Re: [Python-ideas] A comprehension scope issue in PEP 572

For what it's worth, i'm totally +1 on inline uses of global and nonlocal. As a related improvement, i'd also like it if "global x = 5" would be a legal statement. As a noob learning python, I was suprised to find out I couldn't and had to split it on two lines.(aside from a 9-hour course of C

Re: [Python-ideas] Runtime assertion with no overhead when not active

I didn't mean to replace the current (debug) assert but I wanted to add another one that would allow to be switch on or off on production builds. The need for a new keyword (not syntax) comes from this difference. I cannot think of another example that would convince you of the benefit of

Re: [Python-ideas] __dir__ in which folder is this py file

On Sun, May 06, 2018 at 09:33:03PM -0700, Nathaniel Smith wrote: > How is > > data_path = __filepath__.parent / "foo.txt" > > more distracting than > > data_path = joinpath(dirname(__file__), "foo.txt") Why are you dividing by a string? That's weird. [looks up the pathlib docs] Oh, that's

Re: [Python-ideas] A comprehension scope issue in PEP 572

On Mon, May 7, 2018 at 9:42 PM, Steven D'Aprano wrote: > On Mon, May 07, 2018 at 12:48:53PM +1000, Chris Angelico wrote: >> On Mon, May 7, 2018 at 12:34 PM, Tim Peters wrote: > >> > There's a difference, though: if `y` "leaks", BFD. Who cares? ;-) >>

Re: [Python-ideas] __dir__ in which folder is this py file

On Mon, May 7, 2018 at 8:44 PM, Steven D'Aprano wrote: > On Sun, May 06, 2018 at 09:33:03PM -0700, Nathaniel Smith wrote: > >> How is >> >> data_path = __filepath__.parent / "foo.txt" >> >> more distracting than >> >> data_path = joinpath(dirname(__file__), "foo.txt") > > >

Re: [Python-ideas] A comprehension scope issue in PEP 572

On Mon, May 07, 2018 at 12:48:53PM +1000, Chris Angelico wrote: > On Mon, May 7, 2018 at 12:34 PM, Tim Peters wrote: > > There's a difference, though: if `y` "leaks", BFD. Who cares? ;-) > > If `y` remains inaccessible, there's no way around that. > > That's Steve

Re: [Python-ideas] __dir__ in which folder is this py file

On 7 May 2018 at 21:42, Nathaniel Smith wrote: > On Mon, May 7, 2018, 03:45 Steven D'Aprano wrote: > >> On Sun, May 06, 2018 at 09:33:03PM -0700, Nathaniel Smith wrote: >> >> > How is >> > >> > data_path = __filepath__.parent / "foo.txt" >> > >> > more

Re: [Python-ideas] Runtime assertion with no overhead when not active

On Sun, 2018-05-06 at 01:30 +1000, Steven D'Aprano wrote: > On Sat, May 05, 2018 at 08:04:45AM +, Eloi Gaudry wrote: > > > Hi folks, > > I intend to add a runtime assertion feature in python. > > I'm very interested in this idea, but I'm afraid your draft PEP > isn't  > very clear about this

Re: [Python-ideas] Runtime assertion with no overhead when not active

07.05.18 12:58, Eloi Gaudry пише: I didn't mean to replace the current (debug) assert but I wanted to add another one that would allow to be switch on or off on production builds. The need for a new keyword (not syntax) comes from this difference.  I cannot think of another example that

Re: [Python-ideas] __dir__ in which folder is this py file

On Mon, May 7, 2018, 03:45 Steven D'Aprano wrote: > On Sun, May 06, 2018 at 09:33:03PM -0700, Nathaniel Smith wrote: > > > How is > > > > data_path = __filepath__.parent / "foo.txt" > > > > more distracting than > > > > data_path = joinpath(dirname(__file__), "foo.txt") > >

Re: [Python-ideas] __dir__ in which folder is this py file

On 7 May 2018 at 20:44, Steven D'Aprano wrote: > First I have to work out what __filepath__ is, then I have to remember > the differences between all the various flavours of pathlib.Path > and suffer a moment or two of existential dread as I try to work out > whether or not

Re: [Python-ideas] __dir__ in which folder is this py file

06.05.18 09:53, Yuval Greenfield пише: I often need to reference a script's current directory. I end up writing: import os SRC_DIR = os.path.dirname(__file__) But I would prefer to have a new dunder for that. I propose: "__dir__". I was wondering if others would find it convenient to

