[Python-Dev] PEP 572: Now with 25% less reference implementation!
Guido van Rossum
guido at python.org
Fri Apr 20 10:42:06 EDT 2018
If you want type hints you can use a variable annotation without
initialization before the statement:
data: bytes
while data := stream.read():
print("Got", data)
On Thu, Apr 19, 2018 at 9:45 PM, Dmitry Malinovsky <damalinov at gmail.com>
wrote:
> Hello Chris, and thank you for working on this PEP!
>
> What do you think about using variable type hints with this syntax?
> I tried to search through python-dev and couldn't find a single post
> discussing that question.
> If I missed it somehow, could you please include its conclusions into the
> PEP?
>
> For instance, as I understand now the parser will fail on this snippet:
>
> while data: bytes := stream.read():
> print("Received data:", data)
>
> Do brackets help?
>
> while (data: bytes := stream.read()):
> print("Received data:", data)
>
> IIUC, in 3.7 It is invalid syntax to specify a type hint for a for loop
> item;
> should brackets help? Currently they don't:
>
> Python 3.7.0b3+ (heads/3.7:7dcfd6c, Mar 30 2018, 21:30:34)
> [Clang 9.0.0 (clang-900.0.39.2)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
> >>> for (x: int) in [1,2,3]:
> File "<stdin>", line 1
> for (x: int) in [1,2,3]:
> ^
> SyntaxError: invalid syntax
>
> Thanks,
>
> > On 20 Apr 2018, at 09:10, Chris Angelico <rosuav at gmail.com> wrote:
> >
> > Working on the reference implementation for PEP 572 is turning out to
> > be a massive time sink, both on my personal schedule and on the PEP's
> > discussion. I can't just hold off all discussion on a topic until I
> > figure out whether something is possible or not, because that could
> > take me several days, even a week or more. And considering the massive
> > backlash against the proposal, it seems like a poor use of my time to
> > try to prove that something's impossible, find that I don't know
> > enough about grammar editing to be able to say anything more than
> > "well, I couldn't do it, but someone else might be able to", and then
> > try to resume the discussion with no more certainty than we had
> > before.
> >
> > So here's the PEP again, simplified. I'm fairly sure it's just going
> > to be another on a growing list of rejected PEPs to my name, and I'm
> > done with trying to argue some of these points. Either the rules get
> > simplified, or they don't. Trying to simplify the rules and maintain
> > perfect backward compatibility is just making the rules even more
> > complicated.
> >
> > PEP 572, if accepted, *will* change the behaviour of certain
> > constructs inside comprehensions, mainly due to interactions with
> > class scope that make no sense unless you know how they're implemented
> > internally. The official tutorial pretends that comprehensions are
> > "equivalent to" longhand:
> >
> > https://docs.python.org/3/tutorial/datastructures.html?
> highlight=equivalent#list-comprehensions
> > https://docs.python.org/3/howto/functional.html?highlight=equivalent#
> generator-expressions-and-list-comprehensions
> >
> > and this is an inaccuracy for the sake of simplicity. PEP 572 will
> > make this far more accurate; the only difference is that the
> > comprehension is inside a function. Current semantics are far more
> > bizarre than that.
> >
> > Do you want absolutely 100% backward compatibility? Then reject this
> > PEP. Or better still, keep using Python 3.7, and don't upgrade to 3.8,
> > in case something breaks. Do you want list comprehensions that make
> > better sense? Then accept that some code will need to change, if it
> > tried to use the same name in multiple scopes, or tried to use ancient
> > Python 2 semantics with a yield expression in the outermost iterable.
> >
> > I'm pretty much ready for pronouncement.
> >
> > https://www.python.org/dev/peps/pep-0572/
> >
> > ChrisA
> >
> > PEP: 572
> > Title: Assignment Expressions
> > Author: Chris Angelico <rosuav at gmail.com>
> > Status: Draft
> > Type: Standards Track
> > Content-Type: text/x-rst
> > Created: 28-Feb-2018
> > Python-Version: 3.8
> > Post-History: 28-Feb-2018, 02-Mar-2018, 23-Mar-2018, 04-Apr-2018,
> 17-Apr-2018
> >
> >
> > Abstract
> > ========
> >
> > This is a proposal for creating a way to assign to variables within an
> > expression. Additionally, the precise scope of comprehensions is
> adjusted, to
> > maintain consistency and follow expectations.
