Drop Python 3.7 support

Dropping `3.7` as announced here:
https://github.blog/changelog/2023-08-02-deprecation-notice-dependabot-to-drop-support-for-python-3-6-and-3-7/

python/Dockerfile

@@ -4,15 +4,13 @@ ARG PY_3_11=3.11.4
 ARG PY_3_10=3.10.12
 ARG PY_3_9=3.9.17
 ARG PY_3_8=3.8.17
-ARG PY_3_7=3.7.17
 ARG PYENV_VERSION=v2.3.19
 
 FROM ghcr.io/dependabot/dependabot-updater-core as python-core
 ARG PY_3_11
 ARG PY_3_10
 ARG PY_3_9
 ARG PY_3_8
-ARG PY_3_7
 ARG PYENV_VERSION
 USER root
 
@@ -74,13 +72,6 @@ RUN pyenv install $PY_3_8 \
   && cd /usr/local/.pyenv \
   && tar czf 3.8.tar.gz versions/$PY_3_8
 
-FROM python-core as python-3.7
-RUN pyenv install $PY_3_7 \
-  && bash /opt/python/helpers/build $PY_3_7 \
-  && cd /usr/local/.pyenv \
-  && tar czf 3.7.tar.gz versions/$PY_3_7
-
-
 FROM ghcr.io/dependabot/dependabot-updater-core
 ARG PY_3_11
 ARG PYENV_VERSION
@@ -132,7 +123,6 @@ RUN pyenv install $PY_3_11 \
 COPY --from=python-3.10 /usr/local/.pyenv/3.10.tar.gz /usr/local/.pyenv/3.10.tar.gz
 COPY --from=python-3.9 /usr/local/.pyenv/3.9.tar.gz /usr/local/.pyenv/3.9.tar.gz
 COPY --from=python-3.8 /usr/local/.pyenv/3.8.tar.gz /usr/local/.pyenv/3.8.tar.gz
-COPY --from=python-3.7 /usr/local/.pyenv/3.7.tar.gz /usr/local/.pyenv/3.7.tar.gz
 
 COPY --chown=dependabot:dependabot python $DEPENDABOT_HOME/python
 COPY --chown=dependabot:dependabot common $DEPENDABOT_HOME/common

python/lib/dependabot/python/language_version_manager.rb

@@ -12,7 +12,6 @@ class LanguageVersionManager
         3.10.12
         3.9.17
         3.8.17
-        3.7.17
       ).freeze
 
       def initialize(python_requirement_parser:)

python/lib/dependabot/python/update_checker/pip_compile_version_resolver.rb

@@ -235,10 +235,6 @@ def run_command(command, env: python_env, fingerprint:)
           )
         end
 
-        def new_resolver_supported?
-          language_version_manager.python_version >= Python::Version.new("3.7")
-        end
-
         def pip_compile_options_fingerprint(options)
           options.sub(
             /--output-file=\S+/, "--output-file=<output_file>"
@@ -252,8 +248,12 @@ def pip_compile_options_fingerprint(options)
         def pip_compile_options(filename)
           options = @build_isolation ? ["--build-isolation"] : ["--no-build-isolation"]
           options += pip_compile_index_options
+          # TODO: Stop explicitly specifying `allow-unsafe` once it becomes the default:
+          # https://github.com/jazzband/pip-tools/issues/989#issuecomment-1661254701
           options += ["--allow-unsafe"]
-          options += ["--resolver backtracking"] if new_resolver_supported?
+          # TODO: This is the default as of https://github.com/jazzband/pip-tools/releases/tag/7.0.0
+          # so stop explicitly specifying it as soon as we upgrade
+          options += ["--resolver backtracking"]
 
           if (requirements_file = compiled_file_for_filename(filename))
             options << "--output-file=#{requirements_file.name}"

python/spec/dependabot/python/update_checker/pip_version_resolver_spec.rb

@@ -44,7 +44,7 @@
       content: python_version_content
     )
   end
-  let(:python_version_content) { "3.7.0\n" }
+  let(:python_version_content) { "3.11.0\n" }
   let(:pypi_response) { fixture("pypi", "pypi_simple_response_django.html") }
   let(:pypi_url) { "https://pypi.org/simple/django/" }
   let(:dependency) do
@@ -81,16 +81,16 @@
       it { is_expected.to eq(Gem::Version.new("3.2.4")) }
 
       context "that is set to the oldest version of python supported by Dependabot" do
-        let(:python_version_content) { "3.7.0\n" }
+        let(:python_version_content) { "3.8.0\n" }
         it { is_expected.to eq(Gem::Version.new("3.2.4")) }
       end
 
       context "that is set to a python version no longer supported by Dependabot" do
-        let(:python_version_content) { "3.6.0\n" }
+        let(:python_version_content) { "3.7.0\n" }
         it "raises a helpful error" do
           expect { subject }.to raise_error(Dependabot::DependencyFileNotResolvable) do |err|
             expect(err.message).to start_with(
-              "Dependabot detected the following Python requirement for your project: '3.6.0'."
+              "Dependabot detected the following Python requirement for your project: '3.7.0'."
             )
           end
         end
@@ -126,17 +126,17 @@
       it { is_expected.to eq(Gem::Version.new("2.1.1")) }
 
       context "that is set to the oldest version of python supported by Dependabot" do
-        let(:python_version_content) { "3.7.0\n" }
+        let(:python_version_content) { "3.8.0\n" }
         it { is_expected.to eq(Gem::Version.new("2.1.1")) }
       end
 
       context "that is set to a python version no longer supported by Dependabot" do
-        let(:python_version_content) { "3.6.0\n" }
+        let(:python_version_content) { "3.7.0\n" }
 
         it "raises a helpful error" do
           expect { subject }.to raise_error(Dependabot::DependencyFileNotResolvable) do |err|
             expect(err.message).to start_with(
-              "Dependabot detected the following Python requirement for your project: '3.6.0'."
+              "Dependabot detected the following Python requirement for your project: '3.7.0'."
             )
           end
         end

python/spec/dependabot/python/update_checker_spec.rb

@@ -200,7 +200,7 @@
             content: python_version_content
           )
         end
-        let(:python_version_content) { "3.7.0\n" }
+        let(:python_version_content) { "3.11.0\n" }
         let(:pypi_response) do
           fixture("pypi", "pypi_simple_response_django.html")
         end
@@ -219,16 +219,16 @@
         it { is_expected.to eq(Gem::Version.new("3.2.4")) }
 
         context "that is set to the oldest version of python supported by Dependabot" do
-          let(:python_version_content) { "3.7.0\n" }
+          let(:python_version_content) { "3.8.0\n" }
           it { is_expected.to eq(Gem::Version.new("3.2.4")) }
         end
 
         context "that is set to a python version no longer supported by Dependabot" do
-          let(:python_version_content) { "3.6.0\n" }
+          let(:python_version_content) { "3.7.0\n" }
           it "raises a helpful error" do
             expect { subject }.to raise_error(Dependabot::DependencyFileNotResolvable) do |err|
               expect(err.message).to start_with(
-                "Dependabot detected the following Python requirement for your project: '3.6.0'."
+                "Dependabot detected the following Python requirement for your project: '3.7.0'."
               )
             end
           end