Python - recursion - phone keypad text combinations (Stackoverflow)

# date: 2026.02.27

# [recursion - Recursive keypad combination not generating correct result in Python - Stack Overflow](https://stackoverflow.com/questions/79897905/recursive-keypad-combination-not-generating-correct-result-in-python)


d = {
    "1": "abc",
    "2": "def",
    "3": "ghi",
    "4": "jkl",
    "5": "mnop",
    "6": "qrst",
    "7": "uv",
    "8": "wxyz",
    "9": ".;",
    "0": "?!",
}


def keypad_combination(d, s, result, indx):
    # print(f"[DEBUG] {indx = }, {result =}")

    if indx == len(s):
        return result

    # after checking `len(s)` because `s[indx]` could raise error
    # key_digit = s[indx]
    # key_chars = d[key_digit]
    # print(f"[DEBUG] {key_digit = }, {key_chars = }")

    if len(result) == 0:
        result.extend(d[s[indx]])  # without `result =`
        # result.extend(key_chars)  # without `result =`
    else:
        new_result = []  # create new list which will have more items

        for item in result:
            # for char in d[s[indx]]:
            #    new_result.append(item + char)
            new_result.extend([item + char for char in d[s[indx]]])
            # new_result.extend([item + char for char in key_chars])

        result = new_result  # replace old `result` with new list

    # print(f"[DEBUG] {result = }")
    # print("[DEBUG] -----")

    return keypad_combination(d, s, result, indx + 1)


# --- test ---

result = keypad_combination(d, "573", [], 0)
print(result)


# --- result ---

# ['mug', 'muh', 'mui', 'mvg', 'mvh', 'mvi', 'nug', 'nuh', 'nui', 'nvg', 'nvh', 'nvi', 'oug', 'ouh', 'oui', 'ovg', 'ovh', 'ovi', 'pug', 'puh', 'pui', 'pvg', 'pvh', 'pvi']