> >
> >
> > Rationale
> > =========
> >
> > Naming the result of an expression is an important part of programming,
> > allowing a descriptive name to be used in place of a longer expression,
> > and permitting reuse. Currently, this feature is available only in
> > statement form, making it unavailable in list comprehensions and other
> > expression contexts. Merely introducing a way to assign as an expression
> > would create bizarre edge cases around comprehensions, though, and to
> avoid
> > the worst of the confusions, we change the definition of comprehensions,
> > causing some edge cases to be interpreted differently, but maintaining
> the
> > existing behaviour in the majority of situations.
> >
> >
> > Syntax and semantics
> > ====================
> >
> > In any context where arbitrary Python expressions can be used, a **named
> > expression** can appear. This is of the form ``target := expr`` where
> > ``expr`` is any valid Python expression, and ``target`` is any valid
> > assignment target.
> >
> > The value of such a named expression is the same as the incorporated
> > expression, with the additional side-effect that the target is assigned
> > that value::
> >
> > # Handle a matched regex
> > if (match := pattern.search(data)) is not None:
> > ...
> >
> > # A more explicit alternative to the 2-arg form of iter() invocation
> > while (value := read_next_item()) is not None:
> > ...
> >
> > # Share a subexpression between a comprehension filter clause and its
> output
> > filtered_data = [y for x in data if (y := f(x)) is not None]
> >
> >
> > Differences from regular assignment statements
> > ----------------------------------------------
> >
> > Most importantly, since ``:=`` is an expression, it can be used in
> contexts
> > where statements are illegal, including lambda functions and
> comprehensions.
> >
> > An assignment statement can assign to multiple targets, left-to-right::
> >
> > x = y = z = 0
> >
> > The equivalent assignment expression is parsed as separate binary
> operators,
> > and is therefore processed right-to-left, as if it were spelled thus::
> >
> > assert 0 == (x := (y := (z := 0)))
> >
> > Augmented assignment is not supported in expression form::
> >
> >>>> x +:= 1
> > File "<stdin>", line 1
> > x +:= 1
> > ^
> > SyntaxError: invalid syntax
> >
> > Otherwise, the semantics of assignment are identical in statement and
> > expression forms.
> >
> >
> > Alterations to comprehensions
> > -----------------------------
> >
> > The current behaviour of list/set/dict comprehensions and generator
> > expressions has some edge cases that would behave strangely if an
> assignment
> > expression were to be used. Therefore the proposed semantics are changed,
> > removing the current edge cases, and instead altering their behaviour
> *only*
> > in a class scope.
> >
> > As of Python 3.7, the outermost iterable of any comprehension is
> evaluated
> > in the surrounding context, and then passed as an argument to the
> implicit
> > function that evaluates the comprehension.
> >
> > Under this proposal, the entire body of the comprehension is evaluated in
> > its implicit function. Names not assigned to within the comprehension are
> > located in the surrounding scopes, as with normal lookups. As one special
> > case, a comprehension at class scope will **eagerly bind** any name which
> > is already defined in the class scope.
> >
> > A list comprehension can be unrolled into an equivalent function. With
> > Python 3.7 semantics::
> >
> > numbers = [x + y for x in range(3) for y in range(4)]
> > # Is approximately equivalent to
> > def <listcomp>(iterator):
> > result = []
> > for x in iterator:
> > for y in range(4):
> > result.append(x + y)
> > return result
> > numbers = <listcomp>(iter(range(3)))
> >
> > Under the new semantics, this would instead be equivalent to::
> >
> > def <listcomp>():
> > result = []
> > for x in range(3):
> > for y in range(4):
> > result.append(x + y)
> > return result
> > numbers = <listcomp>()
> >
> > When a class scope is involved, a naive transformation into a function
> would
> > prevent name lookups (as the function would behave like a method)::
> >
> > class X:
> > names = ["Fred", "Barney", "Joe"]
> > prefix = "> "
> > prefixed_names = [prefix + name for name in names]
> >
> > With Python 3.7 semantics, this will evaluate the outermost iterable at
> class
> > scope, which will succeed; but it will evaluate everything else in a
> function::
> >
> > class X:
> > names = ["Fred", "Barney", "Joe"]
> > prefix = "> "
> > def <listcomp>(iterator):
> > result = []
> > for name in iterator:
> > result.append(prefix + name)
> > return result
> > prefixed_names = <listcomp>(iter(names))
> >
> > The name ``prefix`` is thus searched for at global scope, ignoring the
> class
> > name. Under the proposed semantics, this name will be eagerly bound; and
> the
> > same early binding then handles the outermost iterable as well. The list
> > comprehension is thus approximately equivalent to::
> >
> > class X:
> > names = ["Fred", "Barney", "Joe"]
> > prefix = "> "
> > def <listcomp>(names=names, prefix=prefix):
> > result = []
> > for name in names:
> > result.append(prefix + name)
> > return result
> > prefixed_names = <listcomp>()
> >
> > With list comprehensions, this is unlikely to cause any confusion. With
> > generator expressions, this has the potential to affect behaviour, as the
> > eager binding means that the name could be rebound between the creation
> of
> > the genexp and the first call to ``next()``. It is, however, more closely
> > aligned to normal expectations. The effect is ONLY seen with names that
> > are looked up from class scope; global names (eg ``range()``) will still
> > be late-bound as usual.
