[issue28009] core logic of uuid.getnode() is broken for AIX - all versions

[Michael Felt]

Michael Felt  added the comment:

On 14/01/2018 22:01, Antoine Pitrou wrote:
> Antoine Pitrou  added the comment:
>
> Is nohup required in the example you just posted or is that a red herring?
>
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>
nohup is required (i.e., my lazy way!) to stream both stdout and stderr 
through the pipe. Perhaps, for this output nohup could have been 
omitted. But it became a habit while I was testing. Maybe a birthday 
herring :p

Working on the Windows issue (my mistake). Will be groping in the dark 
as I have no windows system to test on.

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Re: Detecting a cycle in a graph

[Frank Millman]

"Christian Gollwitzer"  wrote in message news:p3gh84$kfm$1...@dont-email.me...


Am 14.01.18 um 22:04 schrieb Christian Gollwitzer:
> Am 14.01.18 um 09:30 schrieb Frank Millman:
>> I need to detect when a 'cycle' occurs - when a path loops back on 
>> itself and revisits a node previously visited. I have figured out a way 
>> to do this, but I have a problem.

>
> I don't know if that helps, but there is a classic graph theory 
> algorithm called "Floyd's cycle detector". The idea is to have a pointer 
> move along the graph and a second one which runs at double the speed. If 
> they meet, you found a cycle. It is not straight-forward to come up with 
> this algorithm, which even runs in constant storage. ISTR that there are 
> some variants which can give you the split point of the cycle, too.


And here is an algorithm to enumerate all cycles in a directed graph:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.335.5999=rep1=pdf

with an implementation in C++ here:

https://github.com/hellogcc/circuit-finding-algorithm



I appreciate the input, Christian, but I am afraid both of those were over 
my head :-(


I think/hope that a business process graph does not require such a complex 
solution. Here is my cycle-detecting algorithm.


In BPMN terms, each node can have 0->* incoming connections, and 0->* 
outgoing connections.


Any node with 0 incoming is deemed to start the process. Normally there is 
only one such node.


Any node with 0 outgoing represents the end of an 'active path'. If there is 
more than one such node, all 'active' ones must reach the end before the 
process is finished. There is no formal definition of an 'active path', and 
I can think of a few corner cases which could prove problematic, but 
normally the meaning is clear.


I start my cycle-detection with a node with 0 incoming connections.

def find_cycle(node, path):
   for output in node.outputs:
   if output in path:
   print('Cycle found in', path)
   else:
   new_path = path[:]
   new_path.append(output)
   find_cycle(output, new_path)

find_cycle(node, [node])

This traverses every possible path in the graph. I think/hope that a typical 
business process will not grow so large as to cause a problem.


If anyone can see a flaw in this, please let me know.

Frank


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[issue15221] os.path.is*() may return False if path can't be accessed

[Mariatta Wijaya]

Mariatta Wijaya  added the comment:

Thanks!

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status: open -> closed

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[issue15221] os.path.is*() may return False if path can't be accessed

[Mariatta Wijaya]

Mariatta Wijaya  added the comment:


New changeset bb80645d06c16461b0b58d8983cd7fa6962ba3c6 by Mariatta (Miss 
Islington (bot)) in branch '3.6':
bpo-15221: Update os.path.is*() documentation (GH-5185) (GH-5186)
https://github.com/python/cpython/commit/bb80645d06c16461b0b58d8983cd7fa6962ba3c6


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[issue32553] venv says to use python3 which does not exist in 3.6.4

[Mariatta Wijaya]

Mariatta Wijaya  added the comment:

People who has more than one Python versions installed will have python3.

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[issue32551] 3.5.4 has a regression that was fixed in 3.6.1rc1

[Larry Hastings]

Larry Hastings  added the comment:

As a reminder: I'm currently scheduled to tag Python 3.5.5rc1 on January 21st, 
2018, aka about six days from now.

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[issue26330] shutil.disk_usage() on Windows can't properly handle unicode

[Roundup Robot]

Change by Roundup Robot :


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[issue26330] shutil.disk_usage() on Windows can't properly handle unicode

[Mariatta Wijaya]

Mariatta Wijaya  added the comment:


New changeset ee3b83547c6b0cac1da2cb44aaaea533a1d1bbc8 by Mariatta (Cheryl 
Sabella) in branch 'master':
bpo-26330: Update shutil.disk_usage() documentation (GH-5184)
https://github.com/python/cpython/commit/ee3b83547c6b0cac1da2cb44aaaea533a1d1bbc8


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[issue26163] FAIL: test_hash_effectiveness (test.test_set.TestFrozenSet)

[Raymond Hettinger]

Change by Raymond Hettinger :


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[issue15221] os.path.is*() may return False if path can't be accessed

[Roundup Robot]

Change by Roundup Robot :


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[issue15221] os.path.is*() may return False if path can't be accessed

[Mariatta Wijaya]

Mariatta Wijaya  added the comment:


New changeset b3dd18d4035803b50c65a434955966d1b3b1f363 by Mariatta (Cheryl 
Sabella) in branch 'master':
bpo-15221: Update os.path.is*() documentation (GH-5185)
https://github.com/python/cpython/commit/b3dd18d4035803b50c65a434955966d1b3b1f363


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Re: Why does pylint give this warning?

