Python 2.x 3.x compatibility notes

Exceptions

Exception hierachy

Python <= 3.2

• BaseException
  • Exception
    • StandardError
      • EnvironmentError
        • IOError
          • socket.error
        • OSError
    • select.error

Python >= 3.3

• BaseException
  • Exception
    • OSError
      • BlockingIOError
      • EnvironmentError
      • IOError
      • select.error
      • socket.error

Refs

• https://docs.python.org/2/library/exceptions.html#exception-hierarchy
• https://docs.python.org/3/library/exceptions.html#exception-hierarchy
• https://docs.python.org/3/whatsnew/3.3.html#pep-3151

InterruptedError

Python 3.5+ automatically retries system calls that return EINTR.

• https://docs.python.org/3/library/exceptions.html#InterruptedError
• https://docs.python.org/3/whatsnew/3.5.html#pep-475-retry-system-calls-failing-with-eintr

Backports

• https://github.com/PythonBackports?tab=repositories

Files

• open(), os.fdopen(), etc return
  • file instances in Python 2.x
  • io.* instances in Python 3.x
• io module requires Python >= 2.6
• BlockingIOError requires Python >= 3.3 (first doc mention Python 3.4)

Non-blocking behaviour

In non-blocking mode, if n > 0 is specified, and no bytes are available

• io.RawIOBase.read(n) returns None
• io.BufferedIOBase.read(n) is allowed to return None or raise BlockingIOError. io code returns None
• io.BufferedReader.read(n) is the same as io.BufferedIOBase.read(n)

subprocess

• Python >= 2.4
• Python >= 2.6: Popen.send_signal(s), Popen.terminate(), Popen.kill()
• Python >= 3.3: Popen.communicate(..., timeout)