PEP 238: Changing the Division Operator

2.2

1 // 2 == 0 is explicit floor division.

from __future__ import division enables "true division": 1 / 2 == 0.5.

Standard library already clean for -Qnew mode.

3.0?

True division becomes default.

PEP 237: Unifying Long Integers and Integers

2.2

What used to raise OverflowError (e.g. 2 ** 40), automatically converts to long. 'L' suffix is optional.

2.3

What used to silently lose bits (e.g. 1 << 40), still does but prints FutureWarning.

2.4

No warning, long behavior completely wins.

PEP 285: A Boolean Type

2.2.1 [*]

False, True = 0, 1

2.3

True + True == 2 forever but str(bool(1)) == "True"

PEP 218: A Standard Set Datatype

2.3 (the module works on 2.2 if you copy it)

Python sets module: sets.Set(), sets.ImmutableSet(). Supports boolean algebra operations.

dict.fromkeys(keys, value=None) builds set-like dicts.

2.4

Builtin types implemented in C: set(), frozenset() (same thing except for auto-freezing keys). The sets module remains for compatibility.

2.5

Builtin set(), frozenset() optimized (not internally based on dict now).

Sorting goodies

2.3

list.sort() heavily optimized.

2.4

sorted(iterable) returns new sorted list.

Keyword arguments cmp, key, reverse make common cases easier.

operator.attrgetter() and operator.itemgetter() handy as key functions.

2.5

min() and max() gain key arguments.

operator.attrgetter() and operator.itemgetter() support multiple arguments (return tuples).

PEP 234: Iterators

2.2

New iterable.__iter__() protocol returning an iterator that has iterator.next() until it raises StopIteration. New iter() builtin. for loop now uses this protocol. So do many constructors (e.g. list() and functions (e.g. max).

Iterators for builtin types: files (lines), sequences, dicts (keys).

2.3

itertools module with things like chain, ifilter, izip.

enumarate(["a", "b", "c"]) yields (0, "a"), (1, "b"), (2, "c")

2.4

PEP 322: Reverse Iteration: for i in reversed(sequence).

PEP 323: Copyable Iterators: iterator.__copy__(), itertools.tee().

2.5

Cleanup after iteration: iterator.close(), iterator.throw(exc).

Co-routines: iterator.send(value) instead of iterator.next().

PEP 255: Simple Generators

2.2

yield inside function makes it return a generator object - cool way to implement iterators. Requires from __future__ import generators.

2.3

yield availiable without a __future__ import.

2.4

PEP 289: Generator Expressions: sum(x**2 for x in range(5)).

2.5

yield responds to generator.close() and generator.throw(). Can now yield inside try..finally.

yield is an expression, responds to generator.send(value).

Reduction

2.3

sum() builting added and starts a trend of reduction functions.

2.5

any() and all() boolean reduction functions added.

PEP 318: Decorators for Functions and Methods

2.2

staticmethod(), classmethod() wrappers for methods.

2.4

@decorator before functions.

Note: property() still not handled cleanly, metaclasses still ugly black magic. This is a very open field.

PEP 343: The "with" Statement

2.5 [details still not final]

with statement to abstract enter-exit patterns.

Will have it's own __enter__()/__exit__() protocol but a standard decorator would wrap generators as with context functions.

Conditional expressions

2.2 ~ 2.3

Lots of discussion on syntax, indecisive voting => nothing done.

2.5

THEN if COND else ELSE pronounced by Guido. No fuss.