_ is just a variable like any other, but by convention it means
that you don’t intend to use that value, just declare and forget it.
[OrderedSet() for _ in xrange(n)]
builds a list of n empty ordered sets. _ is the index, but is unused; _ is commonly used as required, but unused, variable name (not only in Python).
This is just a tricky Python idiom because there is no built-in syntax to do this.
It’s not uncommon to see this in other languages (where _ is a valid identifier). _ often
means a variable one’s not interested in the value of, but which is
needed for syntactic reasons.
Note that _(...) as a macro call has another conventional meaning, which
comes from gettext, where one uses _("string literal") to indicate a
string that needs localization.
A thread to read from ActivesState
I can not say about any problems, Python doesn’t use it internally, it’s just a variable, it is us who have to be careful.
Regarding the syntax of * and **: The names *args and **kwargs are only by convention, but there’s no need not to use them.
def my_callbacK_handler(a, b, *_):
...
So what I understand if I see this function in your code by _ idiom, that this function only uses a and b arguments in its working and will ignore others.
As you state: “*_ to express no interest in any further arguments”.