diff --git a/docs/config-file/v2.rst b/docs/config-file/v2.rst
index 2de0411ae94..040a8e57bc1 100644
--- a/docs/config-file/v2.rst
+++ b/docs/config-file/v2.rst
@@ -31,7 +31,7 @@ Below is an example YAML file which shows the most common configuration options:
 
          # Optionally set the version of Python and requirements required to build your docs
          python:
-            version: 3.7
+            version: "3.7"
             install:
             - requirements: docs/requirements.txt
 
@@ -51,7 +51,7 @@ Below is an example YAML file which shows the most common configuration options:
 
          # Optionally set the version of Python and requirements required to build your docs
          python:
-            version: 3.7
+            version: "3.7"
             install:
             - requirements: docs/requirements.txt
 
@@ -138,7 +138,7 @@ Configuration of the Python environment to be used.
    version: 2
 
    python:
-     version: 3.7
+     version: "3.7"
      install:
        - requirements: docs/requirements.txt
        - method: pip
@@ -154,13 +154,18 @@ python.version
 
 The Python version (this depends on :ref:`config-file/v2:build.image`).
 
-:Type: ``number``
+:Type: ``string``
 :Default: ``3``
 
+.. note::
+
+   Make sure to use quotes (``"``) to make it a string.
+   We previously supported using numbers here,
+   but that approach is deprecated.
 .. warning::
 
-  If you are using a :ref:`Conda <config-file/v2:conda>` environment to manage
-  the build, this setting will not have any effect, as the Python version is managed by Conda.
+   If you are using a :ref:`Conda <config-file/v2:conda>` environment to manage
+   the build, this setting will not have any effect, as the Python version is managed by Conda.
 
