By only adding + - * into the string 452874 (in that order), how many way can you get to -18?

452874.py

"""
By only adding + - * into the string 452874 (in that order),
how many way can you get to -18?
"""

N = "452874"
M = -18

OPERATIONS = [None, '+', '-', '*']

for n in range(4**(len(N) - 1)):
    start = 0
    end = 1

    equation = []
    for op in [OPERATIONS[n // 4 ** x % 4] for x in range(len(N) - 1)]:
        if not op:
            end += 1
        else:
            equation.append(N[start:end])
            equation.append(op)
            start = end
            end = start + 1

    equation.append(N[start:])
    e = ' '.join(equation)
    result = eval(e)

    if result == M:
        print(f'{e} = {result}')