Use pip-tools to deal with Python dependencies

requirements-dev.in

+black
+flake8
+pip-tools

requirements-dev.txt

+#
+# This file is autogenerated by pip-compile with python 3.9
+# To update, run:
+#
+#    pip-compile requirements-dev.in
+#
+black==21.12b0
+    # via -r requirements-dev.in
+click==8.0.3
+    # via
+    #   black
+    #   pip-tools
+flake8==4.0.1
+    # via -r requirements-dev.in
+mccabe==0.6.1
+    # via flake8
+mypy-extensions==0.4.3
+    # via black
+pathspec==0.9.0
+    # via black
+pep517==0.12.0
+    # via pip-tools
+pip-tools==6.4.0
+    # via -r requirements-dev.in
+platformdirs==2.4.1
+    # via black
+pycodestyle==2.8.0
+    # via flake8
+pyflakes==2.4.0
+    # via flake8
+tomli==1.2.3
+    # via
+    #   black
+    #   pep517
+typing-extensions==4.0.1
+    # via black
+wheel==0.37.1
+    # via pip-tools
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip
+# setuptools

requirements.in

+Jinja2
+Pillow
+pyyaml
+python-ulid

requirements.txt

-Jinja2
-Pillow
-pyyaml
-python-dotenv
+#
+# This file is autogenerated by pip-compile with python 3.9
+# To update, run:
+#
+#    pip-compile requirements.in
+#
+jinja2==3.0.3
+    # via -r requirements.in
+markupsafe==2.0.1
+    # via jinja2
+pillow==9.0.0
+    # via -r requirements.in
+python-ulid==1.0.3
+    # via -r requirements.in
+pyyaml==6.0
+    # via -r requirements.in