[breamoreboy]

On Sunday, January 14, 2018 at 10:32:44 PM UTC, Skip Montanaro wrote:
> > I cannot replicate this with
> >
> > $ pylint --version
> > Using config file /home/petto/.pylintrc
> > pylint 1.8.1,
> > astroid 1.6.0
> > Python 3.4.0 (default, Apr 11 2014, 13:05:11)
> > [GCC 4.8.2]
> >
> > $ cat pylint_fodder.py
> > class FooBar:
> > def __len__(self):
> > return 42
> > def __repr__(self):
> > return "FooBar(length={})".format(len(self))
> >
> > $ pylint pylint_fodder.py
> > Using config file /home/petto/.pylintrc
> > * Module pylint_fodder
> > C:  1, 0: Missing module docstring (missing-docstring)
> > C:  1, 0: Missing class docstring (missing-docstring)
> > R:  1, 0: Too few public methods (0/2) (too-few-public-methods)
> 
> Ditto. Mark, do you have any tweaks in your .pylintrc file which might
> affect it?
> 
> Skip

Having followed Peter's advice everything worked a treat once I'd put my 
changes  into the new configuration file.  Having compared it to the old one it 
looks as if I'd upgraded pylint but didn't regenerate the config file, as there 
were a number of obvious changes.  Thanks for the help guys, and if nothing 
else this is on the record for anyone with the same or similar problems.

--
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[issue26163] FAIL: test_hash_effectiveness (test.test_set.TestFrozenSet)

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Bringing this tracker item back to life.  I've had more time to look at the 
this and the underlying problem was the high bits were not being shuffled back 
to impact lower bits.  By fixing this, all of the tests produce a greater 
number of distinct values than before.

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[issue32551] 3.5.4 has a regression that was fixed in 3.6.1rc1

[Nick Coghlan]

Nick Coghlan  added the comment:

Unfortunately, it looks like bpo-29319 was backported to the 3.5 branch, but 
not the follow-up fix from bpo-29723: 
https://github.com/python/cpython/commits/3.5/Modules/main.c

(The metadata on bpo-29319 indicated that the original change was targeted at 
3.6+ only, and I didn't notice the message that mentioned the 3.5 branch, so I 
never even looked at 3.5 when working on bpo-29723 - I just assumed it wasn't 
affected)

Adding unexpected directories to sys.path can definitely be a security problem, 
so I think the fix should be backported for 3.5.5, but I'm also wondering 
whether it might be a significant enough regression to warrant an extra "Oops, 
sorry, we broke it" binary release. (We don't have any good usage numbers on 
how often folks use directory execution vs other forms of execution, so we 
don't know how widespread any impact is likely to be)

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Re: Where is the usage of (list comprehension) documented?

[Dan Stromberg]

On Sun, Jan 14, 2018 at 3:01 PM, Peng Yu  wrote:
> Hi,
>
> I see the following usage of list comprehension can generate a
> generator. Does anybody know where this is documented? Thanks.

Here's the (a?) generator expression PEP:
https://www.python.org/dev/peps/pep-0289/

Here's a presentation I put together on this and related topics a while back:
http://stromberg.dnsalias.org/~strombrg/Intro-to-Python/Python%20Generators,%20Iterators%20and%20Comprehensions%202014.pdf

FWIW, [a for a in range(2)] is a list comprehension; it's eager. And
(a for a in range(2)) is a generator expression; it's lazy.

HTH
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[issue32553] venv says to use python3 which does not exist in 3.6.4

[Paul Watson]

New submission from Paul Watson :

The 3.6.4 documentation on venv specifies using 'python3', but no python3 
executable is in the 3.6.4 kit.

https://docs.python.org/3/library/venv.html?highlight=venv#module-venv

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components: Documentation
messages: 309943
nosy: Paul Watson, docs@python
priority: normal
severity: normal
status: open
title: venv says to use python3 which does not exist in 3.6.4
type: enhancement
versions: Python 3.6

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[issue32542] memory not freed, aka memory leak continues...

[Michael Felt]

Michael Felt  added the comment:

Thanks for the clarification. 

Being curious, is there a way to see what the size of the cache is? I want to 
believe, but i do not have the impression memory is being reallocated to later 
users. My gut feeling is that the code change permits repeated calls to a 
function in a way that it reuses memory it received before (rather than a 
memory leak of repeatedly allocating a brand new buffer). What I expected, more 
accurately hoped for, is that cache was either freed and/or made available for 
reuse. 

Since I am on my phone atm I am less successful at finding documentation. I 
would be very grateful for a link to the relevant information and I’ll look 
further, time permitting. Thx again,

Michael 

Sent from my iPhone

> On 12 Jan 2018, at 23:48, Serhiy Storchaka  wrote:
> 
> 
> Serhiy Storchaka  added the comment:
> 
> Issue25582 fixed a memory leak. If run the tests repeatedly every iteration 
> leaked 100 MB of memory. If you get a MemoryError with a single iteration, 
> this means that your machine just doesn't have enough memory for tests. Tests 
> require around 500-600MB of memory on 32-bit platform.
> 
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Re: Where is the usage of (list comprehension) documented?

[Ben Finney]

Peng Yu  writes:

> > When you use square brackets, you're creating a generator, as in your
> > second example. Your first example is a slightly different beast
> > called a "generator expression". If you search for that in the docs or
> > on the web, you'll find what you want.
>
> Thanks. Can the documentation be found by `help()` in python?

The ‘help’ command is not intended to provide comprehensive user
documentation. Rather, it is intended primarily to provide a reminder of
syntax and purpose of specific API. It is not a replacement for having
the Python documentation available.

-- 
 \  “The history of Western science confirms the aphorism that the |
  `\ great menace to progress is not ignorance but the illusion of |
_o__)knowledge.” —Daniel J. Boorstin, historian, 1914–2004 |
Ben Finney

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Re: Where is the usage of (list comprehension) documented?

[Peng Yu]

> When you use square brackets, you're creating a generator, as in your
> second example. Your first example is a slightly different beast
> called a "generator expression". If you search for that in the docs or
> on the web, you'll find what you want.

Thanks. Can the documentation be found by `help()` in python?

