apache License, Version 2.0 (the \\"License\\");\\n# you may not use this file except in compliance with the License.\\n# You may obtain a copy of the License at\\n#\\n#     https://www.apache.org/licenses/LICENSE-2.0\\n#\\n# Unless required by applicable law or agreed to in writing, software\\n# distributed under the License is distributed on an \\"AS IS\\" BASIS,\\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\\n# See the License for the specific language governing permissions and\\n# limitations under the License.\\n\\n__version__ = \\"0.123.5\\"\\n",
+      "content": "# Copyright 2020 Google LLC\\n#\\n# Licensed under the Apache License, Version 2.0 (the \\"License\\");\\n# you may not use this file except in compliance with the License.\\n# You may obtain a copy of the License at\\n#\\n#     https://www.apache.org/licenses/LICENSE-2.0\\n#\\n# Unless required by applicable law or agreed to in writing, software\\n# distributed under the License is distributed on an \\"AS IS\\" BASIS,\\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\\n# See the License for the specific language governing permissions and\\n# limitations under the License.\\n\\n__version__ = '0.123.5'\\n",
       "mode": "100644"
     }
   ]
diff --git a/__snapshots__/version-py.js b/__snapshots__/version-py.js
index ab2a1ff94..d7da84305 100644
--- a/__snapshots__/version-py.js
+++ b/__snapshots__/version-py.js
@@ -13,6 +13,6 @@ exports['version.py updateContent updates version in version.py 1'] = `
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "0.6.0"
+__version__ = '0.6.0'
 
 `
diff --git a/src/updaters/python/setup-cfg.ts b/src/updaters/python/setup-cfg.ts
index b2b1d2adb..bb1f2f823 100644
--- a/src/updaters/python/setup-cfg.ts
+++ b/src/updaters/python/setup-cfg.ts
@@ -33,8 +33,8 @@ export class SetupCfg implements Update {
   }
   updateContent(content: string): string {
     return content.replace(
-      /version ?= ?[0-9]+\.[0-9]+\.[0-9](-\w+)?/,
-      `version = ${this.version}`
+      /(version ?= ?)[0-9]+\.[0-9]+\.[0-9](?:-\w+)?/,
+      `$1${this.version}`
     );
   }
 }
diff --git a/src/updaters/python/setup-py.ts b/src/updaters/python/setup-py.ts
index fb9c0b7c8..bd7fff06f 100644
--- a/src/updaters/python/setup-py.ts
+++ b/src/updaters/python/setup-py.ts
@@ -33,8 +33,8 @@ export class SetupPy implements Update {
   }
   updateContent(content: string): string {
     return content.replace(
-      /version ?= ?["'][0-9]+\.[0-9]+\.[0-9](-\w+)?["']/,
-      `version = "${this.version}"`
+      /(version ?= ?["'])[0-9]+\.[0-9]+\.[0-9](?:-\w+)?(["'])/,
+      `$1${this.version}$2`
     );
   }
 }
diff --git a/src/updaters/python/version-py.ts b/src/updaters/python/version-py.ts
index 0e84f017f..ec450623f 100644
--- a/src/updaters/python/version-py.ts
+++ b/src/updaters/python/version-py.ts
@@ -33,8 +33,8 @@ export class VersionPy implements Update {
   }
   updateContent(content: string): string {
     return content.replace(
-      /__version__ ?= ?["'][0-9]+\.[0-9]+\.[0-9](-\w+)?["']/,
-      `__version__ = "${this.version}"`
+      /(__version__ ?= ?["'])[0-9]+\.[0-9]+\.[0-9](?:-\w+)?(["'])/,
+      `$1${this.version}$2`
     );
   }
 }
diff --git a/test/updaters/fixtures/version.py b/test/updaters/fixtures/version.py
index 39b40ade4..b6caa68e7 100644
--- a/test/updaters/fixtures/version.py
+++ b/test/updaters/fixtures/version.py
@@ -12,4 +12,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "0.5.0"
+__version__ = '0.5.0'