Opened 8 years ago
Closed 3 years ago
#16073 closed enhancement (fixed)
Python 3 preparation: The semantic of map() function is changed
Reported by:  wluebbe  Owned by:  

Priority:  major  Milestone:  sageduplicate/invalid/wontfix 
Component:  python3  Keywords:  python3 
Cc:  embray, jdemeyer, fbissey, tscrim, jhpalmieri, vklein  Merged in:  
Authors:  Wilfried Luebbe, André Apitzsch  Reviewers:  
Report Upstream:  N/A  Work issues:  
Branch:  Commit:  
Dependencies:  Stopgaps: 
Description (last modified by )
In Py2 map()
returns a list, while in Py3 map()
returns an iterator (as itertools.imap()
does in Py2).
The tool 2to3 wraps map()
usages with a call to list()
.
An alternative approach is to add from future_builtins import map
and to check the code.
This ticket is tracked as a dependency of metaticket ticket:16052.
Change History (70)
comment:1 Changed 8 years ago by
 Milestone changed from sage6.2 to sage6.3
comment:2 Changed 8 years ago by
 Branch set to u/wluebbe/ticket/16073
 Commit set to 8c8e5dc6783c29333679e28d38ea596f520e3258
comment:3 Changed 8 years ago by
 Commit changed from 8c8e5dc6783c29333679e28d38ea596f520e3258 to b786139346f3c79ef980824ca607b8c0d40f2c22
Branch pushed to git repo; I updated commit sha1. New commits:
b786139  trac #16073: fix an error exposed by the generated code

comment:4 Changed 8 years ago by
The problem was that in one module the standard library function list
had been overwritten. Now all doctests pass.
comment:5 Changed 8 years ago by
The code would now certainly benefit from changing expressions like list(map(...))
into a list comprehension.
This is more pythonic, more readable (especially in the case list(map(lambda ...))
) and it avoids redundant list creation in Python 2. But it's a lot of stuff to check and change ...
comment:6 Changed 8 years ago by
comment:7 Changed 8 years ago by
 Status changed from new to needs_review
comment:8 Changed 8 years ago by
 Status changed from needs_review to needs_work
comment:9 Changed 7 years ago by
 Milestone changed from sage6.3 to sage6.4
comment:10 Changed 7 years ago by
 Branch changed from u/wluebbe/ticket/16073 to public/16073
 Commit changed from b786139346f3c79ef980824ca607b8c0d40f2c22 to 9ebf5fd033b4a6340c817c52ee7b257484cb8ebb
comment:11 Changed 7 years ago by
 Commit changed from 9ebf5fd033b4a6340c817c52ee7b257484cb8ebb to dc803c154c077bb345715e40a662fa14beb38c99
Branch pushed to git repo; I updated commit sha1. New commits:
dc803c1  remove some unnecessary conversions to list

comment:12 Changed 7 years ago by
 Status changed from needs_work to needs_review
comment:13 Changed 7 years ago by
The patch is red.
Either way, shouldn't it be only wrapping some of the uses, rather than all of them?
comment:14 Changed 7 years ago by
 Commit changed from dc803c154c077bb345715e40a662fa14beb38c99 to 6ddc5fc6e2673e0e0edd31e11b1c37350230ca48
Branch pushed to git repo; I updated commit sha1. New commits:
6ddc5fc  Merge remotetracking branch 'origin/develop' into 16073

comment:15 followup: ↓ 17 Changed 7 years ago by
OK, but as I expected there are some questionable things here.
 r = sum ( map( lambda x: x[2], cycle ) ) + r = sum ( [x[2] for x in cycle] )
Wouldn't keeping the old line be better? Summing an iterator should be faster than summing a list which has been constructed merely to be summed.
comment:16 Changed 7 years ago by
 Commit changed from 6ddc5fc6e2673e0e0edd31e11b1c37350230ca48 to 8331e848b1ab06e87ed5114926d941083ff0ae7f
Branch pushed to git repo; I updated commit sha1. New commits:
8331e84  remove more unnecessary conversions to list