Re: [Python-ideas] A comprehension scope issue in PEP 572

On Mon, May 07, 2018 at 10:38:51PM +1000, Chris Angelico wrote: > On Mon, May 7, 2018 at 9:42 PM, Steven D'Aprano wrote: [...] > > (3) A compromise: binding assignments are scoped local to the > > comprehension, but they are initialised from their surrounding scope. [...] >

Re: [Python-ideas] __dir__ in which folder is this py file

07.05.18 17:42, Eric Snow пише: I'm not necessarily saying we should add ModuleSpec.dirname(), but it (or something like it) is what I'd advocate for *if* we were to add a convenient shortcut to the directory a module is in. FWIW, I'd probably use it. The question is *why* you need the

[Python-ideas] Allow mutable builtin types (optionally)

Hi, I'd like to bring back this discussion (from 2005, by Greg): https://bugs.python.org/issue1229239 Briefly, non-heap types cannot have their attributes changed by Python code. This makes sense for python builtin types, but not for the types defined in extension/modules. As we have been using

Re: [Python-ideas] __dir__ in which folder is this py file

On Mon, May 7, 2018 at 7:14 AM, Serhiy Storchaka wrote: > * Additional burden on maintainers of import machinery. It is already too > complex, and __file__ is set in multiple places. Don't forgot about > third-party implementations. > > See also issue33277: "Deprecate

Re: [Python-ideas] string method count()

Regular expressions are not just "an order of magnitude better"—they're asymptotically faster. See https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm for a non-regular-expression algorithm. On Thursday, April 26, 2018 at 5:45:20 AM UTC-4, Jacco van Dorp wrote: > > or

Re: [Python-ideas] A comprehension scope issue in PEP 572

On 5/7/2018 1:38 PM, Guido van Rossum wrote: I am convinced by Tim's motivation. I hadn't thought of this use case before -- I had mostly thought "local scope in a comprehension or generator expression is the locals of the synthetic function". But Tim's reasoning feels right. The only

Re: [Python-ideas] Add "default" kw argument to operator.itemgetter and operator.attrgetter

(1) On 7 May 2018 at 01:07, Raymond Hettinger wrote: > He could've written: > > get = rpartial(getattr, 'foo', None) > return get(args) or get(config) or get(env) > That's somewhat hybrid, it would behave like: lambda obj: getattr(obj, "foo", None), but

Re: [Python-ideas] A comprehension scope issue in PEP 572

[Tim] > While I don't have real use cases beyond that, given that much, > "consistency" kicks in to suggest that: > > def f(): > [x := 42 for x in range(1)] > > makes `x` local to `f` despite that x wasn't bound elsewhere in f's body. > > def f(): > global x > [x

Re: [Python-ideas] Allow mutable builtin types (optionally)

On 05/07/18 11:37, Eloi Gaudry wrote: Hi, I'd like to bring back this discussion (from 2005, by Greg): https://bugs.python.org/issue1229239 Briefly, non-heap types cannot have their attributes changed by Python code. This makes sense for python builtin types, but not for the types defined in

Re: [Python-ideas] A comprehension scope issue in PEP 572

[Terry Reedy ] > ... > If I am understanding correctly, this would also let one *intentionally > 'leak' (export) the last value of the loop variable when wanted. > > [math.log(xlast:=x) for x in it if x > 0] > print(xlast) Yup! You can do that today by emulating a nonlocal

Re: [Python-ideas] __dir__ in which folder is this py file

Yuval Greenfield wrote: I often need to reference a script's current directory. I end up writing: import os SRC_DIR = os.path.dirname(__file__) The question I have is, why do you want to reference the script's current directory? If the answer is to access other files in that directory,

Re: [Python-ideas] A cute Python implementation of itertools.tee

I posted this several weeks ago, just for fun - an obscure but surprisingly brief Python implementation of itertools.tee, sharing a single stream (as a singly linked list) among all the returned iterables. Didn't think about it again until today, when recent discussions of lexical scoping made me

Re: [Python-ideas] A comprehension scope issue in PEP 572

On Mon, May 07, 2018 at 10:38:09AM -0700, Guido van Rossum wrote: > The only solution that makes sense to me is Steven's (2). (1) is what the > PEP currently says and what Tim doesn't want; (3) has no precedent > (function defaults don't really work like this) and just gets my hackles > all up.

[Python-ideas] Please consider skipping hidden directories in os.walk, os.fwalk, etc.

