https://docs.python.org/3/whatsnew/3.4.html

• PEP 453: Pip should always be available
• PEP 446: Newly created file descriptors are non-inheritable
• PEP 451: A ModuleSpec Type for the Import System

• Unicode database updated to UCD version 6.3.
• min() and max() now accept a default keyword-only argument that can be used to specify the value they return if the iterable they are evaluating has no elements.
• Module objects are now weakref’able.
• Module __file__ attributes (and related values) should now always contain absolute paths by default, with the sole exception of __main__.__file__ when a script has been executed directly using a relative path.
• All the UTF-* codecs (except UTF-7) now reject surrogates during both encoding and decoding unless the surrogatepass error handler is used, with the exception of the UTF-16 decoder and the UTF-16 encoder
• New German EBCDIC codec cp273.
• New Ukrainian codec cp1125.
• bytes.join() and bytearray.join() now accept arbitrary buffer objects as arguments.
• The int constructor now accepts any object that has an __index__ method for its base argument.
• Frame objects now have a clear() method that clears all references to local variables from the frame.
• memoryview is now registered as a Sequence, and supports the reversed() builtin.
• Signatures reported by help() have been modified and improved in several cases as a result of the introduction of Argument Clinic and other changes to the inspect and pydoc modules.
• __length_hint__() is now part of the formal language specification

• asyncio
• ensurepip
• enum
• pathlib
• selectors
• statistics
• tracemalloc

• abc
• aifc
• argparse
• audioop
• base64
• collections
• colorsys
• contextlib
• dbm
• dis
• doctest
• email
• filecmp
• functools
• gc
• glob
• hashlib
• hmac
• html
• http
• idlelib-and-idle
• importlib
• inspect
• ipaddress
• logging
• marshal
• mmap
• multiprocessing
• operator
• os
• pdb
• pickle
• plistlib
• poplib
• pprint
• pty
• pydoc
• re
• resource
• select
• shelve
• shutil
• smtpd
• smtplib
• socket
• sqlite3
• ssl
• stat
• struct
• subprocess
• sunau
• sys
• tarfile
• textwrap
• threading
• traceback
• types
• urllib
• unittest
• venv
• wave
• weakref
• xml-etree

• The PyThreadState.tick_counter field has been removed; its value has been meaningless since Python 3.2, when the “new GIL” was introduced
• PyLoader and PyPycLoader have been removed from importlib.
• The strict argument to HTTPConnection and HTTPSConnection has been removed. HTTP 0.9-style “Simple Responses” are no longer supported.
• The deprecated urllib.request.Request getter and setter methods add_data, has_data, get_data, get_type, get_host, get_selector, set_proxy, get_origin_req_host, and is_unverifiable have been removed (use direct attribute access instead).
• Support for loading the deprecated TYPE_INT64 has been removed from marshal.
• inspect.Signature: positional-only parameters are now required to have a valid name.
• object.__format__() no longer accepts non-empty format strings, it now raises a TypeError instead. Using a non-empty string has been deprecated since Python 3.2
• difflib.SequenceMatcher.isbjunk() and difflib.SequenceMatcher.isbpopular() were deprecated in 3.2, and have now been removed: use x in sm.bjunk and x in sm.bpopular, where sm is a SequenceMatcher object