comment:17 in reply to: ↑ 15 Changed 7 years ago by
Replying to darij:
OK, but as I expected there are some questionable things here.
 r = sum ( map( lambda x: x[2], cycle ) ) + r = sum ( [x[2] for x in cycle] )Wouldn't keeping the old line be better? Summing an iterator should be faster than summing a list which has been constructed merely to be summed.
You are right.
In this case we should write
r = sum ( (x[2] for x in cycle) )
Feel free to fix it (and others), currently I have no time to check the necessity of list()
wrapping.
comment:18 followup: ↓ 20 Changed 7 years ago by
 return "".join(map(lambda x: self._character_to_code[x], string)) + return "".join([self._character_to_code[x] for x in string])
Wondering if this is a good step forward, given that you can join an iterator to a string:
>>> map(lambda x: x+x, ['a','b','c']) <map object at 0x7fd747ddee10> >>> "blah".join(map(lambda x: x+x, ['a','b','c'])) 'aablahbbblahcc'
(Python 3).
 map(  lambda x: chr(ord(x) + 49),  list(str(num[0]))), + [chr(ord(x) + 49) for x in list(str(num[0]))],
Can't we get rid of the list
?
 a,b,c,d,e,f = map(G,R) + a,b,c,d,e,f = list(map(G,R))
This seems to not be necessary:
>>> a,b,c = iter([1,2,3]) >>> a 1 >>> b 2 >>> c 3
This is unnecessary:
 if all(map(lambda s: s.is_final, state.label())): + if all([s.is_final for s in state.label()]):
If anything then all
definitely works on iterators.
Here is the thing that worries me the most: There are tools for automatic translation of python2 into 3. I am not sure if we should, or are going to, release them on the Sage library; but if we are, I would rather not do any manual work unless we can make sure that it will not interfere with the automated changes. I have a hunches that a wellwritten bot could do better than some of the changes in this patch (for instance, it should be a rule that all(map(...))
can stay as it is rather than being replaced by all(list(map(...)))
), thus leading to better speed, whereas with the changes already done it would not simplify them back to what they should be. This does not speak against edits such as replacing list
variables by list_
and likewise, which are the right thing to do either way. But I would be wary of making changes that possibly complicate the situation without knowing that it will become untangled when the time comes to actually switch to python 3.
comment:19 Changed 7 years ago by
 Commit changed from 8331e848b1ab06e87ed5114926d941083ff0ae7f to 99e57e20ca0f39d11c00a263f82a9de7d4f836ae
Branch pushed to git repo; I updated commit sha1. New commits:
99e57e2  remove furthr unnecessary conversions to list

comment:20 in reply to: ↑ 18 Changed 7 years ago by
Darij thanks. I hopefully made all the changes you suggested.
Replying to darij:
Here is the thing that worries me the most: There are tools for automatic translation of python2 into 3. I am not sure if we should, or are going to, release them on the Sage library; but if we are, I would rather not do any manual work unless we can make sure that it will not interfere with the automated changes. I have a hunches that a wellwritten bot could do better than some of the changes in this patch (for instance, it should be a rule that
all(map(...))
can stay as it is rather than being replaced byall(list(map(...)))
), thus leading to better speed, whereas with the changes already done it would not simplify them back to what they should be. This does not speak against edits such as replacinglist
variables bylist_
and likewise, which are the right thing to do either way. But I would be wary of making changes that possibly complicate the situation without knowing that it will become untangled when the time comes to actually switch to python 3.
These tools don't work well in all cases and usually one can disable special fixes. So manual work won't interfere with automated changes.
The target of these changes is to simplify the switch to python 3 without complicating the situation. :)
comment:21 followup: ↓ 22 Changed 7 years ago by
I got
1 item had failures: 3 of 211 in sage.tests.cmdline.test_executable [210 tests, 3 failures, 29.22 s]  sage t long src/sage/tests/cmdline.py # 3 doctests failed
while there were no failures with plain sage 6.4. I have not yet found the cause.
comment:22 in reply to: ↑ 21 Changed 7 years ago by
Replying to wluebbe:
I got
1 item had failures: 3 of 211 in sage.tests.cmdline.test_executable [210 tests, 3 failures, 29.22 s]  sage t long src/sage/tests/cmdline.py # 3 doctests failedwhile there were no failures with plain sage 6.4. I have not yet found the cause.
I have no problems with cmdline.py
. Results keep the same with and without merging origin/develop
into 16073
.
sage t long src/sage/tests/cmdline.py [210 tests, 32.88 s]  All tests passed!
comment:23 Changed 7 years ago by
Strange! And Volker just released sage6.5.beta0 and automerge failed again ... :(
By the way, back in June I was working to replace map
with list comprehension or generator expressions (mostly). It was not quite complete when I took some time off.
I want to give that approach a fresh start on sage6.5.beta0. I will describe the reasoning tomorrow (or so ...).
comment:24 Changed 7 years ago by
 Commit changed from 99e57e20ca0f39d11c00a263f82a9de7d4f836ae to f47ac2b0aeef8cd6172206c1f6ef36c326dafdc9
Branch pushed to git repo; I updated commit sha1. New commits:
f47ac2b  Merge remotetracking branch 'origin/develop' into 16073