 python.install
 ``````````````
@@ -189,7 +194,7 @@ Example:
    version: 2
 
    python:
-     version: 3.7
+     version: "3.7"
      install:
        - requirements: docs/requirements.txt
        - requirements: requirements.txt
@@ -237,7 +242,7 @@ Example:
    version: 2
 
    python:
-     version: 3.7
+     version: "3.7"
      install:
        - method: pip
          path: .
@@ -308,7 +313,7 @@ Configuration for the documentation build process.
        - cmake
 
    python:
-     version: 3.7
+     version: "3.7"
 
 
 build.image
diff --git a/readthedocs/config/config.py b/readthedocs/config/config.py
index c1a3c4c8029..0a9f37c2003 100644
--- a/readthedocs/config/config.py
+++ b/readthedocs/config/config.py
@@ -254,23 +254,22 @@ def validate(self):
 
     @property
     def python_interpreter(self):
-        ver = self.python_full_version
-        if not ver or isinstance(ver, (int, float)):
-            return 'python{}'.format(ver)
-
-        # Allow to specify ``pypy3.5`` as Python interpreter
-        return ver
+        version = self.python_full_version
+        if version.startswith('pypy'):
+            # Allow to specify ``pypy3.5`` as Python interpreter
+            return version
+        return f'python{version}'
 
     @property
     def python_full_version(self):
-        ver = self.python.version
-        if ver in [2, 3]:
+        version = self.python.version
+        if version in ['2', '3']:
             # use default Python version if user only set '2', or '3'
             return self.get_default_python_version_for_image(
                 self.build.image,
-                ver,
+                version,
             )
-        return ver
+        return version
 
     @property
     def valid_build_images(self):
@@ -454,7 +453,7 @@ def validate_python(self):
         """Validates the ``python`` key, set default values it's necessary."""
         install_project = self.defaults.get('install_project', False)
         use_system_packages = self.defaults.get('use_system_packages', False)
-        version = self.defaults.get('python_version', 2)
+        version = self.defaults.get('python_version', '2')
         python = {
             'use_system_site_packages': use_system_packages,
             'install_with_pip': False,
@@ -513,17 +512,7 @@ def validate_python(self):
 
             if 'version' in raw_python:
                 with self.catch_validation_error('python.version'):
-                    # Try to convert strings to an int first, to catch '2', then
-                    # a float, to catch '2.7'
-                    version = raw_python['version']
-                    if isinstance(version, str):
-                        try:
-                            version = int(version)
-                        except ValueError:
-                            try:
-                                version = float(version)
-                            except ValueError:
-                                pass
+                    version = str(raw_python['version'])
                     python['version'] = validate_choice(
                         version,
                         self.get_valid_python_versions(),
@@ -839,15 +828,13 @@ def validate_python(self):
 
         python = {}
         with self.catch_validation_error('python.version'):
-            version = self.pop_config('python.version', 3)
-            if isinstance(version, str):
-                try:
-                    version = int(version)
-                except ValueError:
-                    try:
-                        version = float(version)
-                    except ValueError:
-                        pass
+            version = self.pop_config('python.version', '3')
+            if version == 3.1:
+                # Special case for ``python.version: 3.10``,
+                # yaml will transform this to the numeric value of `3.1`.
+                # Save some frustration to users.
+                version = '3.10'
+            version = str(version)
             python['version'] = validate_choice(
                 version,
                 self.get_valid_python_versions(),
diff --git a/readthedocs/config/tests/test_config.py b/readthedocs/config/tests/test_config.py
index c4bbe6dc069..56d832befd6 100644
--- a/readthedocs/config/tests/test_config.py
+++ b/readthedocs/config/tests/test_config.py
@@ -341,18 +341,18 @@ class TestValidatePythonVersion:
     def test_it_defaults_to_a_valid_version(self):
         build = get_build_config({'python': {}})
         build.validate()
-        assert build.python.version == 2
+        assert build.python.version == '2'
         assert build.python_interpreter == 'python2.7'
-        assert build.python_full_version == 2.7
+        assert build.python_full_version == '2.7'
 
     def test_it_supports_other_versions(self):
         build = get_build_config(
             {'python': {'version': 3.7}},
         )
         build.validate()
-        assert build.python.version == 3.7
+        assert build.python.version == '3.7'
         assert build.python_interpreter == 'python3.7'
-        assert build.python_full_version == 3.7
+        assert build.python_full_version == '3.7'
 
