Finding way around ABCs (was What for -- for? (was A bug?))

2014-10-30 Thread Rustom Mody 
On Wednesday, October 29, 2014 11:49:27 AM UTC+5:30, Zachary Ware wrote:
 On Wed, Oct 29, 2014 at 1:11 AM, Rustom Mody wrote:
  On Wednesday, October 29, 2014 11:10:06 AM UTC+5:30, Zachary Ware wrote:
  Of course, that's 3 (progressively shorter) loops to get the names of
  the ABCs of a class compared to 1 (fairly short in the first place)
  loop for a map of relationships to all available ABCs, but optimizing
  such a toy as this would just be an exercise in futility :)
 
  Not so.
 
  The charm of introspection is that the introspection
  itself can be introspected.
  For that to be convincing there needs to be a good combo
  of clarity and succinctness.  In particular why not reduce
  the two functions to one?
 
  def get_abc_names(cls):
  return [abc.__name__ for abc in abcs if issubclass(cls,abc)]
 
 Well, it depends on what you actually want, the spec has been a bit fuzzy ;)

Thanks for this much -- its helpful.
Regarding ABCs -- is there a central documentation for them:

What exactly is a sequence or iterable or etc protocol?

This information seems to be strewn all over the place but systematically.
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Re: Finding way around ABCs (was What for -- for? (was A bug?))

2014-10-30 Thread Ian Kelly 
On Thu, Oct 30, 2014 at 11:01 AM, Rustom Mody rustompm...@gmail.com wrote:
 On Wednesday, October 29, 2014 11:49:27 AM UTC+5:30, Zachary Ware wrote:
 On Wed, Oct 29, 2014 at 1:11 AM, Rustom Mody wrote:
  On Wednesday, October 29, 2014 11:10:06 AM UTC+5:30, Zachary Ware wrote:
  Of course, that's 3 (progressively shorter) loops to get the names of
  the ABCs of a class compared to 1 (fairly short in the first place)
  loop for a map of relationships to all available ABCs, but optimizing
  such a toy as this would just be an exercise in futility :)
 
  Not so.
 
  The charm of introspection is that the introspection
  itself can be introspected.
  For that to be convincing there needs to be a good combo
  of clarity and succinctness.  In particular why not reduce
  the two functions to one?
 
  def get_abc_names(cls):
  return [abc.__name__ for abc in abcs if issubclass(cls,abc)]

 Well, it depends on what you actually want, the spec has been a bit fuzzy ;)

 Thanks for this much -- its helpful.
 Regarding ABCs -- is there a central documentation for them:

 What exactly is a sequence or iterable or etc protocol?

 This information seems to be strewn all over the place but systematically.

Maybe the glossary?

https://docs.python.org/3/glossary.html
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Re: Finding way around ABCs (was What for -- for? (was A bug?))

2014-10-30 Thread Ian Kelly 
On Thu, Oct 30, 2014 at 11:09 AM, Ian Kelly ian.g.ke...@gmail.com wrote:
 On Thu, Oct 30, 2014 at 11:01 AM, Rustom Mody rustompm...@gmail.com wrote:
 On Wednesday, October 29, 2014 11:49:27 AM UTC+5:30, Zachary Ware wrote:
 On Wed, Oct 29, 2014 at 1:11 AM, Rustom Mody wrote:
  On Wednesday, October 29, 2014 11:10:06 AM UTC+5:30, Zachary Ware wrote:
  Of course, that's 3 (progressively shorter) loops to get the names of
  the ABCs of a class compared to 1 (fairly short in the first place)
  loop for a map of relationships to all available ABCs, but optimizing
  such a toy as this would just be an exercise in futility :)
 
  Not so.
 
  The charm of introspection is that the introspection
  itself can be introspected.
  For that to be convincing there needs to be a good combo
  of clarity and succinctness.  In particular why not reduce
  the two functions to one?
 
  def get_abc_names(cls):
  return [abc.__name__ for abc in abcs if issubclass(cls,abc)]

 Well, it depends on what you actually want, the spec has been a bit fuzzy ;)

 Thanks for this much -- its helpful.
 Regarding ABCs -- is there a central documentation for them:

 What exactly is a sequence or iterable or etc protocol?

 This information seems to be strewn all over the place but systematically.

 Maybe the glossary?

Also the documentation for the collections.abc and numbers modules:

https://docs.python.org/3/library/collections.abc.html
https://docs.python.org/3/library/numbers.html
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Re: Finding way around ABCs (was What for -- for? (was A bug?))

