[issue25137] Behavioral change / regression? with nested functools.partial

[Roundup Robot]

Roundup Robot added the comment:

New changeset fa766b6f12b5 by Berker Peksag in branch '3.5':
Issue #25137: Add a note to whatsnew/3.5.rst for nested functools.partial calls
https://hg.python.org/cpython/rev/fa766b6f12b5

New changeset ed694938c61a by Berker Peksag in branch 'default':
Issue #25137: Add a note to whatsnew/3.5.rst for nested functools.partial calls
https://hg.python.org/cpython/rev/ed694938c61a

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[issue25137] Behavioral change / regression? with nested functools.partial

[Berker Peksag]

Berker Peksag added the comment:

Added a note to Doc/whatsnew/3.5.rst.

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stage:  -> resolved

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[issue25137] Behavioral change / regression? with nested functools.partial

[STINNER Victor]

STINNER Victor added the comment:

Tim Graham wrote: "It's fine with me."

Oh, I see that your pull request was merged. I'm now closing the issue.

Anyway, thanks for the bug report. It's always good to have feedback on 
behaviour changes, even when they are legit :-)

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resolution:  -> not a bug
status: open -> closed

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[issue25137] Behavioral change / regression? with nested functools.partial

[STINNER Victor]

STINNER Victor added the comment:

Can we close this issue?

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[issue25137] Behavioral change / regression? with nested functools.partial

[Tim Graham]

Tim Graham added the comment:

It's fine with me.

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[issue25137] Behavioral change / regression? with nested functools.partial

[Markus Holtermann]

Markus Holtermann added the comment:

Interesting thing tough, this optimization is nowhere mentioned in the 3.5 
release notes ;)

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[issue25137] Behavioral change / regression? with nested functools.partial

[STINNER Victor]

STINNER Victor added the comment:

> In my opinion this is a regression since there's no way to turn off the new 
> behavior.

Well, it depends on your point of view :-) On the performance point of view, 
it's much faster to flatten heavily nested partials like:

>>> import functools
>>> f = functools.partial(print, 1)
>>> f = functools.partial(f, 2)
>>> f = functools.partial(f, 3)
>>> f = functools.partial(f, 4)
>>> f = functools.partial(f, 5)
>>> f()
1 2 3 4 5

> This is a behavioral change that causes a test failure in Django because we 
> use nested partials to resolve relationships between models

Can you point me to the code? Why do you need to know the full chain of nested 
partials?

If you need to remember the chain of actions, maybe you can store it manually? 
You can add an attribute to a functools.partial() object. Or you can create a 
subclass of functools.partial.

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[issue25137] Behavioral change / regression? with nested functools.partial

[Antoine Pitrou]

Antoine Pitrou added the comment:

The specific attributes of a partial are not documented, so it is you are 
relying on them. Using partial as a container is also a bit unexpected...

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[issue25137] Behavioral change / regression? with nested functools.partial

[Tim Graham]

Tim Graham added the comment:

We can use an alternate approach in Django, if appropriate: 
https://github.com/django/django/pull/5294

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[issue25137] Behavioral change / regression? with nested functools.partial

[Tim Graham]

Changes by Tim Graham :


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[issue25137] Behavioral change / regression? with nested functools.partial

[Markus Holtermann]

New submission from Markus Holtermann:

Since #7830 nested partials are flattened. This is a behavioral change that 
causes a test failure in Django because we use nested partials to resolve 
relationships between models: 
https://github.com/django/django/pull/4423#issuecomment-138996095

In my opinion this is a regression since there's no way to turn off the new 
behavior.

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components: Library (Lib)
messages: 250814
nosy: MarkusH, belopolsky
priority: normal
severity: normal
status: open
title: Behavioral change / regression? with nested functools.partial
type: behavior
versions: Python 3.5

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[issue25137] Behavioral change / regression? with nested functools.partial

[Raymond Hettinger]

Changes by Raymond Hettinger :


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[issue25137] Behavioral change / regression? with nested functools.partial

[Simon Charette]

Changes by Simon Charette :


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