     def test_it_supports_string_versions(self):
         build = get_build_config(
@@ -381,28 +381,11 @@ def test_it_validates_wrong_type(self):
         assert excinfo.value.key == 'python.version'
         assert excinfo.value.code == INVALID_CHOICE
 
-    def test_it_validates_wrong_type_right_value(self):
-        build = get_build_config(
-            {'python': {'version': '3.6'}},
-        )
-        build.validate()
-        assert build.python.version == 3.6
-        assert build.python_interpreter == 'python3.6'
-        assert build.python_full_version == 3.6
-
-        build = get_build_config(
-            {'python': {'version': '3'}},
-        )
-        build.validate()
-        assert build.python.version == 3
-        assert build.python_interpreter == 'python3.7'
-        assert build.python_full_version == 3.7
-
     def test_it_validates_env_supported_versions(self):
         build = get_build_config(
-            {'python': {'version': 3.6}},
+            {'python': {'version': '3.6'}},
             env_config={
-                'python': {'supported_versions': [3.5]},
+                'python': {'supported_versions': ['3.5']},
                 'build': {'image': 'custom'},
             },
         )
@@ -412,18 +395,18 @@ def test_it_validates_env_supported_versions(self):
         assert excinfo.value.code == INVALID_CHOICE
 
         build = get_build_config(
-            {'python': {'version': 3.6}},
+            {'python': {'version': '3.6'}},
             env_config={
-                'python': {'supported_versions': [3.5, 3.6]},
+                'python': {'supported_versions': ['3.5', '3.6']},
                 'build': {'image': 'custom'},
             },
         )
         build.validate()
-        assert build.python.version == 3.6
+        assert build.python.version == '3.6'
         assert build.python_interpreter == 'python3.6'
-        assert build.python_full_version == 3.6
+        assert build.python_full_version == '3.6'
 
-    @pytest.mark.parametrize('value', [2, 3])
+    @pytest.mark.parametrize('value', ['2', '3'])
     def test_it_respects_default_value(self, value):
         defaults = {
             'python_version': value,
@@ -741,7 +724,7 @@ def test_as_dict(tmpdir):
         'version': '1',
         'formats': ['pdf'],
         'python': {
-            'version': 3.7,
+            'version': '3.7',
             'install': [{
                 'requirements': 'requirements.txt',
             }],
@@ -1003,8 +986,8 @@ def test_python_check_invalid_types(self, value):
     @pytest.mark.parametrize(
         'image,versions',
         [
-            ('latest', [2, 2.7, 3, 3.5, 3.6, 3.7, 'pypy3.5']),
-            ('stable', [2, 2.7, 3, 3.5, 3.6, 3.7]),
+            ('latest', ['2', '2.7', '3', '3.5', '3.6', '3.7', 'pypy3.5']),
+            ('stable', ['2', '2.7', '3', '3.5', '3.6', '3.7']),
         ],
     )
     def test_python_version(self, image, versions):
@@ -1030,7 +1013,31 @@ def test_python_version_accepts_string(self):
             },
         })
         build.validate()
-        assert build.python.version == 3.6
+        assert build.python.version == '3.6'
+
+    def test_python_version_accepts_number(self):
+        build = self.get_build_config({
+            'build': {
+                'image': 'latest',
+            },
+            'python': {
+                'version': 3.6,
+            },
+        })
+        build.validate()
+        assert build.python.version == '3.6'
+
+    def test_python_version_310_as_number(self):
+        build = self.get_build_config({
+            'build': {
+                'image': 'testing',
+            },
+            'python': {
+                'version': 3.10,
+            },
+        })
+        build.validate()
+        assert build.python.version == '3.10'
 
     @pytest.mark.parametrize(
         'image,versions',
@@ -1056,27 +1063,27 @@ def test_python_version_invalid(self, image, versions):
     def test_python_version_default(self):
         build = self.get_build_config({})
         build.validate()
-        assert build.python.version == 3
+        assert build.python.version == '3'
 
     @pytest.mark.parametrize(
-        'image,default_version',
+        'image, default_version, full_version',
         [
-            ('2.0', 3.5),
-            ('4.0', 3.7),
-            ('5.0', 3.7),
-            ('latest', 3.7),
-            ('stable', 3.7),
+            ('2.0', '3', '3.5'),
+            ('4.0', '3', '3.7'),
+            ('5.0', '3', '3.7'),
+            ('latest', '3', '3.7'),
+            ('stable', '3', '3.7'),
         ],
     )
-    def test_python_version_default_from_image(self, image, default_version):
+    def test_python_version_default_from_image(self, image, default_version, full_version):
         build = self.get_build_config({
             'build': {
                 'image': image,
             },
         })
         build.validate()
-        assert build.python.version == int(default_version)  # 2 or 3
-        assert build.python_full_version == default_version
+        assert build.python.version == default_version
+        assert build.python_full_version == full_version
 
     @pytest.mark.parametrize('value', [2, 3])
