Update requirements

pyproject.toml

@@ -2,6 +2,6 @@
 # Minimum requirements for the build system to execute.
 # PEP 508 specifications for PEP 518.
 requires = [
-    "setuptools > 20.2 ",
+    "setuptools >= 21.0.0,!=24.0.0,!=34.0.0,!=34.0.1,!=34.0.2,!=34.0.3,!=34.1.0,!=34.1.1,!=34.2.0,!=34.3.0,!=34.3.1,!=34.3.2,!=36.2.0",  # PSF/ZPL
     "wheel",
 ]

requirements.txt

@@ -1,2 +1,2 @@
-six >=1.9
+six >=1.10.0
 typing >= 3.6 ; python_version < "3.7"

setup.cfg

@@ -1,10 +1,17 @@
 [options]
 zip_safe = False
 packages = find:
+
+# While setuptools cannot deal with pre-installed incompatible versions,
+# setting a lower bound is not harmful - it makes error messages cleaner. DO
+# NOT set an upper bound on setuptools, as that will lead to uninstallable
+# situations as progressive releases of projects are done.
+# Blacklist setuptools 34.0.0-34.3.2 due to https://github.com/pypa/setuptools/issues/951
+# Blacklist setuptools 36.2.0 due to https://github.com/pypa/setuptools/issues/1086
 setup_requires =
-    setuptools > 20.2
+    setuptools >= 21.0.0,!=24.0.0,!=34.0.0,!=34.0.1,!=34.0.2,!=34.0.3,!=34.1.0,!=34.1.1,!=34.2.0,!=34.3.0,!=34.3.1,!=34.3.2,!=36.2.0
 
-python_requires = >=2.6,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*
+python_requires = >=2.7.5,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*
 
 [bdist_wheel]
 # This flag says that the code is written to work on both Python 2 and Python

tox.ini

@@ -114,9 +114,7 @@ deps = bandit
 commands = bandit -r advanced_descriptors
 
 [testenv:dep-graph]
-envdir = {toxworkdir}/dep-graph
 deps =
-    pipenv
-commands =
-    pipenv install -r {toxinidir}/build_requirements.txt --skip-lock
-    pipenv graph
+    .
+    pipdeptree
+commands = pipdeptree