2014-10-30 Thread Rustom Mody 
On Thursday, October 30, 2014 10:40:42 PM UTC+5:30, Ian wrote:
 On Thu, Oct 30, 2014 at 11:01 AM, Rustom Mody wrote:
  On Wednesday, October 29, 2014 11:49:27 AM UTC+5:30, Zachary Ware wrote:
  On Wed, Oct 29, 2014 at 1:11 AM, Rustom Mody wrote:
   On Wednesday, October 29, 2014 11:10:06 AM UTC+5:30, Zachary Ware wrote:
   Of course, that's 3 (progressively shorter) loops to get the names of
   the ABCs of a class compared to 1 (fairly short in the first place)
   loop for a map of relationships to all available ABCs, but optimizing
   such a toy as this would just be an exercise in futility :)
  
   Not so.
  
   The charm of introspection is that the introspection
   itself can be introspected.
   For that to be convincing there needs to be a good combo
   of clarity and succinctness.  In particular why not reduce
   the two functions to one?
  
   def get_abc_names(cls):
   return [abc.__name__ for abc in abcs if issubclass(cls,abc)]
 
  Well, it depends on what you actually want, the spec has been a bit fuzzy 
  ;)
 
  Thanks for this much -- its helpful.
  Regarding ABCs -- is there a central documentation for them:
 
  What exactly is a sequence or iterable or etc protocol?
 
  This information seems to be strewn all over the place but systematically.
 
 Maybe the glossary?
 
 https://docs.python.org/3/glossary.html

Ummm...

I was looking for something more reference-ish, ie
More prolix for ABCs
And not containing random bits of unconnected data like
- What is CPython
- What is EAFP

Maybe there's something in the bowels of the C(Python)-code?
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Re: What for -- for? (was A bug?)

2014-10-30 Thread Joshua Landau 
On 29 October 2014 03:22, Rustom Mody rustompm...@gmail.com wrote:
 Yesterday I was trying to introduce python to some senior computer scientists.

 Tried showing a comprehension-based dir-walker vs a for-loop based one:

 def dw(p):
if isfile(p):
   return [p]
else:
   return [p] + [c for f in listdir(p) for c in dw(p+'/'+f)]

...

 Comment to me : Well this is neat and compact, but it does not add
 anything fundamental (over usual index based for-loops)

 I tried to say that 'for' over general sequences is quite different
 and significantly more powerful than C/Pascal for over indexes +
 explicit indexing.

If you really want to show the generality of iteration, I suggest you
start with iterators:

def walk(path):
yield path

if isdir(path):
for name in iterdir(path):
for file in walk(path + / + name):
yield file

This is fundementally inexpressable with indexes. It also lends itself
to expressing delegation (eg. yield from walk(path + / + name)).
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Re: What for -- for? (was A bug?)

2014-10-30 Thread Rustom Mody 
On Thursday, October 30, 2014 10:53:13 PM UTC+5:30, Joshua Landau wrote:
 On 29 October 2014 03:22, Rustom Mody  wrote:
  Yesterday I was trying to introduce python to some senior computer 
  scientists.
 
  Tried showing a comprehension-based dir-walker vs a for-loop based one:
 
  def dw(p):
 if isfile(p):
return [p]
 else:
return [p] + [c for f in listdir(p) for c in dw(p+'/'+f)]
 
 ...
 
  Comment to me : Well this is neat and compact, but it does not add
  anything fundamental (over usual index based for-loops)
 
  I tried to say that 'for' over general sequences is quite different
  and significantly more powerful than C/Pascal for over indexes +
  explicit indexing.
 
 If you really want to show the generality of iteration, I suggest you
 start with iterators:
 
 def walk(path):
 yield path
 
 if isdir(path):
 for name in iterdir(path):
 for file in walk(path + / + name):
 yield file

heh!
That was my next version -- almost word-for-word
[Not on that laptop now; will check later]
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Re: What for -- for? (was A bug?)

2014-10-29 Thread Rustom Mody 
On Wednesday, October 29, 2014 11:14:14 AM UTC+5:30, Zachary Ware wrote:
 On Wed, Oct 29, 2014 at 12:27 AM, Ben Finney  wrote:
  Zachary Ware writes:
 
  Of course, Gmail decided to wrap my long line for me. In case it's not
  obvious, that should be a single line.
 
  Right, GMail is a poor choice for composing messages. You might get
  better results installing a proper mail client, and communicating via
  IMAP.
 