-- 
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Peng
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[issue26330] shutil.disk_usage() on Windows can't properly handle unicode

[Eryk Sun]

Eryk Sun  added the comment:

This is the high-level shutil module, so why not try to use the resolved parent 
directory? For example:

def disk_usage(path):
try:
total, free = nt._getdiskusage(path)
except NotADirectoryError:
path = os.path.dirname(nt._getfinalpathname(path))
total, free = nt._getdiskusage(path)
used = total - free
return _ntuple_diskusage(total, used, free)

Also, as noted in msg260022, nt._getdiskusage was overlooked when implementing 
PEP 529. The same applies to nt._getfinalpathname and nt._getvolumepathname. 
nt._getfullpathname works with bytes because it takes an argument-clinic 
`path_t` instead of `unicode` or `Py_UNICODE`. I think the other 3 should be 
rewritten to use path_t, but it's out of scope for this issue.

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[issue32552] Improve text for file arguments in argparse.ArgumentDefaultsHelpFormatter class

[elypter]

New submission from elypter :

If you use formatter_class=argparse.ArgumentDefaultsHelpFormatter in the 
constructor then the defaults that you include in arguments get automatically 
added to the help text. this looks great for int and Strings but not for files.

example:
  -suffixes [SUFFIXES]
suffixes file which contains keywords that are often
the last part of a class or style name of a sticky bar
(default: )

it should rather look like

  -suffixes [SUFFIXES]
suffixes file which contains keywords that are often
the last part of a class or style name of a sticky bar
(default:'sources/suffixes.txt')


the same holds probably true for more exotic datatypes. so an alternative or an 
addition could be to add an option to arguments to not add the default to the 
help text

--
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messages: 309940
nosy: elypter
priority: normal
severity: normal
status: open
title: Improve text for file arguments in 
argparse.ArgumentDefaultsHelpFormatter class
versions: Python 3.4, Python 3.5, Python 3.6, Python 3.7, Python 3.8

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[issue15221] os.path.is*() may return False if path can't be accessed

[Cheryl Sabella]

Cheryl Sabella  added the comment:

I created a PR for this by making the word 'existing' a link to 
'os.path.exists' since Nick mentioned that that word already implied the 
definition.

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[issue15221] os.path.is*() may return False if path can't be accessed

[Cheryl Sabella]

Change by Cheryl Sabella :


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Re: Where is the usage of (list comprehension) documented?

[Chris Angelico]

On Mon, Jan 15, 2018 at 10:01 AM, Peng Yu  wrote:
> Hi,
>
> I see the following usage of list comprehension can generate a
> generator. Does anybody know where this is documented? Thanks.
>
> $ cat main.py
> #!/usr/bin/env python
>
> import sys
> lines = (line.rstrip('\n') for line in sys.stdin)
> print lines
>
> lines = [line.rstrip('\n') for line in sys.stdin]
> print lines
> $ seq 10 | ./main.py
>  at 0x1101ecd70>
> ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
>

When you use square brackets, you're creating a generator, as in your
second example. Your first example is a slightly different beast
called a "generator expression". If you search for that in the docs or
on the web, you'll find what you want.

ChrisA
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Where is the usage of (list comprehension) documented?

[Peng Yu]

Hi,

I see the following usage of list comprehension can generate a
generator. Does anybody know where this is documented? Thanks.

$ cat main.py
#!/usr/bin/env python

import sys
lines = (line.rstrip('\n') for line in sys.stdin)
print lines

lines = [line.rstrip('\n') for line in sys.stdin]
print lines
$ seq 10 | ./main.py
 at 0x1101ecd70>
['1', '2', '3', '4', '5', '6', '7', '8', '9', '10']

-- 
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Peng
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Re: Generating SVG from turtle graphics

[Niles Rogoff]

On Sun, 14 Jan 2018 16:32:53 +0400, Abdur-Rahmaan Janhangeer wrote:

> maybe save to .png then use another tool to svg

PNG is a bitmap format[1], so you can't covert it to an SVG (a vector 
format) without guessing things like the start/end points of the lines, 
their slopes, etc... not to mention things like arcs.

[1] RFC2083
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[issue32516] Add a shared library mechanism for win32

[Steve Dower]

Steve Dower  added the comment:

The more details you reveal, the less I want it to be an officially supported 
pattern :)

Perhaps you actually want an import hook? Brett can confirm, but I believe you 
can overwrite __loader__ in a package and change how submodules are loaded.

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Re: Why does pylint give this warning?

[Skip Montanaro]

> I cannot replicate this with
>
> $ pylint --version
> Using config file /home/petto/.pylintrc
> pylint 1.8.1,
> astroid 1.6.0
> Python 3.4.0 (default, Apr 11 2014, 13:05:11)
> [GCC 4.8.2]
>
> $ cat pylint_fodder.py
> class FooBar:
> def __len__(self):
> return 42
> def __repr__(self):
> return "FooBar(length={})".format(len(self))
>
> $ pylint pylint_fodder.py
> Using config file /home/petto/.pylintrc
> * Module pylint_fodder
> C:  1, 0: Missing module docstring (missing-docstring)
> C:  1, 0: Missing class docstring (missing-docstring)
> R:  1, 0: Too few public methods (0/2) (too-few-public-methods)

Ditto. Mark, do you have any tweaks in your .pylintrc file which might
affect it?

Skip
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Re: Why does pylint give this warning?

[Peter Otten]

breamore...@gmail.com wrote:

> Why does pylint give this warning?

No idea.

