Trick Sheet¶

This page contains concise ways to manipulate data in Python that can save you time and code.

Clamp Function¶

A clamp function (clamp(x, minimum, maximum)) lets you constrain the value of an input to a range. If I want to clamp a value x between 1 and 5, the outputs of clamp(x, 1, 5) would look like:

x	clamp(x, 1, 5)
0	1
1	1
4	4
8	5

Writing this kind of function will be helpful in all kinds of places in 6.101. A straightforward way we could write this is by checking whether the value is below the min or above the max and returning the appropriate boundary.

def clamp(x, minimum, maximum):
    """
    Returns x if minimum < x < maximum. Otherwise, returns the appropriate
    boundary.
    """
    if x < minimum:
        return minimum
    if x > maximum:
        return maximum
    return x

However, notice that the built-in min and max functions achieve a one-sided clamp, half the work of our two-sided clamp above.

def clamp_left(x, minimum):
    """
    Returns x if x > minimum. Otherwise, returns minimum.
    """
    return max(x, minimum)

def clamp_right(x, maximum):
    """
    Returns x if x < maximum. Otherwise, returns maximum.
    """
    return min(x, maximum)

It turns out we can combine min and max together to make an elegant clamp function by just nesting one inside the other! I like to structure the clamp with the max function on the outside and the minimum value on the left, so that the clamp looks like the statement minimum < x < maximum.

def clamp(x, minimum, maximum):
    """
    Returns x if minimum < x < maximum. Otherwise, returns the appropriate
    boundary.
    """
    return max(minimum, min(x, maximum))

You don't need to write this as a function if you don't want to! Say we have a list data of variable length. Now, we have a nice way to make sure whatever index we provide can access a valid data point.

def access_data(index):
    """Returns the nearest data point to index."""
    return data[max(0, min(index, len(data)))]

Range Check¶

Sometimes we just want to check if a value is in a range instead of clamping it. A simple way to do this in Python is with a comparison. Operators like < and == wil let you string together three values in a single comparison.

If we want to check whether x is within 1 and 5, we can use 1 <= x <= 5, like so:

>>> x = 10
>>> 1 <= x <= 5
False
>>> x = 3
>>> 1 <= x <= 5
True

Infinity¶

Python has a way to represent infinity, which might be helpful to you to specify values that are invalid or out-of-bounds when looping through a data structure. To use this value, use float('inf').

>>> # Using infinity for players with invalid scores
>>> scores = [15, float('inf'), 20, 3, float('inf'), 30]
>>> min(scores)
3