# [SOLVED] Python – How to check list monotonicity

## Issue

What would be an efficient and pythonic way to check list monotonicity?
i.e. that it has monotonically increasing or decreasing values?

Examples:

``````[0, 1, 2, 3, 3, 4]   # This is a monotonically increasing list
[4.3, 4.2, 4.2, -2]  # This is a monotonically decreasing list
[2, 3, 1]            # This is neither
``````

## Solution

It’s better to avoid ambiguous terms like “increasing” or “decreasing” as it’s not clear if equality is acceptable or not. You should always use either for example “non-increasing” (clearly equality is accepted) or “strictly decreasing” (clearly equality is NOT accepted).

``````def strictly_increasing(L):
return all(x<y for x, y in zip(L, L[1:]))

def strictly_decreasing(L):
return all(x>y for x, y in zip(L, L[1:]))

def non_increasing(L):
return all(x>=y for x, y in zip(L, L[1:]))

def non_decreasing(L):
return all(x<=y for x, y in zip(L, L[1:]))

def monotonic(L):
return non_increasing(L) or non_decreasing(L)
``````