> >
> > One consequence of this change is that certain bugs in genexps will not
> > be detected until the first call to ``next()``, where today they would be
> > caught upon creation of the generator.
> >
> >
> > Recommended use-cases
> > =====================
> >
> > Simplifying list comprehensions
> > -------------------------------
> >
> > A list comprehension can map and filter efficiently by capturing
> > the condition::
> >
> > results = [(x, y, x/y) for x in input_data if (y := f(x)) > 0]
> >
> > Similarly, a subexpression can be reused within the main expression, by
> > giving it a name on first use::
> >
> > stuff = [[y := f(x), x/y] for x in range(5)]
> >
> > # There are a number of less obvious ways to spell this in current
> > # versions of Python, such as:
> >
> > # Inline helper function
> > stuff = [(lambda y: [y,x/y])(f(x)) for x in range(5)]
> >
> > # Extra 'for' loop - potentially could be optimized internally
> > stuff = [[y, x/y] for x in range(5) for y in [f(x)]]
> >
> > # Using a mutable cache object (various forms possible)
> > c = {}
> > stuff = [[c.update(y=f(x)) or c['y'], x/c['y']] for x in range(5)]
> >
> > In all cases, the name is local to the comprehension; like iteration
> variables,
> > it cannot leak out into the surrounding context.
> >
> >
> > Capturing condition values
> > --------------------------
> >
> > Assignment expressions can be used to good effect in the header of
> > an ``if`` or ``while`` statement::
> >
> > # Proposed syntax
> > while (command := input("> ")) != "quit":
> > print("You entered:", command)
> >
> > # Capturing regular expression match objects
> > # See, for instance, Lib/pydoc.py, which uses a multiline spelling
> > # of this effect
> > if match := re.search(pat, text):
> > print("Found:", match.group(0))
> >
> > # Reading socket data until an empty string is returned
> > while data := sock.read():
> > print("Received data:", data)
> >
> > # Equivalent in current Python, not caring about function return value
> > while input("> ") != "quit":
> > print("You entered a command.")
> >
> > # To capture the return value in current Python demands a four-line
> > # loop header.
> > while True:
> > command = input("> ");
> > if command == "quit":
> > break
> > print("You entered:", command)
> >
> > Particularly with the ``while`` loop, this can remove the need to have an
> > infinite loop, an assignment, and a condition. It also creates a smooth
> > parallel between a loop which simply uses a function call as its
> condition,
> > and one which uses that as its condition but also uses the actual value.
> >
> >
> > Rejected alternative proposals
> > ==============================
> >
> > Proposals broadly similar to this one have come up frequently on
> python-ideas.
> > Below are a number of alternative syntaxes, some of them specific to
> > comprehensions, which have been rejected in favour of the one given
> above.
> >
> >
> > Alternative spellings
> > ---------------------
> >
> > Broadly the same semantics as the current proposal, but spelled
> differently.
> >
> > 1. ``EXPR as NAME``::
> >
> > stuff = [[f(x) as y, x/y] for x in range(5)]
> >
> > Since ``EXPR as NAME`` already has meaning in ``except`` and ``with``
> > statements (with different semantics), this would create unnecessary
> > confusion or require special-casing (eg to forbid assignment within the
> > headers of these statements).
