>>> type(_)
<type 'ellipsis'>
>>> 1 + 1
2
>>> _
2
>>>
what's the usefulness of this _ function?
views:
53answers:
2
+2
A:
It just makes it easier to track intermediate values or to operate on the previously returned value.
>>> [x*x for x in range(5)]
[0, 1, 4, 9, 16]
>>> sum(_) # instead of having to type sum([0,1,4,9,16]) by hand
30
Mark Rushakoff
2010-08-16 16:41:27
so, its not better declare a variable var = [x*x for x in range(5)] sum(var) instead use _?
killown
2010-08-16 16:43:44
i should agree that its usefull when you are using the interpreter as calculator but for test pieces of code i think its a bad pratice.
killown
2010-08-16 16:48:35
The idea is to use it for quick interactive calculations such as this.
Andrew Jaffe
2010-08-16 16:49:28
@killown: The point is that it's interactive. Sure, in thought-out production code, you would use proper variables, but at the REPL, you sometimes call `GetAFoo()` and only once you have received its value are you aware that you need to call its `.Bar()` method. This is the point of the `_` in interactive Python.
Mark Rushakoff
2010-08-16 16:56:02
`_` is *only defined in interactive mode*.
THC4k
2010-08-16 19:16:21
A:
in case you use ipython it's part of ipythons [output caching system] - it just stores the previous output.
edit: oh, it seems to be implemented for the default python interpreter as well.
deif
2010-08-16 16:44:18