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The first example was extracted from Lib/importlib/_bootstrap.py. The code was maybe wrong, I don't know.
Another example:
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import errno
import os
try:
 os.rmdir("testdir")
except:
 pass
os.mkdir("testdir")
try:
 try:
 #os.mkdir("testdir")
 open("NOT EXISTING FILENAME")
 except OSError as exc:
 if exc.errno == errno.EEXIST:
 pass
 else:
 raise
 except IOError as exc:
 if exc.errno == errno.ENOENT:
 pass
 else:
 raise
except Exception:
 raise
 print("PEP 3151 broke backward compatibility on such pattern!")
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Uncomment mkdir() to test both paths.