> The warning is 'C0103:Method name "__len__" doesn't conform to
> '_?_?[a-z][A-Za-z0-9]{1,30}$' pattern' but it doesn't complain about
> __repr__ or __str__.  If there is an explanation out in the wild my search
> fu has missed it :-(
> 
> My setup on Ubuntu 17.10 is:-
> 
> $ pylint --version
> Using config file /home/mark/.pylintrc
> pylint 1.8.1,
> astroid 1.6.0
> Python 3.6.3 (default, Oct  3 2017, 21:45:48)
> [GCC 7.2.0]
> 
> --
> Kindest regards.
> 
> Mark Lawrence.

I cannot replicate this with

$ pylint --version
Using config file /home/petto/.pylintrc
pylint 1.8.1, 
astroid 1.6.0
Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
[GCC 4.8.2]

$ cat pylint_fodder.py 
class FooBar:
def __len__(self):
return 42
def __repr__(self):
return "FooBar(length={})".format(len(self))

$ pylint pylint_fodder.py 
Using config file /home/petto/.pylintrc
* Module pylint_fodder
C:  1, 0: Missing module docstring (missing-docstring)
C:  1, 0: Missing class docstring (missing-docstring)
R:  1, 0: Too few public methods (0/2) (too-few-public-methods)

---
Your code has been rated at 4.00/10

$

so the complaint is probably caused by your configuration file.
Rename it, regenerate the default with

$ pylint --generate-rcfile > ~/.pylintrc

and reapply your changes -- I hope there aren't too many of them ;) -- until 
you see the warning message again.

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[issue15115] Duplicated Content-Transfer-Encoding header when applying email.encoders

[Cheryl Sabella]

Cheryl Sabella  added the comment:

Barry/David,

Is this still a change you wanted to include in the documentation?


Thanks!

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[issue26330] shutil.disk_usage() on Windows can't properly handle unicode

[Cheryl Sabella]

Change by Cheryl Sabella :


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[issue26330] shutil.disk_usage() on Windows can't properly handle unicode

[Cheryl Sabella]

Cheryl Sabella  added the comment:

I've submitted a PR for the documentation change.

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[issue26330] shutil.disk_usage() on Windows can't properly handle unicode

[Cheryl Sabella]

Change by Cheryl Sabella :


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Re: Detecting a cycle in a graph

[Christian Gollwitzer]

Am 14.01.18 um 22:04 schrieb Christian Gollwitzer:

Am 14.01.18 um 09:30 schrieb Frank Millman:
I need to detect when a 'cycle' occurs - when a path loops back on 
itself and revisits a node previously visited. I have figured out a 
way to do this, but I have a problem.


I don't know if that helps, but there is a classic graph theory 
algorithm called "Floyd's cycle detector". The idea is to have a pointer 
move along the graph and a second one which runs at double the speed. If 
they meet, you found a cycle. It is not straight-forward to come up with 
this algorithm, which even runs in constant storage. ISTR that there are 
some variants which can give you the split point of the cycle, too.


And here is an algorithm to enumerate all cycles in a directed graph:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.335.5999=rep1=pdf

with an implementation in C++ here:

https://github.com/hellogcc/circuit-finding-algorithm

Christian
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Why does pylint give this warning?

[breamoreboy]

The warning is 'C0103:Method name "__len__" doesn't conform to 
'_?_?[a-z][A-Za-z0-9]{1,30}$' pattern' but it doesn't complain about __repr__ 
or __str__.  If there is an explanation out in the wild my search fu has missed 
it :-(

My setup on Ubuntu 17.10 is:-

$ pylint --version
Using config file /home/mark/.pylintrc
pylint 1.8.1, 
astroid 1.6.0
Python 3.6.3 (default, Oct  3 2017, 21:45:48) 
[GCC 7.2.0]

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Mark Lawrence.
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Re: Detecting a cycle in a graph

[Christian Gollwitzer]

Am 14.01.18 um 09:30 schrieb Frank Millman:
I need to detect when a 'cycle' occurs - when a path loops back on 
itself and revisits a node previously visited. I have figured out a way 
to do this, but I have a problem.


I don't know if that helps, but there is a classic graph theory 
algorithm called "Floyd's cycle detector". The idea is to have a pointer 
move along the graph and a second one which runs at double the speed. If 
they meet, you found a cycle. It is not straight-forward to come up with 
this algorithm, which even runs in constant storage. ISTR that there are 
some variants which can give you the split point of the cycle, too.


Christian

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[issue28009] core logic of uuid.getnode() is broken for AIX - all versions

[Antoine Pitrou]

Antoine Pitrou  added the comment:

Is nohup required in the example you just posted or is that a red herring?

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[issue28009] core logic of uuid.getnode() is broken for AIX - all versions

[Michael Felt]

Michael Felt  added the comment:

FYI: - On AIX, no uuid_create support:

./python -m unittest -v test.test_uuid
...
Ran 48 tests in 0.261s

OK (skipped=37)

On AIX 6.1 (with ctypes, without _uuid)

./python -m unittest -v test.test_uuid
...
Ran 48 tests in 0.274s

OK (skipped=32)

On AIX 6.1 (with ctypes, with _uuid)

./python -m unittest -v test.test_uuid
...
Ran 48 tests in 0.379s

OK (skipped=16)

+++

nohup ./python -m unittest -v test.test_uuid | grep skipped
test_arp_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 'AIX 
arp does not provide MAC addr'
test_ifconfig_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 
'AIX ifconfig does not provide MAC addr'
test_ip_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 
'requires ip'
test_ipconfig_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 
'requires Windows'
test_lanscan_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 
'requires lanscan'
test_netbios_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 
'requires win32wnet'
test_windll_getnode (test.test_uuid.TestInternalsWithExtModule) ... skipped 
'requires Windows'
test_arp_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... skipped 
'AIX arp does not provide MAC addr'
test_ifconfig_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... 
skipped 'AIX ifconfig does not provide MAC addr'
test_ip_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... skipped 
'requires ip'
test_ipconfig_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... 
skipped 'requires Windows'
test_lanscan_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... skipped 
'requires lanscan'
test_netbios_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... skipped 
'requires win32wnet'
test_windll_getnode (test.test_uuid.TestInternalsWithoutExtModule) ... skipped 
'requires Windows'
test_uuid1_safe (test.test_uuid.TestUUIDWithExtModule) ... skipped 'requires 
uuid_generate_time_safe(3)'
test_uuid1_safe (test.test_uuid.TestUUIDWithoutExtModule) ... skipped 'requires 
uuid_generate_time_safe(3)'

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[issue28009] core logic of uuid.getnode() is broken for AIX - all versions

[Michael Felt]

Michael Felt  added the comment:

PR added, please review.