 Noted, but it works fine 99% of the time for me.  I'm not really
 interested in trying to get a proper mail client set up on 5 different
 devices and 4 different platforms with settings shared between all
 just to avoid inconvenient line-wrapping (that I can avoid just by
 sticking to 80 column lines in the first place :).

I was going to say the same:
gmail is fine if you remember to press RET 
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Re: What for -- for? (was A bug?)

2014-10-29 Thread Ben Finney 
Zachary Ware zachary.ware+pyl...@gmail.com writes:

 […] just to avoid inconvenient line-wrapping (that I can avoid just by
 sticking to 80 column lines in the first place :).

That is a valid solution. If you have the discipline to stick to it,
congratulations :-)

-- 
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  `\ 'em go, because, man, they're gone.” —Jack Handey |
_o__)  |
Ben Finney

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Re: What for -- for? (was A bug?)

2014-10-29 Thread Rustom Mody 
On Wednesday, October 29, 2014 11:10:06 AM UTC+5:30, Zachary Ware wrote:
 On Wed, Oct 29, 2014 at 12:15 AM, Rustom Mody wrote:
  Maybe nicer to filter out the false's with a filter-false thus??
 
  def ff(d): return [n for n in d if d[n]]
 
 Sure.  Or, combining things:
 
 try:
 from collections import abc
 except ImportError:
 import collections as abc
 from abc import ABCMeta
 
 abcs = [o for o in vars(abc).values() if isinstance(o, ABCMeta)]
 
 def get_abcs(cls):
 return [abc for abc in abcs if issubclass(cls, abc)]
 
 def get_abc_names(cls):
 return [abc.__name__ for abc in get_abcs(cls)]
 
 
 
 Of course, that's 3 (progressively shorter) loops to get the names of
 the ABCs of a class compared to 1 (fairly short in the first place)
 loop for a map of relationships to all available ABCs, but optimizing
 such a toy as this would just be an exercise in futility :)

Not so.

The charm of introspection is that the introspection
itself can be introspected.
For that to be convincing there needs to be a good combo
of clarity and succinctness.  In particular why not reduce
the two functions to one?

def get_abc_names(cls):
return [abc.__name__ for abc in abcs if issubclass(cls,abc)]
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Re: What for -- for? (was A bug?)

2014-10-29 Thread Zachary Ware 
On Wed, Oct 29, 2014 at 1:11 AM, Rustom Mody rustompm...@gmail.com wrote:
 On Wednesday, October 29, 2014 11:10:06 AM UTC+5:30, Zachary Ware wrote:
 Of course, that's 3 (progressively shorter) loops to get the names of
 the ABCs of a class compared to 1 (fairly short in the first place)
 loop for a map of relationships to all available ABCs, but optimizing
 such a toy as this would just be an exercise in futility :)

 Not so.

 The charm of introspection is that the introspection
 itself can be introspected.
 For that to be convincing there needs to be a good combo
 of clarity and succinctness.  In particular why not reduce
 the two functions to one?

 def get_abc_names(cls):
 return [abc.__name__ for abc in abcs if issubclass(cls,abc)]

Well, it depends on what you actually want, the spec has been a bit fuzzy ;)

-- 
Zach
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Re: What for -- for? (was A bug?)

2014-10-29 Thread Terry Reedy 

On 10/29/2014 1:42 AM, Zachary Ware wrote:

to avoid inconvenient line-wrapping (that I can avoid just by
sticking to 80 column lines in the first place:).


Try perhaps 65 for email.

def get_abc_map(cls):
return {n: issubclass(cls, getattr(abc, n))
for n in dir(abc) if n[0].isupper()}

is less than 55 and should not get linewrapped on any sensible sender or 
reader.


--
Terry Jan Reedy

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What for -- for? (was A bug?)

2014-10-28 Thread Rustom Mody 
On Wednesday, October 29, 2014 7:47:47 AM UTC+5:30, Denis McMahon wrote:
 On Tue, 28 Oct 2014 01:29:28 +, Joshua Landau wrote:
 
  On 28 October 2014 00:36, Denis McMahon wrote:
 
  d = [[list(range(1,13))[i*3+j] for j in range(3)] for i in range(4)]
  
  A quick note. Ranges (even 2.7's xrange) are all indexable. The cast to
  a list isn't needed.
 
