What is the best way to return a boolean when a negative value exists in a list?

Question

I have the following funciton telling us that a series has at least one negative value:

def has_negative(series):
    v=False
    for i in range(len(series)):
        if series[i]<0:
            v=True
            break
    return v

When we use this function on an example we get :

y=[1,2,3,4,5,6,7,8,9]
z=[1,-2,3,4,5,6,7,8,9]

print(has_negative(y))
print(has_negative(y))

Output:

>>> False
>>> True

The function seems to work well, although I want to make it shorter, any suggestion from your side will be appreciated

Asked By: Khaled DELLAL

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Source

Answer 1

There are several improvements you can make:

def has_negative(series):
    for i in series:
        if i < 0:
            return True
    return False

or it can be contracted into one line like this:

print(bool([i for i in z if i<0]))

Answered By: quamrana

Answer 2

You can utilise the built-in any function as follows:

def has_negative(lst):
    return any(e < 0 for e in lst)

print(has_negative([1,2,3,4,5,6,7,8,9]))
print(has_negative([1,-2,3,4,5,6,7,8,9]))

Output:

False
True

EDIT:

Did some timing tests based around this and other suggested answers. Whilst this is concise and functionally correct, it doesn’t perform well. Keep it simple and use @quamrana’s first suggestion – it’s much faster

Answered By: Cobra

Answer 3

You can sort the list and get the first element, check if it’s a negative. With this approach you don’t have to iterate over the array:

sorted(series)[0] < 0

Answered By: iurii_n

Answer 4

To add:

To keep it clean and short, you could also use a list comprehension within a lambda function as follows:

has_negative = lambda series: True if [series for x in series if x < 0] else False

z = [1,-2,3,4,5,6,7,8,9]

has_negative(z)

Output:

>>> True

Answered By: Marble_gold

What is the best way to return a boolean when a negative value exists in a list?

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