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[issue28009] core logic of uuid.getnode() is broken for AIX - all versions

[Michael Felt]

Change by Michael Felt :


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pull_requests: +5037
stage:  -> patch review

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[issue29476] Simplify set_add_entry()

[Raymond Hettinger]

Change by Raymond Hettinger :


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status: open -> closed

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[issue29476] Simplify set_add_entry()

[Raymond Hettinger]

Raymond Hettinger  added the comment:


New changeset 3329992e31bd0494a7d7312853f7ffd054737e27 by Raymond Hettinger in 
branch 'master':
bpo-29476: Simplify set_add_entry() (#5175)
https://github.com/python/cpython/commit/3329992e31bd0494a7d7312853f7ffd054737e27


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[issue29708] support reproducible Python builds

[Brett Cannon]

Brett Cannon  added the comment:

As Eli's comments are coming off as negative to/at me, I feel like I have
to defend myself here. If you look at the commit there was actually two
places where the timestamp was checked; one did an equality comparison and
one did a >= comparison. It's quite possible the semantics accidentally
changed as part of the refactoring due to the check being done in different
places and a different one was copied, although no one has even noticed
until now.

If there is a desire to change the semantics of how timestamps are checked
then that should be done in a separate issue as at this point we have lived
with the current semantics for several releases -- all releases of Python 3
still receiving security updates -- so it's passed being a bug and is now
the semantics in Python 3.

On Sat, Jan 13, 2018, 16:57 Eli Schwartz,  wrote:

>
> Eli Schwartz  added the comment:
>
> So, a couple of things.
>
> It seems to me, that properly supporting SOURCE_DATE_EPOCH means using
> exactly that and nothing else. To that end, I'm not entirely sure why
> things like --clamp-mtime even exist, as the original timestamp of a source
> file doesn't seem to have a lot of utility and it is better to be entirely
> predictable. But I'm not going to argue that, except insomuch as it seems
> IMHO to fit better for python to just keep things simple and override the
> timestamp with the value of SOURCE_DATE_EPOCH
>
> That being said, I see two problems with python implementing something
> analogous to --clamp-mtime rather than just --mtime.
>
>
> 1) Source files are extracted by some build process, and remain untouched.
> Python generates bytecode pinned to the original time, rather than
> SOURCE_DATE_EPOCH. Later, the build process packages those files and
> implements --mtime, not --clamp-mtime. Because Python and the packaging
> software disagree about which one to use, the bytecode fails.
>
> 2) Source files are extracted, and the build process even tosses all
> timestamps to the side of the road, by explicitly `touch`ing all of them to
> the date of SOURCE_DATE_EPOCH just in case. Then for whatever reason
> (distro patches, 2to3, the use of `cp`) the timestamps get updated to
> $currentime. But SOURCE_DATE_EPOCH is in the future, so the timestamps get
> downdated. Python bytecode is generated by emulating --clamp-mtime. The
> build process then uses --mtime to package the files. Again, because Python
> and the packaging software disagree about which one to use, the bytecode
> fails.
>
> Of course, in both those cases, blindly respecting SOURCE_DATE_EPOCH will
> seemingly break everything for people who use --clamp-mtime instead. I'm
> not happy with reproducible-builds.org for allowing either one.
>
> I don't think python should rely on --mtime users manually overriding the
> filesystem metadata of the source files outside of py_compile, as that is a
> hack that I think we'd like to remove if possible... that being said, Arch
> Linux will, on second thought, not be adversely affected even if py_compile
> tries to be clever and emulate --clamp-mtime to decide on its own whether
> to respect SOURCE_DATE_EPOCH.
>
> Likewise, I don't really expect people to try to reproduce builds using a
> future date for SOURCE_DATE_EPOCH. On the other hand, the reproducible
> builds spec doesn't forbid it AFAICT.
>
> But... neither of those mitigations seem "clean" to me, for the reasons
> stated above.
>
> There is something that would solve all these issues, though. From reading
> the importlib code (I haven't actually tried smoketesting actual imports),
> it appears that Python 2 accepts any bytecode that is dated at or later
> than the timestamp of its source .py, while Python 3 requires the
> timestamps to perfectly match. This seems bizarre to behave differently,
> especially as until @bmwiedemann mentioned it on the GitHub PR I blindly
> assumed that Python would not care if your bytecode is somehow dated later
> than your sources. If the user is playing monkey games with mismatched
> source and byte code, while backdating the source code to *trick* the
> interpreter into loading it... let them? They can break their stuff if they
> want to!
>
> On looking through the commit logs, it seems that Python 3 used to do the
> same, until
> https://github.com/python/cpython/commit/61b14251d3a653548f70350acb250cf23b696372
> refactored the general vicinity and modified this behavior without warning.
> In a commit that seems to be designed to do something else entirely. This
> really should have been two separate commits, and modifying the import code
> to more strictly check the timestamp should have come with an explanatory
> justification. Because I cannot think of a good reason for this behavior,
> and the commit isn't giving me an opportunity to understand either. As it
> is, I am completely confused, and have no idea whether this was even
> supposed to 

[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Raymond Hettinger]

Raymond Hettinger  added the comment:

I would like to see this patch go forward.  Making __annotations__ special and 
subtly different just adds to language complexity.