 Until you apply Chris' slicing trick, and then:
 
  [list(range(1,13))[i*3:i*3+3] for i in range(4)]
 [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]
  [range(1,13)[i*3:i*3+3] for i in range(4)]
 [range(1, 4), range(4, 7), range(7, 10), range(10, 13)]
  
 
 Depends how important it is that you get a list and not a range object ;)

Heh!

Strange that you say this in this context!
Yesterday I was trying to introduce python to some senior computer scientists.

Tried showing a comprehension-based dir-walker vs a for-loop based one:

def dw(p):
   if isfile(p):
  return [p]
   else:
  return [p] + [c for f in listdir(p) for c in dw(p+'/'+f)]


def dw(p):
if isfile(p):
return [p]
else:
ls = [p]
for f in listdir(p):
ls = ls+[f]
for c in dw(p+'/'+f):
ls = ls+[c]
return ls

Comment to me : Well this is neat and compact, but it does not add 
anything fundamental (over usual index based for-loops)

I tried to say that 'for' over general sequences is quite different
and significantly more powerful than C/Pascal for over indexes +
explicit indexing.

In particular the fact that in python-3:
 range(1,10)
range(1, 10)

and not like python2's

 range(1,10)
[1, 2, 3, 4, 5, 6, 7, 8, 9]

seemed to convincingly show that python's range is just 
'notional' like Pascal's subrange types and not an actual sequence.

That
 range(10)+range(10)

works in python 2 but not 3

does not help my case at all!

I'd be interested in thoughts on this -- is a range a 'real' or a 'notional'
sequence?

Related point: A range is a sequence
How to prove this introspectively?

ie if I do:

 type([]).__mro__
(class 'list', class 'object')
 type(range(10)).__mro__
(class 'range', class 'object')
 

How to see that list and range are both sequences?
Or more generally how to to introspectively discover (ie not by reading docs!!)
the abstract base classes -- eg sequence, iterable etc -- for an arbitrary
object?
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Zachary Ware 
On Tue, Oct 28, 2014 at 10:22 PM, Rustom Mody rustompm...@gmail.com wrote:
 How to see that list and range are both sequences?
 Or more generally how to to introspectively discover (ie not by reading 
 docs!!)
 the abstract base classes -- eg sequence, iterable etc -- for an arbitrary
 object?

# Python 2/3 compatible.  Combine with pprint for nice interactive output
try:
from collections import abc
except ImportError:
import collections as abc

def get_abc_map(cls):
   return {n: issubclass(cls, getattr(abc, n)) for n in dir(abc) if
n[0].isupper()}

-- 
Zach
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Zachary Ware 
On Tue, Oct 28, 2014 at 11:16 PM, Zachary Ware
zachary.ware+pyl...@gmail.com wrote:
 def get_abc_map(cls):
return {n: issubclass(cls, getattr(abc, n)) for n in dir(abc) if
 n[0].isupper()}

Of course, Gmail decided to wrap my long line for me.  In case it's
not obvious, that should be a single line.

-- 
Zach
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Rustom Mody 
On Wednesday, October 29, 2014 9:53:46 AM UTC+5:30, Zachary Ware wrote:
 On Tue, Oct 28, 2014 at 11:16 PM, Zachary Ware wrote:
  def get_abc_map(cls):
 return {n: issubclass(cls, getattr(abc, n)) for n in dir(abc) if
  n[0].isupper()}
 
 Of course, Gmail decided to wrap my long line for me.  In case it's
 not obvious, that should be a single line.

Thanks

Wrapping -- no problem.
But the isupper looks like black-magic :-)

And removing the ' ... if n[0].isupper()'
breaks the code
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Zachary Ware 
On Tue, Oct 28, 2014 at 11:40 PM, Rustom Mody rustompm...@gmail.com wrote:
 On Wednesday, October 29, 2014 9:53:46 AM UTC+5:30, Zachary Ware wrote:
 On Tue, Oct 28, 2014 at 11:16 PM, Zachary Ware wrote:
  def get_abc_map(cls):
 return {n: issubclass(cls, getattr(abc, n)) for n in dir(abc) if
  n[0].isupper()}

 Of course, Gmail decided to wrap my long line for me.  In case it's
 not obvious, that should be a single line.

 Thanks

 Wrapping -- no problem.
 But the isupper looks like black-magic :-)

 And removing the ' ... if n[0].isupper()'
 breaks the code

It's a terrible hack for 2/3 compatibility; in 3 I'd do if not
n.startswith('__') since the Python 3 collections.abc module only
contains ABCs (and the standard dunder names).  Python 2 has all the
ABCs mixed into the toplevel collections namespace with some other
non-ABCs, but it happens that all the ABCs are capitalized, while the
non-ABCs are not.  The ABCs are imported into collections from
_abcoll, but _abcoll also some uncapitalized non-ABCs as well.

