[issue27738] odd behavior in creating list of lambda expressions

[John Sahr]

John Sahr added the comment:

I eventually figured that out that source of the problem;

thanks for the coding fix; that's useful to know.

-John

On Thu, Aug 11, 2016 at 8:17 AM, Emanuel Barry 
wrote:

>
> Emanuel Barry added the comment:
>
> This is due to the fact that Python evaluates the variable 'n' when the
> function is called, not when it is created. As such, the variable holds the
> latest value for all functions, and they exhibit identical behaviour.
>
> Workaround:
>
> ...
> f = lambda x, n=n: sin(n*x)
> ...
>
> And this should work as you expect. More information is available at
> https://docs.python.org/3/faq/programming.html#why-do-
> lambdas-defined-in-a-loop-with-different-values-all-return-the-same-result
>
> --
> nosy: +ebarry
> resolution:  -> not a bug
> stage:  -> resolved
> status: open -> closed
> versions:  -Python 2.7
>
> ___
> Python tracker 
> <http://bugs.python.org/issue27738>
> ___
>

--

___
Python tracker 
<http://bugs.python.org/issue27738>
___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue27738] odd behavior in creating list of lambda expressions

[John Sahr]

New submission from John Sahr:

The following produces unexpected behavior.
I think that it should produce a list of six different lambda expressions,
but after creation, all six lambda expressions produce the same output.
It's possible that I'm missing something about Python.

# begin example ###
from math import *

mm = []

for n in range(6):
f = lambda x: sin(n*x)
print f, f(1.0)
mm.append(f)

print '***'

for m in mm:
print m, m(1.0)
## end example 

--
messages: 272454
nosy: John Sahr
priority: normal
severity: normal
status: open
title: odd behavior in creating list of lambda expressions
type: behavior
versions: Python 2.7

___
Python tracker 
<http://bugs.python.org/issue27738>
___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com