--
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[issue32534] Speed-up list.insert

[Raymond Hettinger]

Raymond Hettinger  added the comment:

The result likely varies quite a bit from compiler-to-compiler and 
processor-to-processor and os-to-os.   It is may also be affected by data size 
and caching.

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[issue32526] Closing async generator while it is running does not raise an exception

[Joongi Kim]

Change by Joongi Kim :


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Re: Generating SVG from turtle graphics

[Serhiy Storchaka]

11.01.18 13:03, Steven D'Aprano пише:

I'd like to draw something with turtle, then generate a SVG file from it.

Is this possible?

If not, is there something I can do which lets me plot lines, shapes and
curves and output to SVG?


You can translate the following Tcl/Tk recipe to Python/Tkinter: 
http://wiki.tcl.tk/4534. Or just run the code directly in the buildin 
Tcl interpreter.


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[issue32226] Implement PEP 560: Core support for typing module and generic types

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Sorry, I know very small about this module to writing the documentation.

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[issue32551] 3.5.4 has a regression that was fixed in 3.6.1rc1

[Ned Deily]

Change by Ned Deily :


--
dependencies: +3.6.1rc1 adds the current directory to sys.path when running a 
subdirectory's __main__.py; previous versions did not
nosy: +larry, ncoghlan

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[issue32551] 3.5.4 has a regression that was fixed in 3.6.1rc1

[Ned Batchelder]

Ned Batchelder  added the comment:

(For clarity)

The problem is that 3.5.4 adds the current directory to sys.path when running a 
subdirectory's __main__.py.  No other version of Python does this.

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[issue32551] 3.5.4 has a regression that was fixed in 3.6.1rc1

[Ned Batchelder]

New submission from Ned Batchelder :

