Remove some blockers for Python3.8 support. (#516)

Remove some blockers for Python3.8 support.

1. Only use pytype on 3.7 since it doesn't work on 3.8+
2. Skip a test that hangs if not on Python3.7.

Also, mark a test as "slow" instead of "long" and register the marker
to avoid getting the warnings.

experiment/build/test_builder.py

@@ -15,6 +15,7 @@
 
 import itertools
 import os
+import sys
 from unittest import mock
 
 import pytest
@@ -62,7 +63,8 @@ def get_benchmarks_or_fuzzers(benchmarks_or_fuzzers_directory, filename,
     ]
 
 
-# This test seems to hang on Python3.8+
+@pytest.mark.skipif(sys.version_info.minor > 7,
+                    reason='Test can hang on versions greater than 3.7')
 @mock.patch('experiment.build.builder.build_measurer')
 @mock.patch('time.sleep')
 @pytest.mark.parametrize('build_measurer_return_value', [True, False])

experiment/test_run_experiment.py

@@ -226,7 +226,7 @@ def test_validate_experiment_name_invalid(experiment_name):
 
 
 # This test takes up to a minute to complete.
-@pytest.mark.long
+@pytest.mark.slow
 def test_copy_resources_to_bucket(tmp_path):
     """Tests that copy_resources_to_bucket copies the correct resources."""
     # Do this so that Ctrl-C doesn't pollute the repo.

presubmit.py

@@ -210,6 +210,15 @@ def lint(paths: List[Path]) -> bool:
 def pytype(paths: List[Path]) -> bool:
     """Run pytype on |path| if it is a python file. Return False if it fails
     type checking."""
+    # Pytype isn't supported on Python3.8+. See
+    # https://github.com/google/pytype/issues/440.
+    assert sys.version_info.major == 3, "Need Python3."
+    if sys.version_info.minor > 7:
+        logs.error(
+            'Python version is: "%s". You should be using 3.7. '
+            'Not running pytype.', sys.version)
+        return True
+
     paths = [path for path in paths if is_python(path)]
     if not paths:
         return True

pytest.ini

@@ -1,2 +1,5 @@
 [pytest]
 norecursedirs = docs/_site/* docs/vendor/* third_party/* .venv/*
+
+markers =
+    slow: marks tests as slow (deselect with '-m "not slow"')