For somewhat greyer magic, do 'from abc import ABCMeta' and filter the
collections.abc namespace with isinstance(obj, ABCMeta).  I just
used the above because it's short and sweet and keeps the name handy
:)

-- 
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Rustom Mody 
On Wednesday, October 29, 2014 10:29:48 AM UTC+5:30, Zachary Ware wrote:
 On Tue, Oct 28, 2014 at 11:40 PM, Rustom Mody  wrote:
  On Wednesday, October 29, 2014 9:53:46 AM UTC+5:30, Zachary Ware wrote:
  On Tue, Oct 28, 2014 at 11:16 PM, Zachary Ware wrote:
   def get_abc_map(cls):
  return {n: issubclass(cls, getattr(abc, n)) for n in dir(abc) if
   n[0].isupper()}
 
  Of course, Gmail decided to wrap my long line for me.  In case it's
  not obvious, that should be a single line.
 
  Thanks
 
  Wrapping -- no problem.
  But the isupper looks like black-magic :-)
 
  And removing the ' ... if n[0].isupper()'
  breaks the code
 
 It's a terrible hack for 2/3 compatibility; in 3 I'd do if not
 n.startswith('__') since the Python 3 collections.abc module only
 contains ABCs (and the standard dunder names).  Python 2 has all the
 ABCs mixed into the toplevel collections namespace with some other
 non-ABCs, but it happens that all the ABCs are capitalized, while the
 non-ABCs are not.  The ABCs are imported into collections from
 _abcoll, but _abcoll also some uncapitalized non-ABCs as well.
 
 For somewhat greyer magic, do 'from abc import ABCMeta' and filter the
 collections.abc namespace with isinstance(obj, ABCMeta).  I just
 used the above because it's short and sweet and keeps the name handy
 :)

Ha!
Thanks

Maybe nicer to filter out the false's with a filter-false thus??

def ff(d): return [n for n in d if d[n]]
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Ben Finney 
Zachary Ware zachary.ware+pyl...@gmail.com writes:

 Of course, Gmail decided to wrap my long line for me. In case it's not
 obvious, that should be a single line.

Right, GMail is a poor choice for composing messages. You might get
better results installing a proper mail client, and communicating via
IMAP.

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  `\  so, Brain, but how will we get three pink flamingos into one |
_o__) pair of Capri pants?” —_Pinky and The Brain_ |
Ben Finney

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Re: What for -- for? (was A bug?)

2014-10-28 Thread Zachary Ware 
On Wed, Oct 29, 2014 at 12:15 AM, Rustom Mody rustompm...@gmail.com wrote:
 Maybe nicer to filter out the false's with a filter-false thus??

 def ff(d): return [n for n in d if d[n]]

Sure.  Or, combining things:

try:
from collections import abc
except ImportError:
import collections as abc
from abc import ABCMeta

abcs = [o for o in vars(abc).values() if isinstance(o, ABCMeta)]

def get_abcs(cls):
return [abc for abc in abcs if issubclass(cls, abc)]

def get_abc_names(cls):
return [abc.__name__ for abc in get_abcs(cls)]



Of course, that's 3 (progressively shorter) loops to get the names of
the ABCs of a class compared to 1 (fairly short in the first place)
loop for a map of relationships to all available ABCs, but optimizing
such a toy as this would just be an exercise in futility :)

-- 
Zach
-- 
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Re: What for -- for? (was A bug?)

2014-10-28 Thread Zachary Ware 
On Wed, Oct 29, 2014 at 12:27 AM, Ben Finney ben+pyt...@benfinney.id.au wrote:
 Zachary Ware zachary.ware+pyl...@gmail.com writes:

 Of course, Gmail decided to wrap my long line for me. In case it's not
 obvious, that should be a single line.

 Right, GMail is a poor choice for composing messages. You might get
 better results installing a proper mail client, and communicating via
 IMAP.

Noted, but it works fine 99% of the time for me.  I'm not really
interested in trying to get a proper mail client set up on 5 different
devices and 4 different platforms with settings shared between all
just to avoid inconvenient line-wrapping (that I can avoid just by
sticking to 80 column lines in the first place :).

Although if you have a suggestion for that kind of setup, I'm all ears.

-- 
Zach
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