The issue that I reported in https://bugs.python.org/issue29723 is now 
affecting 3.5.4:


```
$ pwd
/Users/ned/foo
$ tree syspathmain
syspathmain
└── __main__.py

0 directories, 1 file
$ cat syspathmain/__main__.py
import sys
print("-" * 20)
print(sys.version)
print("\n".join(sys.path))
$ for pyth in /usr/local/pythonz/pythons/CPython-*/bin/python; do $pyth 
syspathmain; done
/usr/local/pythonz/pythons/CPython-2.4.6/bin/python: 'syspathmain' is a 
directory, cannot continue

2.6.9 (unknown, Jun 18 2016, 17:45:44)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)]
syspathmain
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python26.zip
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/plat-darwin
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/plat-mac
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/plat-mac/lib-scriptpackages
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/lib-tk
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/lib-old
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/lib-dynload
/usr/local/pythonz/pythons/CPython-2.6.9/lib/python2.6/site-packages

2.7.10 (default, Jun 18 2016, 18:30:12)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)]
syspathmain
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python27.zip
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/plat-darwin
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/plat-mac
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/plat-mac/lib-scriptpackages
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/lib-tk
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/lib-old
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/lib-dynload
/usr/local/pythonz/pythons/CPython-2.7.10/lib/python2.7/site-packages

2.7.11 (default, Jun 18 2016, 17:51:44)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)]
syspathmain
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python27.zip
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/plat-darwin
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/plat-mac
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/plat-mac/lib-scriptpackages
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/lib-tk
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/lib-old
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/lib-dynload
/usr/local/pythonz/pythons/CPython-2.7.11/lib/python2.7/site-packages

2.7.12 (default, Nov 20 2016, 16:53:49)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)]
syspathmain
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python27.zip
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/plat-darwin
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/plat-mac
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/plat-mac/lib-scriptpackages
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/lib-tk
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/lib-old
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/lib-dynload
/usr/local/pythonz/pythons/CPython-2.7.12/lib/python2.7/site-packages

2.7.13 (default, Dec 17 2016, 16:51:07)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)]
syspathmain
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python27.zip
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/plat-darwin
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/plat-mac
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/plat-mac/lib-scriptpackages
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/lib-tk
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/lib-old
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/lib-dynload
/usr/local/pythonz/pythons/CPython-2.7.13/lib/python2.7/site-packages

2.7.13rc1 (default, Dec  4 2016, 15:34:21)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)]
syspathmain
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python27.zip
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/plat-darwin
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/plat-mac
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/plat-mac/lib-scriptpackages
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/lib-tk
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/lib-old
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/lib-dynload
/usr/local/pythonz/pythons/CPython-2.7.13rc1/lib/python2.7/site-packages

2.7.14 (default, Oct  4 2017, 09:45:53)
[GCC 4.2.1 

[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Mark Shannon]

Mark Shannon  added the comment:

Works as expected:

>>> class C:
... exec('x: int')
... 
>>> C.__annotations__
{'x': }
>>> __annotations__
{}

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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

There is also another corner case to consider:

class C:
exec('x: int')

assert C.__annotations__ == {'x': int}
assert __annotations__ == {}

I am not sure this one will be covered correctly.
But the main argument here is speed I think.

Let us see what others think about this.

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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Mark Shannon]

Mark Shannon  added the comment:

> 3. It doesn't add a name constant. Instead it uses a name from the names list 
> (which already has to contain this name).

This PR moves the constant for the name from `co_names` to `co_consts`. There 
is no duplication.
>>> def f():
...class C:
...   a : 1
(It does add __annotations__ to `co_names`, but that seems reasonable to me)

Current:
>>> f.__code__.co_consts[1].co_names
('__name__', '__module__', '__qualname__', 'a')
>>> f.__code__.co_consts[1].co_consts
('f..C', 1, None)
With PR 5181:
>>> f.__code__.co_consts[1].co_names
('__name__', '__module__', '__qualname__', '__annotations__')
>>> f.__code__.co_consts[1].co_consts
('f..C', 1, 'a', None)

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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Mark Shannon]

Mark Shannon  added the comment:

PEP 526 explicitly states
"as with all dunder attributes, any undocummented use of __annotations__ is 
subject to breakage without warning"

I consider deleting __annotations__ to be undocumented use.

Do you really think that an obscure difference in the behaviour of 

>>> class C:
... del __annotations__
... x: int

justifies an extra bytecode, but the implicit return at the end of all 
functions (LOAD_CONST None; RETURN_VALUE) does not?

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Re: Generating SVG from turtle graphics

[Abdur-Rahmaan Janhangeer]

maybe save to .png then use another tool to svg

On 11 Jan 2018 15:06, "Steven D'Aprano" <
steve+comp.lang.pyt...@pearwood.info> wrote:

> I'd like to draw something with turtle, then generate a SVG file from it.
>
> Is this possible?
>
> If not, is there something I can do which lets me plot lines, shapes and
> curves and output to SVG?
>
> Ideally, I'd like to draw a figure pixel by pixel, and then have the SVG
> library fit a bezier curve to it.
>
>
>
>
> --
> Steve
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>
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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

There are several corner cases. For example consider this code:

>>> class C:
... del __annotations__
... x: int

Currently this correctly raises NameError, with your replacement it will 
instead stick {'x': int} in the module `__annotations__`. I think there may be 
other special cases but I don't remember them now.

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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

There some subtle differences.

1. Unlike to LOAD_NAME, STORE_ANNOTATION doesn't fall back to globals if 
'__annotations__' is not found in locals. The behavior difference is shown by 
the following example:

x: int
class A:


del __annotations__ 

   
y: int

2. The single STORE_ANNOTATION is faster than 3 other opcodes.

3. It doesn't add a name constant. Instead it uses a name from the names list 
(which already has to contain this name).

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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Mark Shannon]

Change by Mark Shannon :


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pull_requests: +5034
stage: needs patch -> patch review

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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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[issue32550] STORE_ANNOTATION bytecode is unnecessary and can be removed.

[Mark Shannon]

New submission from Mark Shannon :

The STORE_ANNOTATION bytecode is used to implement annotations.
The code 
 name : ann
is equivalent to 
__annotations__['name'] = ann

Consequently,
STORE_ANNOTATION name

can be trivially replaced with 
LOAD_NAME  __annotations__
LOAD_CONST 'name'
STORE_SUBSCR

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components: Interpreter Core
messages: 309918
nosy: Mark.Shannon
priority: normal
severity: normal
stage: needs patch
status: open
title: STORE_ANNOTATION bytecode is unnecessary and can be removed.
type: enhancement
versions: Python 3.7

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Re: Detecting a cycle in a graph

[Frank Millman]

"Steven D'Aprano"  wrote in message news:p3f9uh$ar4$1...@blaine.gmane.org...


On Sun, 14 Jan 2018 10:30:31 +0200, Frank Millman wrote:

> I can detect a cycle in a path. It is possible for there to be more than
