When is "_." used in python

Question

Sometimes I have seen people using the expression _. in python code. For example,

_.objectName = 23

Can someone help me out what exactly does "_." mean? Can someone give me more examples of this type with explanation?

By code, do you mean you've seen it on an interpreter, a Read Eval Print Loop (`>>> `)? — Russia Must Remove Putin, Mar 04 '14 at 22:48

score 6 · Answer 1 · answered Mar 04 '14 at 22:33

6

_ is a valid variable name in python (as well as most other languages.) It's conventionally used to store throw-away values you don't care about. Using the variable, as in your example, is bad form.

answered Mar 04 '14 at 22:33

Swiss

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If it's a throwaway value, why is a method being called on it? – Russia Must Remove Putin Mar 04 '14 at 22:37
2

@AaronHall that is why he said it was bad form – cmd Mar 04 '14 at 22:40
@cmd See another common usage in my answer, I think that would be much more likely. – Russia Must Remove Putin Mar 04 '14 at 22:41
@AaronHall which is not valid because he said it was in python code. – cmd Mar 04 '14 at 22:42
So on a REPL, it's no longer code? I doubt the OP had that intention. – Russia Must Remove Putin Mar 04 '14 at 22:45

Russia Must Remove Putin · Answer 2 · 2014-03-04T22:47:23.270

In your case, it's likely that you've seen that in an interpreter, where it typically aliases the last returned value.

For example:

>>> foo = 'bar'
>>> foo
'bar'
>>> _
'bar'
>>> _.upper()
'BAR'

It is sometimes used as a throwaway, e.g. make a list of ten items unrelated to range:

['foo' for _ in range(10)]

But in this case, there would be no reason to call a method or reference an attribute on it, so I think the usage you've seen is more likely attributed to interpreter use. If you see this in scripts, that would be bad form, but I've rarely seen that.

When is "_." used in python

2 Answers2