Basic bash brace expansion exercise

brace_expand.py

def brace_expand(expr):
    expansions = []
    for block in expr.split('{'):
        if '}' in block:
            expansion, remainder = block.split('}')
            expanded = []
            for piece in expansions:
                for component in expansion.split(','):
                    expanded.append("".join((piece, component, remainder)))
            expansions = expanded
        else:
            expansions.append(block)

    return " ".join(expansions)

tests.py

from brace_expand import brace_expand


def test_simple():
    assert brace_expand("{ab,c}a") == "aba ca"


def test_multiple():
    assert brace_expand("{ab,c,d,ef}a") == "aba ca da efa"


def test_with_prefix_and_suffix():
    assert brace_expand("a{ab,c}a") == "aaba aca"


def test_double():
    assert brace_expand("{ab,c}{d,e}") == "abd abe cd ce"


def test_double_with_middle():
    assert brace_expand("{ab,c}ff{d,e}") == "abffd abffe cffd cffe"


def test_double_with_prefix_and_suffix():
    assert brace_expand("f{ab,c}{d,e}f") == "fabdf fabef fcdf fcef"


def test_no_expansion():
    assert brace_expand("d,e") == "d,e"