Python 3: ten years later

Draft of the talk:

• Growing populary of the Python programming language

  • Defacto language in the scientific world, replacing other closed source and more specialized but limited language
  • Favorite programming language used as the first language to learn programming

• Port Python 2 code to Python 3

  • Port Python 2 code to Python 3

  • No: “Add support for Python 3”, don’t loose Python 2 support

  • Port Python 3 code to Python 2

  • Python changes to make the transition smoother:

  • PEP 414: u"syntax” reintroduced in Python 3.3

  • PEP 461: bytes % args, Python 3.5
  • More “Py3k” warnings added to Python 2.7.x
  • Linters like flake8 detect some issues
  • six, futures, modernize, 2to6, etc.

• Analysis of the transition

  • Good: At Pycon US 2014, Guido van Rossum announced that the Python 2.7 support was extended from 2015 to 2020 to give more time to companies to port their applications to Python 3.
  • Bad: 2to3: “drop Python2 support at once”, don’t work when you have dependencies.
  • If done again, would it be different? Yes, obviously.
  • Python 4 will be different than Python 3: no more “break the world” release, but a “regular deprecation period” release, as any other release. Break things, one by one :-)

• Bugs that won’t be fixed in Python 2 anymore

  • Some bugs cannot be fixed without breaking the backward compatibility
  • Unicode Support
  • Python 2 I/O stack bugs: rely on libc stdio.h
  • Security: hash DoS, enabled by default in Python 3.3, Python 3.4 now uses SipHash
  • subprocess is not thread-safe in Python 2. Python 2 subprocess has many race conditions: fixed in Python 3 with a C implementation which has less or no race condition. Handling signals while forking in complex.
  • threading.RLock is not “signal safe” in Python 2
  • Python 2 requires polling to wait for a lock or for I/O. Python 3 uses native threading API with timeout and has asyncio.
  • Python 3 uses a monotonic clock to not crash on system clock update (ex: DST change).
  • Python 3 has a better GIL.
  • Python 2 inherits file descriptors on fork+exec by default. Python 3 don’t: PEP 446.
  • Functions can fail with OSError(EINTR) when interrupted by a signal, need to be very careful everywhere. SIGCHLD when a child process completes, SIGWINCH when using ncurses. Python 3.5 restarts the interrupted system call for you.

• Performance

  • Python 3.6 is now faster than Python 2.7
  • https://speed.python.org/

• Evolutions of the Python language

  • Python 3.5

  • PEP 492: async/await “keywords” for asyncio. (Really keywords in Python 3.7.)

  • PEP 461: bytes % args and bytearray % args
  • PEP 465, a new matrix multiplication operator: a @ b.

  • PEP 448: Generalized unpacking: head, *tail = list mylist = [1, 2, **other_list] mydict = {"key": "value", **other_dict}

  • Python 3.6

  • PEP 515: million = 1_000_000

  • PEP 498: f-string: name = "World"; print(f"Hello {name}!")
  • PEP 526, syntax for variable annotations.
  • PEP 525, asynchronous generators.
  • PEP 530: asynchronous comprehensions.

• Bury Python 2?

  • “Python 3 only”
  • https://pythonclock.org/
  • http://www.python3statement.org/
  • Fedora 23, Ubuntu 17.10: no python2 (/usr/bin/python) in the base system
  • 2017, April: IPython 6.0
  • 2017, December: Django 2