$ echo 24 | python3.8 -m pyflakes
Traceback (most recent call last):
  File ".../lib/python3.8/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File ".../lib/python3.8/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File ".../lib/python3.8/site-packages/pyflakes/__main__.py", line 5, in <module>
    main(prog='pyflakes')
  File ".../lib/python3.8/site-packages/pyflakes/api.py", line 203, in main
    warnings = check(sys.stdin.read(), '<stdin>', reporter)
  File ".../lib/python3.8/site-packages/pyflakes/api.py", line 73, in check
    w = checker.Checker(tree, filename)
  File ".../lib/python3.8/site-packages/pyflakes/checker.py", line 533, in __init__
    self.handleChildren(tree)
  File ".../lib/python3.8/site-packages/pyflakes/checker.py", line 881, in handleChildren
    self.handleNode(node, tree)
  File ".../lib/python3.8/site-packages/pyflakes/checker.py", line 928, in handleNode
    handler(node)
  File ".../lib/python3.8/site-packages/pyflakes/checker.py", line 881, in handleChildren
    self.handleNode(node, tree)
  File ".../lib/python3.8/site-packages/pyflakes/checker.py", line 927, in handleNode
    handler = self.getNodeHandler(node.__class__)
  File ".../lib/python3.8/site-packages/pyflakes/checker.py", line 749, in getNodeHandler
    self._nodeHandlers[node_class] = handler = getattr(self, nodeType)
AttributeError: 'Checker' object has no attribute 'CONSTANT'