def has_pyfs():
"""
Does this environment have pyfs installed?
Should return False even when Mercurial's Demand Import allowed import of
fs.*.
"""
with errors.ExceptionRaisedContext() as exc:
fs.__name__
return not bool(exc)
def has_keyczar():
with errors.ExceptionRaisedContext() as exc:
keyczar.__name__
return not bool(exc)
def viable(cls):
with errors.ExceptionRaisedContext() as exc:
cls.priority
return not bool(exc)