Why?

I recently found that PHP break accepts an optional numeric argument which tells it how many nested enclosing structures are to be broken out of.

I thought it would be nice to have similar functionality in Python.

We all have written code like following at least once

result = []
for row in grid:
    valid = False
    for col in row:
        if some_method(row, col, result):
            valid = True
            break
    if valid:
        break

Wouldn't it be nice to just break both loops with a single statement?

Do you need it?

Kinda, but not really. There are many ways to deal with it when you want to exit all the enclosing loops. But breakn is useful when you need to exit only a few loops amongst many nested loops.

# refactor the logic inside a function and return
def foo():
    result = []
    for row in range(num_rows):
        for col in range(num_cols):
            if some_method(row, col, result):
                return result

# flatten the loops if possible, into a single loop
from itertools import product

result = []
for row, col in product(range(num_rows), range(num_cols)):
    if some_method(row, col, result):
        break

Usage

from breakn.breaker import breaker


@breaker
def find_n_submatrices(matrix, n, N, M, K, T):
    """
    find top left corner of first 'n' K x K submatrices where all cells are >= T
    """
    results = []
    for i in range(N - K + 1):
        for j in range(M - K + 1):
            valid = True
            for x in range(K):
                for y in range(K):
                    if matrix[i + x][j + y] < T:
                        valid = False
                        breakn(2)
            if valid:
                results.append((i, j))
            if len(results) == n:
                breakn(2)
    return results


matrix = [
    [6, 7, 5, 8, 9],
    [5, 4, 6, 7, 8],
    [7, 8, 5, 6, 7],
    [6, 7, 8, 9, 4]
]
N = 4
M = 5
K = 2
T = 5
n = 4
print(find_n_submatrices(matrix, n, N, M, K, T))  # prints [(0, 2), (0, 3), (1, 2), (1, 3)]

Limitations

• Only works with for loops
• Breaks for-else

PS - I just wrote this for fun, so there might be many breaking cases.