Safe Max or Min (Max/Min Monoid) #python

safe_max_safe_min.py

# sometimes you're streaming through values in a for loop
# and you need to maintain a running max or min
# it's not elegant to get the head separately from the loop
# to solve this, we need a sentinel value to fold the max/min
# operation over the stream
# also known as the "identity element" of the max/min monoid

# in real world use cases, this could be a CSV stream
stream = (i for i in [1, 2, 3])

# start with the identity element/sentinel value
# of negative infinity for max
# and positive infinity for min
max_value = float('-inf')
min_value = float('inf')

for next_value in stream:
    max_value = max(max_value, next_value)
    min_value = min(min_value, next_value)

# in some cases you want to use None as a sentinel value
# you can use these functions
# but I don't think it will be as efficient!


def max_safe(max_value, next_value):
    if next_value is None:
        return max_value
    elif max_value is None:
        return next_value
    else:
        return max(max_value, next_value)


def min_safe(min_value, next_value):
    if next_value is None:
        return min_value
    elif min_value is None:
        return next_value
    else:
        return min(min_value, next_value)