> >
> > 2. ``EXPR -> NAME``::
> >
> > stuff = [[f(x) -> y, x/y] for x in range(5)]
> >
> > This syntax is inspired by languages such as R and Haskell, and some
> > programmable calculators. (Note that a left-facing arrow ``y <- f(x)``
> is
> > not possible in Python, as it would be interpreted as less-than and
> unary
> > minus.) This syntax has a slight advantage over 'as' in that it does
> not
> > conflict with ``with`` and ``except`` statements, but otherwise is
> > equivalent.
> >
> > 3. Adorning statement-local names with a leading dot::
> >
> > stuff = [[(f(x) as .y), x/.y] for x in range(5)] # with "as"
> > stuff = [[(.y := f(x)), x/.y] for x in range(5)] # with ":="
> >
> > This has the advantage that leaked usage can be readily detected,
> removing
> > some forms of syntactic ambiguity. However, this would be the only
> place
> > in Python where a variable's scope is encoded into its name, making
> > refactoring harder.
> >
> > 4. Adding a ``where:`` to any statement to create local name bindings::
> >
> > value = x**2 + 2*x where:
> > x = spam(1, 4, 7, q)
> >
> > Execution order is inverted (the indented body is performed first,
> followed
> > by the "header"). This requires a new keyword, unless an existing
> keyword
> > is repurposed (most likely ``with:``). See PEP 3150 for prior
> discussion
> > on this subject (with the proposed keyword being ``given:``).
> >
> > 5. ``TARGET from EXPR``::
> >
> > stuff = [[y from f(x), x/y] for x in range(5)]
> >
> > This syntax has fewer conflicts than ``as`` does (conflicting only
> with the
> > ``raise Exc from Exc`` notation), but is otherwise comparable to it.
> Instead
> > of paralleling ``with expr as target:`` (which can be useful but can
> also be
> > confusing), this has no parallels, but is evocative.
> >
> >
> > Special-casing conditional statements
> > -------------------------------------
> >
> > One of the most popular use-cases is ``if`` and ``while`` statements.
> Instead
> > of a more general solution, this proposal enhances the syntax of these
> two
> > statements to add a means of capturing the compared value::
> >
> > if re.search(pat, text) as match:
> > print("Found:", match.group(0))
> >
> > This works beautifully if and ONLY if the desired condition is based on
> the
> > truthiness of the captured value. It is thus effective for specific
> > use-cases (regex matches, socket reads that return `''` when done), and
> > completely useless in more complicated cases (eg where the condition is
> > ``f(x) < 0`` and you want to capture the value of ``f(x)``). It also has
> > no benefit to list comprehensions.
> >
> > Advantages: No syntactic ambiguities. Disadvantages: Answers only a
> fraction
> > of possible use-cases, even in ``if``/``while`` statements.
> >
> >
> > Special-casing comprehensions
> > -----------------------------
> >
> > Another common use-case is comprehensions (list/set/dict, and genexps).
> As
> > above, proposals have been made for comprehension-specific solutions.
> >
> > 1. ``where``, ``let``, or ``given``::
> >
> > stuff = [(y, x/y) where y = f(x) for x in range(5)]
> > stuff = [(y, x/y) let y = f(x) for x in range(5)]
> > stuff = [(y, x/y) given y = f(x) for x in range(5)]
> >
> > This brings the subexpression to a location in between the 'for' loop
> and
> > the expression. It introduces an additional language keyword, which
> creates
> > conflicts. Of the three, ``where`` reads the most cleanly, but also
> has the
> > greatest potential for conflict (eg SQLAlchemy and numpy have ``where``
> > methods, as does ``tkinter.dnd.Icon`` in the standard library).
> >
> > 2. ``with NAME = EXPR``::
> >
> > stuff = [(y, x/y) with y = f(x) for x in range(5)]
> >
> > As above, but reusing the `with` keyword. Doesn't read too badly, and
> needs
> > no additional language keyword. Is restricted to comprehensions,
> though,
> > and cannot as easily be transformed into "longhand" for-loop syntax.
> Has
> > the C problem that an equals sign in an expression can now create a
> name
> > binding, rather than performing a comparison. Would raise the question
> of
> > why "with NAME = EXPR:" cannot be used as a statement on its own.
> >
> > 3. ``with EXPR as NAME``::
> >
> > stuff = [(y, x/y) with f(x) as y for x in range(5)]
> >
> > As per option 2, but using ``as`` rather than an equals sign. Aligns
> > syntactically with other uses of ``as`` for name binding, but a simple
> > transformation to for-loop longhand would create drastically different
> > semantics; the meaning of ``with`` inside a comprehension would be
> > completely different from the meaning as a stand-alone statement, while
> > retaining identical syntax.