comment:25 Changed 7 years ago by
I uploaded a new branch u/wluebbe/ticket/160732
.
My goal is to replace all map
calls with list comprehension or generator expressions. Currently there are still about 40 list(map(...
in the code (somehow my regexp did not find them :/ ) and a number of map
s in the doctests. So there is still some work to do.
The drawback of wrapping map
with list
is that in Python2 this is redundant.
If a context accepts iterators then in Python2 map
cannot exploit this (as it returns a list). Remapping map
in Python2 on its iterator version itertools.imap
requires extra code.
The current branch does change list comprehensions to generator expressions in all possible cases. I would rather leave this refactoring to a new ticket since there are lots of applicable cases separate from 16073.
I am very much interested in feedback to u/wluebbe/ticket/160732
.
comment:26 Changed 7 years ago by
wluebbe: sorry for the stupid question, but what is the precise difference between the two branches? I cannot tell it from the post.
comment:27 Changed 7 years ago by
The 2 branches (the current public/16073
and u/wluebbe/ticket/160732
) are alternative approaches.
I did not want to be so impolite and just swap the branches :)
And I did not think it is appropriate to open a separate ticket.
comment:28 Changed 7 years ago by
I have added your branch to #15379 (an accidental duplicate ticket I made a year ago) to be able to see it on the trac viewer.
I have to say I have no idea which of your two branches is the better one :/
comment:29 Changed 7 years ago by
My branch gets rid of (mostly) all map(...)
and list(map(...))
calls replacing them with list comprehension or generator expressions.
There are currently a few (about 40) list(map(...))
calls left over (as e.g. in src/sage/graphs/bipartite_graph.py
lines 643ff).
comment:30 Changed 7 years ago by
 Commit changed from f47ac2b0aeef8cd6172206c1f6ef36c326dafdc9 to cf901f987a14edbad31608be8f5cf88b9d099748
Branch pushed to git repo; I updated commit sha1. New commits:
cf901f9  Merge remotetracking branch 'origin/develop' into 16073

comment:32 Changed 7 years ago by
 Commit changed from cf901f987a14edbad31608be8f5cf88b9d099748 to 2c1de15add5af1438c4be1bab3b21accff978e9a
Branch pushed to git repo; I updated commit sha1. New commits:
2c1de15  Merge remotetracking branch 'origin/develop' into 16073

comment:33 Changed 7 years ago by
 Status changed from needs_work to needs_review
comment:34 followup: ↓ 35 Changed 7 years ago by
I find [func(_) for _ in L]
more readable than list(map(func, L))
.
comment:35 in reply to: ↑ 34 Changed 7 years ago by
 Status changed from needs_review to needs_work
Replying to jdemeyer:
I find
[func(_) for _ in L]
more readable thanlist(map(func, L))
.
I will change it.
comment:36 Changed 7 years ago by
 Commit changed from 2c1de15add5af1438c4be1bab3b21accff978e9a to 3ce7033d5eb0377908986f18fa0b2e0681b303af
Branch pushed to git repo; I updated commit sha1. New commits:
3ce7033  make 'list(map(..))' more readable

comment:37 Changed 7 years ago by
 Status changed from needs_work to needs_review
comment:38 Changed 7 years ago by
 Commit changed from 3ce7033d5eb0377908986f18fa0b2e0681b303af to 02ceae747267fe0610ebbcfb126712742cca189d
Branch pushed to git repo; I updated commit sha1. New commits:
02ceae7  revert changes in random_variable.py

comment:39 Changed 7 years ago by
I'm sorry but this is much too boring to review.
comment:40 followup: ↓ 41 Changed 7 years ago by
Are the changes scripted? If so, can you just tell me which script you used to generate them, then I'll review the script instead.
comment:41 in reply to: ↑ 40 ; followup: ↓ 44 Changed 7 years ago by
Replying to jdemeyer:
Are the changes scripted? If so, can you just tell me which script you used to generate them, then I'll review the script instead.
There is no script. But if necessary we can split this ticket.
comment:42 Changed 7 years ago by
 Commit changed from 02ceae747267fe0610ebbcfb126712742cca189d to ce34bea5d35fbba9d7c3d4a642c51cbe87d18e22
Branch pushed to git repo; I updated commit sha1. New commits:
ce34bea  Merge remotetracking branch 'origin/develop' into 16073

comment:43 Changed 7 years ago by
 Milestone changed from sage6.4 to sage6.7
comment:44 in reply to: ↑ 41 Changed 7 years ago by
Replying to aapitzsch:
There is no script.
That actually worries me. If one has to manually review each individual change, that is a lot of changes to review and a lot of potential for mistakes also.
comment:45 Changed 7 years ago by
I still can split this ticket. Would it be sufficient to move the changes in src/sage/combinat/
to a new ticket?
comment:46 Changed 7 years ago by
Well, my preferred solution would be if the majority of the changes would be scripted.
Splitting would help also but maybe 2 pieces are not enough.
comment:47 Changed 7 years ago by
 Commit changed from ce34bea5d35fbba9d7c3d4a642c51cbe87d18e22 to 2916b218b07d9ae20dd030737392df9a1f55419b
Branch pushed to git repo; I updated commit sha1. New commits:
2916b21  revert changes in src/sage/combinat

