Why is lambda allowed as a key in a dict?

[Daniel Fetchinson]

Python 2.5.1 (r251:54863, Oct 30 2007, 13:45:26)
[GCC 4.1.2 20070925 (Red Hat 4.1.2-33)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

x = { }
x[lambda arg: arg] = 5
x[lambda arg: arg]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: <function <lambda> at 0x2aaaaabaab18>

Is this a case of "we are all adults here"? I should only blame myself
for making an unnamed function a dictionary key or should it be
forbidden? Or am I missing something completely?

Cheers,
Daniel

 

[bearophileHUGS]

See here Daniel Fetchinson:

http://groups.google.com/group/comp.lang.python/browse_thread/thread/a973de8f3562675c

But be quite careful in using that stuff, it has some traps.

Bye,
bearophile

 

[Daniel Fetchinson]

See here Daniel Fetchinson:

http://groups.google.com/group/comp.lang.python/browse_thread/thread/a973de8f3562675c

But be quite careful in using that stuff, it has some traps.

Thanks a lot for all the helpful replies!
Yes, I should name the unnamed lambda function, or better, just use 'def'.

Cheers,
Daniel

 

[Iain King]

Thanks a lot for all the helpful replies!
Yes, I should name the unnamed lambda function, or better, just use 'def'..

Cheers,
Daniel

Sort of tangenitally; is there any real difference between the outcome
of the two following pieces of code?

a = lambda x: x+2

def a(x):
return x+2

Iain

 

[S Arrowsmith]

Sort of tangenitally; is there any real difference between the outcome
of the two following pieces of code?

a = lambda x: x+2

def a(x):
return x+2

a.__name__

As for why that matters, try a(None) and see which gives the more
informative traceback.