[issue15987] Provide a way to compare AST nodes for equality recursively

[Batuhan Taskaya]

Change by Batuhan Taskaya :


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pull_request: https://github.com/python/cpython/pull/19211

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Batuhan Taskaya]

Batuhan Taskaya  added the comment:

The solution to hashing used in PR 14970 was just using the default hashing 
function which is kind of a workaround to the real problem. I now concur with 
your comments. Will try to draft out an `ast.compare` function.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I am not sure that implementing a rich comparison of AST nodes is the right 
way. There are too much options (compare attributes or not, compare recursively 
or not, compare types or not) and __eq__ does not support options. In addition, 
it requires implementing compatible __hash__, but how do you implement a hash 
of mutable object? In addition, recursive comparison can introduce a regression 
in existing code -- instead of fast returning False the comparison will spent a 
nontrivial amount of time.

If implement a comparison of AST nodes, it should be a separate function which 
support multiple options. Would be nice also to have examples where this 
feature can be used before implementing it.

See also issue37792.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Brett Cannon]

Change by Brett Cannon :


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[issue15987] Provide a way to compare AST nodes for equality recursively

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

> If consensus has been reached on this, I am willing to do the work.

It looks like there is already an active PR 
https://github.com/python/cpython/pull/14970, there are some non-implemented 
comments from a core review.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[STINNER Victor]

Change by STINNER Victor :


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[issue15987] Provide a way to compare AST nodes for equality recursively

[Philip Dye]

Philip Dye  added the comment:

If consensus has been reached on this, I am willing to do the work.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Flavian Hautbois]

Change by Flavian Hautbois :


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keywords: +patch
pull_requests: +14739
stage: resolved -> patch review
pull_request: https://github.com/python/cpython/pull/14970

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

Btw, I am +1 on this feature (preferably with an option to check line, column, 
end line, and end column). I always wanted this, but never had time to actually 
implement this.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[STINNER Victor]

Change by STINNER Victor :


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versions: +Python 3.8 -Python 3.4

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[issue15987] Provide a way to compare AST nodes for equality recursively

[STINNER Victor]

STINNER Victor  added the comment:

Please don't close an issue too fast.

The PR 1368 is still open and contains valuable code.

Moreover, I don't see anyone here saying that the feature is a bad idea. The 
feature has not been implemented, so the issue should remain open, even if PR 
1368 is outdated.

> ...issue... targets Python 3.4

Well, it's just that the issue has been created a long time ago, but the 
feature request remain value for Python 3.8.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[anthony shaw]

anthony shaw  added the comment:

Closing issue, PR branch has since been removed and targets Python 3.4

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[issue15987] Provide a way to compare AST nodes for equality recursively

[anthony shaw]

anthony shaw  added the comment:

This discussion is inconclusive and targets an old version of CPython, can this 
issue be closed?

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Louie Lu]

Changes by Louie Lu :


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[issue15987] Provide a way to compare AST nodes for equality recursively

[Louie Lu]

Louie Lu added the comment:

Update to AST base type richcompare.

the unittest finished time was better than python version:

Ran 7 tests in 0.278s

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Louie Lu]

Louie Lu added the comment:

Provide a recursive way to compare AST nodes, it will compare with fields, but 
no attributes.


The performance compare with ast.dump methods in unittest


# Recursive compare
./python -m unittest test.test_ast.ASTCompareTest
..
--
Ran 6 tests in 0.669s

OK

# ast.dump compare
./python -m unittest test.test_ast.ASTCompareTest
..
--
Ran 6 tests in 2.192s

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Louie Lu]

Changes by Louie Lu :


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[issue15987] Provide a way to compare AST nodes for equality recursively

[Louie Lu]

Louie Lu added the comment:

If we only need a binary True/False result, could we just return a compare of 
dump(a) == dump(b)?

This can also add the include_attributes flags for need.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Brett Cannon]

Brett Cannon added the comment:

I have a use for this as well, but w/o the lineno/col_offset comparison and all 
I need is a True/False result.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Brett Cannon]

Brett Cannon added the comment:

IOW I think a function that uses ast.walk() and has flags for specifying 
whether _attributes should also be checked and then uses a class check and then 
uses _fields to do all other checking.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Benjamin Peterson]

Benjamin Peterson added the comment:

Yes, though some things like what to return if one has an entire subtree that 
the other doesn't have will have to be worked out.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Brett Cannon]

Changes by Brett Cannon br...@python.org:


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[issue15987] Provide a way to compare AST nodes for equality recursively

[Benjamin Peterson]

Benjamin Peterson added the comment:

This is a reasonable request. Should comparison include lineno/col_offset or 
not? If you implement, __eq__, you should also implement __hash__. Maybe, it 
would be best to start with a helper comparison function in the ast module.

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Julian Berman]

Julian Berman added the comment:

I'd say yes (to both lineno/col_offset). And yeah that sounds like what I had 
in mind (a helper function).

If I'm specific for a moment about implementation, perhaps something like 
`ast.diff`, which yielded tuples of differing nodes (in say, breadth first 
order down the tree) from two given nodes, and took args for configuration, 
compare_lineno and compare_col_offset (both defaulted to True), and then __eq__ 
was just `next(ast.diff(self, other, compare_lineno=True, 
compare_col_offset=True), None) is None`.

Sound good to you?

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Terry J. Reedy]

Changes by Terry J. Reedy tjre...@udel.edu:


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stage:  - test needed
versions:  -Python 3.3

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[issue15987] Provide a way to compare AST nodes for equality recursively

[Julian Berman]

New submission from Julian Berman:

As is, as far as I can tell, there's no way to easily compare two AST nodes to 
see if they have the same children and same fields (recursively).

I'm writing some unit tests for a NodeTransformers, so I've settled for 
comparing `ast.dump()`s of each, which is kind of dirty, but 1) works and 2) 
produces reasonable failure messages. (As a side note of what else I've tried, 
comparing, say, a list of the `iter_child_nodes` is not a good alternative, 
since the tests I'm writing are making assertions that a given node was not 
modified, which means they deepcopy the node and then want to assert that the 
transformed node is unchanged.)

I don't know the global implications of changing ast.AST.__eq__ to know if 
that's feasible (hopefully someone will comment on that), but if it isn't, 
another provided way would be nice.

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components: Library (Lib)
messages: 170826
nosy: Julian
priority: normal
severity: normal
status: open
title: Provide a way to compare AST nodes for equality recursively
type: enhancement
versions: Python 3.3, Python 3.4

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[issue15987] Provide a way to compare AST nodes for equality recursively

[STINNER Victor]

Changes by STINNER Victor victor.stin...@gmail.com:


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