> one gateway in the path. I want to identify the gateway that actually
> triggered the cycle, but I have not figured out a way to do this.

You don't need a gateway to get a cycle. Suppose you have nodes

A -> B -> C -> D -> B

that's a cycle with no gateways.



[skip more good examples]



The usual way of fixing this sort of thing for systems intended for non-
expert use is to have a (user-configurable?) limit on the number of
steps, and have the process raise an error once it reaches the limit.

> After that, in the path returning to the previous node, there is another
> gateway that checks a counter. If the boolean check fails three times,
> terminate the process.

What boolean check? You mentioned a counter -- that's normally considered
to be an integer.



Sorry, I left out a couple of steps. In my imaginary process, every time the 
boolean check in the first gateway fails, it increments a counter. The 
second gateway checks the counter, and terminates the process if it exceeds 
a limit.



Try googling for "Halting problem" to learn why you cannot, in general,
prove that all cycles will eventually terminate. You may be able to
identify *some* non-terminating graphs, but you cannot determine all of
them.


I will do so. Thanks for clearing up some confusion and giving me some 
pointers.


Frank


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[issue32534] Speed-up list.insert

[Jeethu Rao]

Jeethu Rao  added the comment:

I managed to tune an i7700k desktop running Ubuntu 17.10 per this doc[1], and 
ran the pyperformance benchmarks[2].
I also tried various threshold with this benchmark and 16 still seems to be the 
sweet spot.
The geometric mean of the relative changes across all benchmarks indicates a 
12.85% improvement.

[1]: http://pyperformance.readthedocs.io/usage.html#how-to-get-stable-benchmarks
[2]: https://gist.github.com/jeethu/4d9a8bd3eecbd067c00f085f7d2e7595

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[issue32549] Travis: Test with OpenSSL 1.1.0

[Christian Heimes]

Change by Christian Heimes :


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[issue32549] Travis: Test with OpenSSL 1.1.0

[Christian Heimes]

New submission from Christian Heimes :

For several planned features and security improvements, at least OpenSSL 1.0.2 
is required. OpenSSL 1.1.0 is preferred to test all new features. See 
discussion 
https://mail.python.org/pipermail/python-dev/2018-January/151718.html . However 
Travis CI uses Ubuntu 14.04 LTS, which comes with OpenSSL 1.0.1.

To address the problem, CPython has either to compile and install a local copy 
of OpenSSL, move to container-based testing or use a different CI provider with 
more recent infrastructure.

I have created a PR that uses an improved version of my multissl test helper to 
compile and install the latest copy of OpenSSL 1.1.0. The build is cached by 
Travis. I *think* it is necessary to build OpenSSL in master so PRs can use the 
cache. A daily Travis cron job on master should do the trick.

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nosy: christian.heimes
priority: normal
severity: normal
stage: patch review
status: open
title: Travis: Test with OpenSSL 1.1.0
type: enhancement
versions: Python 3.7

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Re: Generating SVG from turtle graphics

[Peter Otten]

Steven D'Aprano wrote:

> I'd like to draw something with turtle, then generate a SVG file from it.
> 
> Is this possible?

If this is a one-off job consider creating Postscript from the underlying 
Canvas:

>>> import turtle
>>> for i in range(12):
... turtle.forward(100)
... turtle.left(150)
... 
>>> turtle.getcanvas().postscript(file="tmp_turtle.ps")
[...]

Then convert to SVG with an external tool. It looks like ghostscript can do
that:

$ gs -dBATCH -dNOPAUSE -sDEVICE=svg -sOutputFile=tmp_turtle.svg tmp_turtle.ps


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Re: Detecting a cycle in a graph

[Steven D'Aprano]

On Sun, 14 Jan 2018 10:30:31 +0200, Frank Millman wrote:

> I can detect a cycle in a path. It is possible for there to be more than
> one gateway in the path. I want to identify the gateway that actually
> triggered the cycle, but I have not figured out a way to do this.

You don't need a gateway to get a cycle. Suppose you have nodes 

A -> B -> C -> D -> B

that's a cycle with no gateways.

If you do have gateways, who is to say which one is to blame? Or even 
that *any* of them is to blame?

A -> (B) -> C -> F -> E
   \
D -> E -> F

Why say that the gateway (B) is to blame for the cycle E -> F -> E?

I'm sure that if you draw some diagrams, you can come up with a scenario 
where a cycle is formed by the action of two gateways, either one on its 
own being harmless. Why blame one rather than the other?

For that matter, why are cycles necessarily harmful? So long as you can 
escape a cycle eventually, that's just a loop with an exit:

A -> B -> C -> (D) -> E -> B
 \
  X

Now the path will loop B -> ... -> E and back to B, until the gateway D 
takes the alternate path and escapes.

The usual way of fixing this sort of thing for systems intended for non-
expert use is to have a (user-configurable?) limit on the number of 
steps, and have the process raise an error once it reaches the limit.


> I scribbled down a pseudo process on the back of an envelope. It has a
> gateway that can cause a cycle.
> 
> Before that, there is a gateway that checks for a 'fast-track'
> indicator. If true, it bypasses the next part of the process and jumps
> to the next stage.
> 
> After that, in the path returning to the previous node, there is another
> gateway that checks a counter. If the boolean check fails three times,
> terminate the process.

What boolean check? You mentioned a counter -- that's normally considered 
to be an integer.


> I can 'visually' identify the gateway that triggers the cycle, but I
> cannot figure out how to determine it 'logically'. My intention is that
> users can create their own processes, and we know that they can
> sometimes create a dog's breakfast, so I cannot rely on it being
> 'obvious'. Maybe there is no logical way of identifying it.
> 
> I am sure you will need more details if you want to assist, but maybe
> there is some literature you can point me to that explains these things
> in more detail.

Try googling for "Halting problem" to learn why you cannot, in general, 
prove that all cycles will eventually terminate. You may be able to 
identify *some* non-terminating graphs, but you cannot determine all of 
them.



-- 
Steve

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[issue17972] inspect module docs omits many functions

[Paul Rudin]

Paul Rudin  added the comment:

Although formatannotation is undocumented, its actually documented as a default 
value for one of the parameters of formatargspec, so it does form part of the 
module's public interface. However formatargspec is deprecated, so it's still 
OK to deprecate formatannotation.

formatannotation is also used as a helper within Parameter, which isn't 
deprecated, but the public interface or docs of Parameter don't mention 
formatannotation, so using _formatannotation instead is fine.

Since I've looked through this and, as far as I can tell, nobody is working on 
it, I'll make the changes and make a PR.

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Detecting a cycle in a graph

[Frank Millman]

Hi all

I am adding a bpm (Business Process Management) module to my accounting app. 
A process is laid out as a flowchart, and is therefore a form of directed 
graph, so I am getting into a bit of graph theory. I got some good ideas 
from this essay - https://www.python.org/doc/essays/graphs/


I need to detect when a 'cycle' occurs - when a path loops back on itself 
and revisits a node previously visited. I have figured out a way to do this, 
but I have a problem.


A cycle occurs as a result of a node with more than one path leading out 
from it. I am following the BPMN spec, and they call these nodes 'gateways', 
so I will use that terminology. A gateway can optionally have a boolean 
condition associated with it, which determines which path is followed. If a 
given path loops back to an earlier node, a cycle is created.


I can detect a cycle in a path. It is possible for there to be more than one 
gateway in the path. I want to identify the gateway that actually triggered 
the cycle, but I have not figured out a way to do this.


I scribbled down a pseudo process on the back of an envelope. It has a 
gateway that can cause a cycle.


Before that, there is a gateway that checks for a 'fast-track' indicator. If 
true, it bypasses the next part of the process and jumps to the next stage.


After that, in the path returning to the previous node, there is another 
gateway that checks a counter. If the boolean check fails three times, 
terminate the process.


I can 'visually' identify the gateway that triggers the cycle, but I cannot 
figure out how to determine it 'logically'. My intention is that users can 
create their own processes, and we know that they can sometimes create a 
dog's breakfast, so I cannot rely on it being 'obvious'. Maybe there is no 
logical way of identifying it.


I am sure you will need more details if you want to assist, but maybe there 
is some literature you can point me to that explains these things in more 
detail.


Thanks

Frank Millman


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