> >
> > Regardless of the spelling chosen, this introduces a stark difference
> between
> > comprehensions and the equivalent unrolled long-hand form of the loop.
> It is
> > no longer possible to unwrap the loop into statement form without
> reworking
> > any name bindings. The only keyword that can be repurposed to this task
> is
> > ``with``, thus giving it sneakily different semantics in a comprehension
> than
> > in a statement; alternatively, a new keyword is needed, with all the
> costs
> > therein.
> >
> >
> > Lowering operator precedence
> > ----------------------------
> >
> > There are two logical precedences for the ``:=`` operator. Either it
> should
> > bind as loosely as possible, as does statement-assignment; or it should
> bind
> > more tightly than comparison operators. Placing its precedence between
> the
> > comparison and arithmetic operators (to be precise: just lower than
> bitwise
> > OR) allows most uses inside ``while`` and ``if`` conditions to be spelled
> > without parentheses, as it is most likely that you wish to capture the
> value
> > of something, then perform a comparison on it::
> >
> > pos = -1
> > while pos := buffer.find(search_term, pos + 1) >= 0:
> > ...
> >
> > Once find() returns -1, the loop terminates. If ``:=`` binds as loosely
> as
> > ``=`` does, this would capture the result of the comparison (generally
> either
> > ``True`` or ``False``), which is less useful.
> >
> > While this behaviour would be convenient in many situations, it is also
> harder
> > to explain than "the := operator behaves just like the assignment
> statement",
> > and as such, the precedence for ``:=`` has been made as close as
> possible to
> > that of ``=``.
> >
> >
> > Migration path
> > ==============
> >
> > The semantic changes to list/set/dict comprehensions, and more so to
> generator
> > expressions, may potentially require migration of code. In many cases,
> the
> > changes simply make legal what used to raise an exception, but there are
> some
> > edge cases that were previously legal and now are not, and a few corner
> cases
> > with altered semantics.
> >
> >
> > The Outermost Iterable
> > ----------------------
> >
> > As of Python 3.7, the outermost iterable in a comprehension is special:
> it is
> > evaluated in the surrounding context, instead of inside the
> comprehension.
> > Thus it is permitted to contain a ``yield`` expression, to use a name
> also
> > used elsewhere, and to reference names from class scope. Also, in a
> genexp,
> > the outermost iterable is pre-evaluated, but the rest of the code is not
> > touched until the genexp is first iterated over. Class scope is now
> handled
> > more generally (see above), but if other changes require the old
> behaviour,
> > the iterable must be explicitly elevated from the comprehension::
> >
> > # Python 3.7
> > def f(x):
> > return [x for x in x if x]
> > def g():
> > return [x for x in [(yield 1)]]
> > # With PEP 572
> > def f(x):
> > return [y for y in x if y]
> > def g():
> > sent_item = (yield 1)
> > return [x for x in [sent_item]]
> >
> > This more clearly shows that it is g(), not the comprehension, which is
> able
> > to yield values (and is thus a generator function). The entire
> comprehension
> > is consistently in a single scope.
> >
> > The following expressions would, in Python 3.7, raise exceptions
> immediately.
> > With the removal of the outermost iterable's special casing, they are now
> > equivalent to the most obvious longhand form::
> >
> > gen = (x for x in rage(10)) # NameError
> > gen = (x for x in 10) # TypeError (not iterable)
> > gen = (x for x in range(1/0)) # ZeroDivisionError
> >
> > def <genexp>():
> > for x in rage(10):
> > yield x
> > gen = <genexp>() # No exception yet
> > tng = next(gen) # NameError
> >
> >
> > Open questions
> > ==============
> >
> > Importing names into comprehensions
> > -----------------------------------
> >
> > A list comprehension can use and update local names, and they will retain
> > their values from one iteration to another. It would be convenient to use
> > this feature to create rolling or self-effecting data streams::
> >
> > progressive_sums = [total := total + value for value in data]
> >
> > This will fail with UnboundLocalError due to ``total`` not being
> initalized.
