How to limit a number to be within a specified range? (Python)

I want to limit a number to be within a certain range. Currently, I am doing the following:

minN = 1
maxN = 10
n = something() #some return value from a function
n = max(minN, n)
n = min(maxN, n)

This keeps it within minN and maxN, but it doesn’t look very nice. How could I do it better?

PS: FYI, I am using Python 2.6.

Answers:

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Method 1

def clamp(n, minn, maxn):
    return max(min(maxn, n), minn)

or functionally equivalent:

clamp = lambda n, minn, maxn: max(min(maxn, n), minn)

now, you use:

n = clamp(n, 7, 42)

or make it perfectly clear:

n = minn if n < minn else maxn if n > maxn else n

even clearer:

def clamp(n, minn, maxn):
    if n < minn:
        return minn
    elif n > maxn:
        return maxn
    else:
        return n

Method 2

Simply use numpy.clip() (doc):

n = np.clip(n, minN, maxN)

It also works for whole arrays:

my_array = np.clip(my_array, minN, maxN)

Method 3

If you want to be cute, you can do:

n = sorted([minN, n, maxN])[1]

Method 4

Define a class and have a method for setting the value which performs those validations.

Something vaguely like the below:

class BoundedNumber(object):
    def __init__(self, value, min_=1, max_=10):
        self.min_ = min_
        self.max_ = max_
        self.set(value)

    def set(self, newValue):
        self.n = max(self.min_, min(self.max_, newValue))

# usage

bounded = BoundedNumber(something())
bounded.set(someOtherThing())

bounded2 = BoundedNumber(someValue(), min_=8, max_=10)
bounded2.set(5)    # bounded2.n = 8

Method 5

Could you not string together some one-line python conditional statements?

I came across this question when looking for a way to limit pixel values between 0 and 255, and didn’t think that using max() and min() was very readable so wrote the following function:

def clamp(x, minn, maxx):
   return x if x > minm and x < maxx else (minn if x < minn else maxx)

I would be interested to see how someone more experienced than me would find this way of clamping a value. I assume it must be less efficient than using min() and max(), but it may be useful for someone looking for a more readable (to me at least) function.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0