     def test_python_version_overrides_default(self, value):
@@ -1085,13 +1092,13 @@ def test_python_version_overrides_default(self, value):
             {'defaults': {'python_version': value}},
         )
         build.validate()
-        assert build.python.version == 3
+        assert build.python.version == '3'
 
-    @pytest.mark.parametrize('value', [2, 3, 3.6])
+    @pytest.mark.parametrize('value', ['2', '3', '3.6'])
     def test_python_version_priority_over_default(self, value):
         build = self.get_build_config(
             {'python': {'version': value}},
-            {'defaults': {'python_version': 3}},
+            {'defaults': {'python_version': '3'}},
         )
         build.validate()
         assert build.python.version == value
@@ -2109,7 +2116,7 @@ def test_as_dict(self, tmpdir):
                 'version': 2,
                 'formats': ['pdf'],
                 'python': {
-                    'version': 3.6,
+                    'version': '3.6',
                     'install': [{
                         'requirements': 'requirements.txt',
                     }],
@@ -2122,7 +2129,7 @@ def test_as_dict(self, tmpdir):
             'version': '2',
             'formats': ['pdf'],
             'python': {
-                'version': 3.6,
+                'version': '3.6',
                 'install': [{
                     'requirements': 'requirements.txt',
                 }],
diff --git a/readthedocs/doc_builder/config.py b/readthedocs/doc_builder/config.py
index 5f57a4402b1..02e7818578d 100644
--- a/readthedocs/doc_builder/config.py
+++ b/readthedocs/doc_builder/config.py
@@ -24,7 +24,7 @@ def load_yaml_config(version):
     # can be rejected at validation
 
     img_name = project.container_image or DOCKER_IMAGE
-    python_version = 3 if project.python_interpreter == 'python3' else 2
+    python_version = '3' if project.python_interpreter == 'python3' else '2'
     try:
         sphinx_configuration = path.join(
             version.get_conf_py_path(),
diff --git a/readthedocs/rtd_tests/tests/test_config_integration.py b/readthedocs/rtd_tests/tests/test_config_integration.py
index acd65232826..f8928be5526 100644
--- a/readthedocs/rtd_tests/tests/test_config_integration.py
+++ b/readthedocs/rtd_tests/tests/test_config_integration.py
@@ -99,7 +99,7 @@ def test_python_supported_versions_default_image_1_0(self, load_config):
                 ],
                 'use_system_packages': self.project.use_system_packages,
                 'requirements_file': self.project.requirements_file,
-                'python_version': 3,
+                'python_version': '3',
                 'sphinx_configuration': mock.ANY,
                 'build_image': 'readthedocs/build:1.0',
                 'doctype': self.project.documentation_type,
@@ -114,7 +114,7 @@ def test_python_supported_versions_default_image_1_0(self, load_config):
                 path=mock.ANY,
                 env_config=expected_env_config,
         )
-        self.assertEqual(config.python.version, 3)
+        self.assertEqual(config.python.version, '3')
 
     @mock.patch('readthedocs.doc_builder.config.load_config')
     def test_python_supported_versions_image_2_0(self, load_config):
@@ -124,7 +124,7 @@ def test_python_supported_versions_image_2_0(self, load_config):
         config = load_yaml_config(self.version)
         self.assertEqual(
             config.get_valid_python_versions(),
-            [2, 2.7, 3, 3.5],
+            ['2', '2.7', '3', '3.5'],
         )
 
     @mock.patch('readthedocs.doc_builder.config.load_config')
@@ -135,14 +135,14 @@ def test_python_supported_versions_image_latest(self, load_config):
         config = load_yaml_config(self.version)
         self.assertEqual(
             config.get_valid_python_versions(),
-            [2, 2.7, 3, 3.5, 3.6, 3.7, 3.8, 'pypy3.5'],
+            ['2', '2.7', '3', '3.5', '3.6', '3.7', '3.8', 'pypy3.5'],
         )
 
     @mock.patch('readthedocs.doc_builder.config.load_config')
     def test_python_default_version(self, load_config):
         load_config.side_effect = create_load()
         config = load_yaml_config(self.version)
-        self.assertEqual(config.python.version, 3)
+        self.assertEqual(config.python.version, '3')
         self.assertEqual(config.python_interpreter, 'python3.7')
 
     @mock.patch('readthedocs.doc_builder.config.load_config')
@@ -152,7 +152,7 @@ def test_python_set_python_version_on_project(self, load_config):
         self.project.python_interpreter = 'python3'
         self.project.save()
         config = load_yaml_config(self.version)
-        self.assertEqual(config.python.version, 3)
+        self.assertEqual(config.python.version, '3')
         self.assertEqual(config.python_interpreter, 'python3.5')
 
     @mock.patch('readthedocs.doc_builder.config.load_config')
@@ -163,9 +163,19 @@ def test_python_set_python_version_in_config(self, load_config):
         self.project.container_image = 'readthedocs/build:2.0'
         self.project.save()
         config = load_yaml_config(self.version)
-        self.assertEqual(config.python.version, 3.5)
+        self.assertEqual(config.python.version, '3.5')