comment:48 Changed 7 years ago by
 Commit changed from 2916b218b07d9ae20dd030737392df9a1f55419b to 038b9475df4bbda26bdba92b20f2318bbbca5d10
Branch pushed to git repo; I updated commit sha1. New commits:
038b947  revert more changes

comment:49 Changed 7 years ago by
comment:50 Changed 7 years ago by
Can this now be set to closed?
comment:51 Changed 7 years ago by
 Dependencies set to #18472, #18473, #18474, #18531
 Status changed from needs_review to needs_work
No, unfortunately there are still a significant number of map
s in the code base.
@André: Can you please move the branch public/16073
from this ticket into a new, separate ticket. Then I will review the change.  Reason: I will create one (maybe two) extra tickets/changes (this is now #18531) for the leftover map
s that I found during the review of #18473 and #18474. And I would prefer that this tickets only refers to the tickets containing the changes.
comment:52 Changed 7 years ago by
 Commit changed from 038b9475df4bbda26bdba92b20f2318bbbca5d10 to 2df6d8488ef2496ff22cdf45027fc08ab40fe913
Branch pushed to git repo; I updated commit sha1. New commits:
2df6d84  Merge remotetracking branch 'origin/develop' into 16073

comment:53 Changed 7 years ago by
 Branch public/16073 deleted
 Commit 2df6d8488ef2496ff22cdf45027fc08ab40fe913 deleted
 Dependencies changed from #18472, #18473, #18474, #18531 to #18472, #18473, #18474, #18531, #18532
comment:54 Changed 7 years ago by
There are still a lot of map()
call in the code.
But not all occurrences must be removed: there are a number of places where a Py3 map()
iterator leads to the same result as the Py2 map()
.
Here is a long (but incomplete) list:
all(here_is_an_iterable_allowed) any(here_is_an_iterable_allowed) bytearray(here_is_an_iterable_allowed) dict(here_is_an_iterable_of_key_value_pairs_allowed) filter(function, here_is_an_iterable_allowed) frozenset(here_is_an_iterable_allowed) list(here_is_an_iterable_allowed) map(function, here_is_an_iterable_allowed) max(here_is_an_iterable_allowed) min(here_is_an_iterable_allowed) reduce(function, here_is_an_iterable_allowed) set(here_is_an_iterable_allowed) sorted(here_is_an_iterable_allowed) sum(here_is_an_iterable_allowed) tuple(here_is_an_iterable_allowed) zip(here_is_an_iterable_allowed) ''.join(here_is_an_iterable_allowed) a,b,c* = here_is_an_iterable_allowed x[i:j] = here_is_an_iterable_allowed a_dict.update(here_is_an_iterable_of_key_value_pairs_allowed) file.writelines(here_is_an_iterable_allowed) math.fsum(here_is_an_iterable_allowed) and MANY functions in module itertools. for i in here_is_an_iterable_allowed: pass [2*x for x in here_is_an_iterable_allowed] (2*x for x in here_is_an_iterable_allowed)
But if the use of map
includes a lambda
then replacing it with a list comprehension improves the readability!
comment:55 Changed 7 years ago by
 Dependencies changed from #18472, #18473, #18474, #18531, #18532 to #18472, #18473, #18474, #18531, #18532, #18553
 Description modified (diff)
comment:56 Changed 6 years ago by
 Component changed from distribution to python3
 Milestone changed from sage6.7 to sage7.2
comment:57 Changed 6 years ago by
 Dependencies #18472, #18473, #18474, #18531, #18532, #18553 deleted
comment:58 Changed 5 years ago by
comment:59 Changed 5 years ago by
 Milestone changed from sage7.2 to sage8.0
comment:60 Changed 5 years ago by
another step in #23084
comment:61 Changed 5 years ago by
another step in #23130
comment:62 Changed 4 years ago by
next #24382
comment:63 Changed 4 years ago by
next in #24572
comment:64 Changed 4 years ago by
Some more in #25231
comment:65 Changed 4 years ago by
Some more in #25418
comment:66 Changed 3 years ago by
Some more in #25925
comment:67 Changed 3 years ago by
 Cc embray jdemeyer fbissey tscrim jhpalmieri vklein added
 Milestone changed from sage8.0 to sageduplicate/invalid/wontfix
Probably one coud close this one too ? Agreed ?
comment:68 Changed 3 years ago by
 Status changed from needs_work to needs_review
comment:70 Changed 3 years ago by
 Resolution set to fixed
 Status changed from positive_review to closed
This first commit was generated by
2to3
. It has failing doctests! These will be fixed with a separate commit.New commits:
trac #16073: changes generated by "2to3 w f map src/sage"