> > Simply initializing it outside of the comprehension is insufficient -
> unless
> > the comprehension is in class scope::
> >
> > class X:
> > total = 0
> > progressive_sums = [total := total + value for value in data]
> >
> > At other scopes, it may be beneficial to have a way to fetch a value
> from the
> > surrounding scope. Should this be automatic? Should it be controlled
> with a
> > keyword? Hypothetically (and using no new keywords), this could be
> written::
> >
> > total = 0
> > progressive_sums = [total := total + value
> > import nonlocal total
> > for value in data]
> >
> > Translated into longhand, this would become::
> >
> > total = 0
> > def <listcomp>(total=total):
> > result = []
> > for value in data:
> > result.append(total := total + value)
> > return result
> > progressive_sums = <listcomp>()
> >
> > ie utilizing the same early-binding technique that is used at class
> scope.
> >
> >
> > Frequently Raised Objections
> > ============================
> >
> > Why not just turn existing assignment into an expression?
> > ---------------------------------------------------------
> >
> > C and its derivatives define the ``=`` operator as an expression, rather
> than
> > a statement as is Python's way. This allows assignments in more
> contexts,
> > including contexts where comparisons are more common. The syntactic
> similarity
> > between ``if (x == y)`` and ``if (x = y)`` belies their drastically
> different
> > semantics. Thus this proposal uses ``:=`` to clarify the distinction.
> >
> >
> > This could be used to create ugly code!
> > ---------------------------------------
> >
> > So can anything else. This is a tool, and it is up to the programmer to
> use it
> > where it makes sense, and not use it where superior constructs can be
> used.
> >
> >
> > With assignment expressions, why bother with assignment statements?
> > -------------------------------------------------------------------
> >
> > The two forms have different flexibilities. The ``:=`` operator can be
> used
> > inside a larger expression; the ``=`` statement can be augmented to
> ``+=`` and
> > its friends. The assignment statement is a clear declaration of intent:
> this
> > value is to be assigned to this target, and that's it.
> >
> >
> > Why not use a sublocal scope and prevent namespace pollution?
> > -------------------------------------------------------------
> >
> > Previous revisions of this proposal involved sublocal scope (restricted
> to a
> > single statement), preventing name leakage and namespace pollution.
> While a
> > definite advantage in a number of situations, this increases complexity
> in
> > many others, and the costs are not justified by the benefits. In the
> interests
> > of language simplicity, the name bindings created here are exactly
> equivalent
> > to any other name bindings, including that usage at class or module
> scope will
> > create externally-visible names. This is no different from ``for``
> loops or
> > other constructs, and can be solved the same way: ``del`` the name once
> it is
> > no longer needed, or prefix it with an underscore.
> >
> > Names bound within a comprehension are local to that comprehension, even
> in
> > the outermost iterable, and can thus be used freely without polluting the
> > surrounding namespace.
> >
> > (The author wishes to thank Guido van Rossum and Christoph Groth for
> their
> > suggestions to move the proposal in this direction. [2]_)
> >
> >
> > Style guide recommendations
> > ===========================
> >
> > As this adds another way to spell some of the same effects as can
> already be
> > done, it is worth noting a few broad recommendations. These could be
> included
> > in PEP 8 and/or other style guides.
> >
> > 1. If either assignment statements or assignment expressions can be
> > used, prefer statements; they are a clear declaration of intent.
> >
> > 2. If using assignment expressions would lead to ambiguity about
> > execution order, restructure it to use statements instead.
> >
> >
> > Acknowledgements
> > ================
> >
> > The author wishes to thank Guido van Rossum and Nick Coghlan for their
> > considerable contributions to this proposal, and to members of the
> > core-mentorship mailing list for assistance with implementation.
> >
> >
> > References
> > ==========
> >
> > .. [1] Proof of concept / reference implementation
> > (https://github.com/Rosuav/cpython/tree/assignment-expressions)
> > .. [2] Pivotal post regarding inline assignment semantics
> > (https://mail.python.org/pipermail/python-ideas/2018-March/049409.html
> )
> >
> >
> > Copyright
> > =========
> >
> > This document has been placed in the public domain.
> >
> >
> > ..
> > Local Variables:
> > mode: indented-text
> > indent-tabs-mode: nil
> > sentence-end-double-space: t
> > fill-column: 70
> > coding: utf-8
> > End:
> > _______________________________________________
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> > Unsubscribe: https://mail.python.org/mailman/options/python-dev/
> damalinov%40gmail.com
>
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>
--
--Guido van Rossum (python.org/~guido)
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