Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #89641

Re: mixing set and list operations

Show key headers only | View raw

[Multipart message — attachments visible in raw view] - view raw

Hi Tim,

On 04/30/2015 10:07 AM, Tim wrote:
> I noticed this today, using Python2.7 or 3.4, and wondered if it is implementation dependent:
> 
> You can use 'extend' to add set elements to a list and use 'update' to add list elements to a set.
> 
>>>> m = ['one', 'two']
>>>> p = set(['three', 'four'])
>>>> m.extend(p)
>>>> m
> ['one', 'two', 'four', 'three']
> 
>>>> m = ['one', 'two']
>>>> p = set(['three', 'four'])
>>>> p.update(m)
>>>> p
> set(['four', 'three', 'two', 'one'])
> 
> 
> Useful if you don't care about ordering. Not sure if it's dangerous.

I don't think this is surprising, nor implementation dependent, nor
dangerous. Lists have an `extend()` method, sets have an `update()`
method. Both of these methods take any iterable as input, they don't
needlessly constrain the input to be of the same type as the base
object. That's the Pythonic way to do it; I'd be surprised if it didn't
work.

Carl

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

mixing set and list operations Tim <jtim.arnold@gmail.com> - 2015-04-30 09:07 -0700
  Re: mixing set and list operations Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-30 10:21 -0600
  Re: mixing set and list operations Carl Meyer <carl@oddbird.net> - 2015-04-30 10:16 -0600
  Re: mixing set and list operations Ben Finney <ben+python@benfinney.id.au> - 2015-05-01 03:04 +1000
    Re: mixing set and list operations Tim <jtim.arnold@gmail.com> - 2015-04-30 10:47 -0700

csiph-web