I am using python to learn about data science. Everything is fine but recently I found below code in a book. I can't understand for what purpose '_' is being used.
def raw_majority_vote(labels):
votes = Counter(labels)
winner, _ = votes.most_common(1)[0]
return winner
In this piece of code you posted, the _ is a variable name.
You can assign values to _.
I.e.:
>>> _ = "test"
>>> print _
Output:
test
If you take a look at Counter.most_common() docs, you'll see this message:
Return a list of the n most common elements and their counts from the most common to the least. If n is omitted or None, most_common() returns all elements in the counter. Elements with equal counts are ordered arbitrarily:
>>> Counter('abracadabra').most_common(3) [('a', 5), ('r', 2), ('b', 2)]
So, in your code, winner, _ = votes.most_common(1)[0]
The variable winner gets the first value of the first tuple contained in this most_common list.
And the variable, _, gets the second value of the first tuple in this list.
In this case:
winner = 'a'
_ = 5
It's a throwaway variable. Whatever votes.most_common(1)[0] is can be unpacked to two values and the writer of that script is only interested in the first value.
Usually it is used when you don't care about returned variable and you want to discard it but still prevent any ValueErrors.
