brackets.py

def checkio(expression):
    brackets = '{}[]()'
    lst = []
    for x in expression:
        if x in brackets:
            lst.append(x)
        if ''.join(lst[-2:]) in ('()', '[]', '{}'):
            lst = lst[:-2]
    return not bool(lst)

#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
    assert checkio("((5+3)*2+1)") == True, "Simple"
    assert checkio("{[(3+1)+2]+}") == True, "Different types"
    assert checkio("(3+{1-1)}") == False, ") is alone inside {}"
    assert checkio("[1+1]+(2*2)-{3/3}") == True, "Different operators"
    assert checkio("(({[(((1)-2)+3)-3]/3}-3)") == False, "One is redundant"
    assert checkio("2+3") == True, "No brackets, no problem"