def find_all(str_:str, key:str):
    """
    Returen all the starting indices of string `key` in string `str_`. 
    
    Example:
    ----------
    >>> find_all("abcaa", 'a')
    [0, 3, 4]
    """
    p, indices = -1, []
    while True:
        p = str_.find(key, p + 1)
        if p < 0: break
        indices.append(p)
    return indices