Pytest version for Python 2.6.6 - pytest

Question

I am trying to set up pytest on Python 2.6.6 RHEL 6.10.
As pointed out in official change log pytest 3.3.0 doesn't support python 2.6 and hence pytest < 3.3 should be considered. I could successfully install the pytest=3.2.5, but when I execute a simple test I get the following error :
Traceback (most recent call last):
File "/usr/lib64/python2.6/runpy.py", line 122, in _run_module_as_main
"__main__", fname, loader, pkg_name)
File "/usr/lib64/python2.6/runpy.py", line 34, in _run_code
exec code in run_globals
File "/usr/lib/python2.6/site-packages/pytest.py", line 17, in <module>
raise SystemExit(pytest.main())
File "/usr/lib/python2.6/site-packages/_pytest/config.py", line 57, in main
return config.hook.pytest_cmdline_main(config=config)
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 745, in __call__
return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 339, in _hookexec
return self._inner_hookexec(hook, methods, kwargs)
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 334, in <lambda>
_MultiCall(methods, kwargs, hook.spec_opts).execute()
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 614, in execute
res = hook_impl.function(*args)
File "/usr/lib/python2.6/site-packages/_pytest/main.py", line 127, in pytest_cmdline_main
return wrap_session(config, _main)
File "/usr/lib/python2.6/site-packages/_pytest/main.py", line 111, in wrap_session
config.notify_exception(excinfo, config.option)
File "/usr/lib/python2.6/site-packages/_pytest/config.py", line 936, in notify_exception
excinfo=excinfo)
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 745, in __call__
return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 339, in _hookexec
return self._inner_hookexec(hook, methods, kwargs)
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 334, in <lambda>
_MultiCall(methods, kwargs, hook.spec_opts).execute()
File "/usr/lib/python2.6/site-packages/_pytest/vendored_packages/pluggy.py", line 614, in execute
res = hook_impl.function(*args)
File "/usr/lib/python2.6/site-packages/_pytest/terminal.py", line 163, in pytest_internalerror
for line in py.builtin.text(excrepr).split("\n"):
File "/usr/lib/python2.6/site-packages/_pytest/_code/code.py", line 664, in __unicode__
self.toterminal(tw)
File "/usr/lib/python2.6/site-packages/_pytest/_code/code.py", line 709, in toterminal
self.reprtraceback.toterminal(tw)
File "/usr/lib/python2.6/site-packages/_pytest/_code/code.py", line 725, in toterminal
entry.toterminal(tw)
File "/usr/lib/python2.6/site-packages/_pytest/_code/code.py", line 748, in toterminal
tw.write("".join(self.lines))
File "/usr/lib/python2.6/site-packages/py/_io/terminalwriter.py", line 250, in write
self._update_chars_on_current_line(msg)
File "/usr/lib/python2.6/site-packages/py/_io/terminalwriter.py", line 262, in _update_chars_on_current_line
current_line = current_line.decode('utf-8', errors='replace')
TypeError: decode() takes no keyword arguments
A quick search suggested that decode() takes argument in python 2.7.
If this is the case of dependence then which version of pytest is recommended for Python 2.6.6 ?

Answer 1

pytest==3.2.5 is the version that still supports Python 2.6, however just because pytest==3.2.5 supports Python 2.6, does not necessarily mean that its dependencies as the library authors specified in their setup.py supports Python 2.6.
Most packages specifies their dependencies using greater-than constraint, e.g. libxxx>=1.2.3, to ensure you'll automatically get newer versions of dependencies when the depended libraries author released them but you'll never download an incompatible older version. In most cases, this is great as it reduces the workload for the library's authors, but this means that if that depended library released a newer version that drops support for a particular version that the dependant library still supports, you'll be pulling that in, as there's no less-than constraint to prevent that.
In this case, according to the traceback you've shown, the py.io library that got pulled doesn't support python 2.6. You'll need to downgrade and pin py.io to an older version that still supports 2.6.
According to py.io changelog, the last version that still supports Python 2.6 is py.io==1.4.34.
If it's important for you to support an old software, you should create a requirements.txt file to freeze the list of dependencies rather than relying on the automatic version resolution from the packages.