pyflakes silently failing on travis-ci

[pkienzle]

pyflakes 1.1.0 is failing with an internal error AttributeError: 'Checker' object has no attribute 'JOINEDSTR'. Version 2.1.0 runs to completion (though with many warnings, as indicated in #11529).

See also recent travis build results (even ones that pass!), such as
https://travis-ci.org/github/scipy/scipy/jobs/671749102?utm_medium=notification&utm_source=github_status (scroll to line 553).

Reproducing code example:

Follow the steps in .travis.yml on your local development machine:

pip install pyflakes==1.1.0
PYFLAKES_NODOCTEST=1 pyflakes scipy benchmarks/benchmarks

Error message:

...
scipy/linalg/tests/test_decomp.py:2448: local variable '_' is assigned to but never used
scipy/linalg/tests/test_decomp_cossin.py:8: 'block_diag' imported but unused
Traceback (most recent call last):
  File "/Users/pkienzle/conda/envs/bumps/bin/pyflakes", line 8, in <module>
    sys.exit(main())
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/api.py", line 184, in main
    warnings = checkRecursive(args, reporter)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/api.py", line 141, in checkRecursive
    warnings += checkPath(sourcePath, reporter)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/api.py", line 108, in checkPath
    return check(codestr, filename, reporter)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/api.py", line 69, in check
    w = checker.Checker(tree, filename)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 329, in __init__
    self.runDeferred(self._deferredFunctions)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 366, in runDeferred
    handler()
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 958, in runFunction
    self.handleNode(stmt, node)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 697, in handleNode
    handler(node)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 650, in handleChildren
    self.handleNode(node, tree)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 697, in handleNode
    handler(node)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 650, in handleChildren
    self.handleNode(node, tree)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 697, in handleNode
    handler(node)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 650, in handleChildren
    self.handleNode(node, tree)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 697, in handleNode
    handler(node)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 650, in handleChildren
    self.handleNode(node, tree)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 696, in handleNode
    handler = self.getNodeHandler(node.__class__)
  File "/Users/pkienzle/conda/envs/bumps/lib/python3.7/site-packages/pyflakes/checker.py", line 530, in getNodeHandler
    self._nodeHandlers[node_class] = handler = getattr(self, nodeType)
AttributeError: 'Checker' object has no attribute 'JOINEDSTR'

Scipy/Numpy/Python version information:

1.3.1 1.17.3 sys.version_info(major=3, minor=7, micro=3, releaselevel='final', serial=0)