In a lot of uses of os.walk it is desirable to skip version control directories, (which are usually hidden directories), to the point that almost all of the examples given look like: import os for root, dirs, files in os.walk(some_dir): if 'CVS' in dirs: dirs.remove('CVS') # or

Re: [Python-ideas] A comprehension scope issue in PEP 572

[Tim] > ... The ":= is treated specially in comprehensions" idea is aimed > more at them than at people who think invoking a synthetic > anonymous lambda "is obvious". It occurs to me that, while suggestive, this is an unhelpful way to express it. It's not at all that the semantics of ":="

Re: [Python-ideas] A comprehension scope issue in PEP 572

On 2018-05-06 18:32, Tim Peters wrote: In a different thread I noted that I sometimes want to write code like this: while any(n % p == 0 for p in small_primes): # divide p out - but what's p? But generator expressions hide the value of `p` that succeeded, so I can't. `any()` and

Re: [Python-ideas] Add "default" kw argument to operator.itemgetter and operator.attrgetter

Hi everybody, > Have you encountered situations yourself where this would make a difference ? I need to get multiple objects in several dicts using the same set of keys. I wanted to use itemgetter to reduce the number of lines of code but I have mixed up getattr/dict.get that have default

Re: [Python-ideas] A comprehension scope issue in PEP 572

[Guido] > I am convinced by Tim's motivation. I hadn't thought of this use case before > -- I had mostly thought "local scope in a comprehension or generator > expression is the locals of the synthetic function". But Tim's reasoning > feels right. I'm trying very hard _not_ to reason. That is,

Re: [Python-ideas] A comprehension scope issue in PEP 572

[Tim] >> In a different thread I noted that I sometimes want to write code like >> this: >> >> while any(n % p == 0 for p in small_primes): >> # divide p out - but what's p? >> >> But generator expressions hide the value of `p` that succeeded, so I >> can't. `any()` and `all()`

Re: [Python-ideas] __dir__ in which folder is this py file

On Mon, May 07, 2018 at 11:42:00AM +, Nathaniel Smith wrote: > On Mon, May 7, 2018, 03:45 Steven D'Aprano wrote: [...] > > So yes, its very distracting. > > Well, yes, you do have to know the API to use it, and if you happen to have > learned the os.path API but not the

Re: [Python-ideas] A comprehension scope issue in PEP 572

On Tue, May 8, 2018 at 12:26 AM, Steven D'Aprano wrote: > Here's a sketch of how I think locals are currently handled: > > 1. When a function is compiled, the compiler does a pass over the >source and determines which locals are needed. > > 2. The compiler builds an array

Re: [Python-ideas] __dir__ in which folder is this py file

On Sun, May 6, 2018 at 9:30 PM, Mike Miller wrote: > On 2018-05-06 19:13, Nick Coghlan wrote: > >> Specifically, the ones I'd have in mind would be: >> >> - dirname (aka os.path.dirname) >> - joinpath (aka os.path.join) >> - abspath (aka os.path.abspath) >> > Yes, I

Re: [Python-ideas] Runtime assertion with no overhead when not active

On Mon, 7 May 2018 at 06:28 Serhiy Storchaka wrote: > 07.05.18 12:58, Eloi Gaudry пише: > > I didn't mean to replace the current (debug) assert but I wanted to add > > another one that would allow to be switch on or off on production builds. > > > > The need for a new

Re: [Python-ideas] __dir__ in which folder is this py file

On Mon, 7 May 2018 at 08:17 Serhiy Storchaka wrote: > 07.05.18 17:42, Eric Snow пише: > > I'm not necessarily saying we should add ModuleSpec.dirname(), but it > > (or something like it) is what I'd advocate for *if* we were to add a > > convenient shortcut to the directory

Re: [Python-ideas] __dir__ in which folder is this py file

On 2018-05-07 09:17, Steven D'Aprano wrote: I'm arguing that for some people, your preferred syntax*is* more distracting and hard to comprehend than the more self-descriptive version with named functions. And its not just a matter of*learning* the API, it is a matter of using it so often that

Re: [Python-ideas] A comprehension scope issue in PEP 572

I am convinced by Tim's motivation. I hadn't thought of this use case before -- I had mostly thought "local scope in a comprehension or generator expression is the locals of the synthetic function". But Tim's reasoning feels right. The only solution that makes sense to me is Steven's (2). (1) is

Re: [Python-ideas] Runtime assertion with no overhead when not active

On Mon, May 7, 2018 at 6:24 AM, Serhiy Storchaka wrote: > I just don't understand why you need a new keyword for writing runtime > checks. > Oh, that's pretty clear. The OP wants to be able to turn these checks off with some flag he can set/clear at runtime, and when it's

Re: [Python-ideas] Inline assignments using "given" clauses

On Fri, 4 May 2018 at 05:07 Nick Coghlan wrote: > (Note: Guido's already told me off-list that he doesn't like the way this > spelling reads, but I wanted to share it anyway since it addresses one of > the recurring requests in the PEP 572 discussions for a more targeted >