         self.assertEqual(config.python_interpreter, 'python3.5')
 
+    @mock.patch('readthedocs.doc_builder.config.load_config')
+    def test_python_set_python_310_version_in_config(self, load_config):
+        load_config.side_effect = create_load({
+            'build': {'image': 'testing'},
+            'python': {'version': '3.10'},
+        })
+        config = load_yaml_config(self.version)
+        self.assertEqual(config.python.version, '3.10')
+        self.assertEqual(config.python_interpreter, 'python3.10')
+
     @mock.patch('readthedocs.doc_builder.config.load_config')
     def test_python_invalid_version_in_config(self, load_config):
         load_config.side_effect = create_load({
@@ -523,8 +533,8 @@ def test_python_version(self, checkout_path, tmpdir):
         self.project.save()
 
         config = self.get_update_docs_task().config
-        assert config.python.version == 3
-        assert config.python_full_version == 3.7
+        assert config.python.version == '3'
+        assert config.python_full_version == '3.7'
 
     @patch('readthedocs.doc_builder.environments.BuildEnvironment.run')
     def test_python_install_requirements(self, run, checkout_path, tmpdir):
diff --git a/readthedocs/rtd_tests/tests/test_doc_building.py b/readthedocs/rtd_tests/tests/test_doc_building.py
index 82cfa210a76..f0b8599ad6c 100644
--- a/readthedocs/rtd_tests/tests/test_doc_building.py
+++ b/readthedocs/rtd_tests/tests/test_doc_building.py
@@ -1501,7 +1501,7 @@ def test_save_environment_json(self, load_config):
                 'hash': 'a1b2c3',
             },
             'python': {
-                'version': 2.7,
+                'version': '2.7',
             },
             'env_vars_hash': env_vars_hash
         }
@@ -1638,7 +1638,7 @@ def test_is_obsolete_with_json_same_data_as_version(self, load_config):
         m.update(env_var_str.encode('utf-8'))
         env_vars_hash = m.hexdigest()
 
-        env_json_data = '{{"build": {{"image": "readthedocs/build:2.0", "hash": "a1b2c3"}}, "python": {{"version": 3.5}}, "env_vars_hash": "{}"}}'.format(env_vars_hash)  # noqa
+        env_json_data = '{{"build": {{"image": "readthedocs/build:2.0", "hash": "a1b2c3"}}, "python": {{"version": "3.5"}}, "env_vars_hash": "{}"}}'.format(env_vars_hash)  # noqa
         with patch('os.path.exists') as exists, patch('readthedocs.doc_builder.python_environments.open', mock_open(read_data=env_json_data)) as _open:  # noqa
             exists.return_value = True
             self.assertFalse(python_env.is_obsolete)
diff --git a/readthedocs/settings/base.py b/readthedocs/settings/base.py
index 4b76c941c5a..e30011cecb2 100644
--- a/readthedocs/settings/base.py
+++ b/readthedocs/settings/base.py
@@ -455,50 +455,51 @@ def TEMPLATES(self):
         # We must have documented it at some point.
         'readthedocs/build:2.0': {
             'python': {
-                'supported_versions': [2, 2.7, 3, 3.5],
+                'supported_versions': ['2', '2.7', '3', '3.5'],
                 'default_version': {
-                    2: 2.7,
-                    3: 3.5,
+                    '2': '2.7',
+                    '3': '3.5',
                 },
             },
         },
         'readthedocs/build:4.0': {
             'python': {
-                'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7],
+                'supported_versions': ['2', '2.7', '3', '3.5', '3.6', 3.7],
                 'default_version': {
-                    2: 2.7,
-                    3: 3.7,
+                    '2': '2.7',
+                    '3': '3.7',
                 },
             },
         },
         'readthedocs/build:5.0': {
             'python': {
-                'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7, 'pypy3.5'],
+                'supported_versions': ['2', '2.7', '3', '3.5', '3.6', '3.7', 'pypy3.5'],
                 'default_version': {
-                    2: 2.7,
-                    3: 3.7,
+                    '2': '2.7',
+                    '3': '3.7',
                 },
             },
         },
         'readthedocs/build:6.0': {
             'python': {
-                'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7, 3.8, 'pypy3.5'],
+                'supported_versions': ['2', '2.7', '3', '3.5', '3.6', '3.7', '3.8', 'pypy3.5'],
                 'default_version': {
-                    2: 2.7,
-                    3: 3.7,
+                    '2': '2.7',
+                    '3': '3.7',
                 },
             },
         },
         'readthedocs/build:7.0': {
             'python': {
-                'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7, 3.8, 3.9, 'pypy3.5'],
+                'supported_versions': ['2', '2.7', '3', '3.5', '3.6', '3.7', '3.8', '3.9', '3.10', 'pypy3.5'],
                 'default_version': {
-                    2: 2.7,
-                    3: 3.7,
+                    '2': '2.7',
+                    '3': '3.7',
                 },
             },
         },
     }
+
     # Alias tagged via ``docker tag`` on the build servers
     DOCKER_IMAGE_SETTINGS.update({
         'readthedocs/build:stable': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:5.0'),