assert — Intermediate Playground

# Precondition
def binary_search(arr, target):
    assert arr == sorted(arr), "Array must be sorted"
    lo, hi = 0, len(arr) - 1
    while lo <= hi:
        mid = (lo + hi) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            lo = mid + 1
        else:
            hi = mid - 1
    return -1

print(binary_search([1, 3, 5, 7, 9], 5))

# Postcondition
def factorial(n):
    result = 1
    for i in range(2, n + 1):
        result *= i
    assert result > 0, "Factorial must be positive"
    return result

print(factorial(10))

# Type checking assertions
def concat(a, b):
    assert isinstance(a, str) and isinstance(b, str), \
        f"Expected strings, got {type(a).__name__} and {type(b).__name__}"
    return a + b

print(concat("hello", " world"))