Function str_extractall

pandas/core/strings/accessor.py:4847–4882

(arr, pat, flags: int = 0)

def str_extractall(arr, pat, flags: int = 0) -> DataFrame:
    regex = re.compile(pat, flags=flags)
    # the regex must contain capture groups.
    if regex.groups == 0:
        raise ValueError("pattern contains no capture groups")

    if isinstance(arr, ABCIndex):
        arr = arr.to_series().reset_index(drop=True).astype(arr.dtype)

    columns = _get_group_names(regex)
    match_list = []
    index_list = []
    is_mi = arr.index.nlevels > 1

    for subject_key, subject in arr.items():
        if isinstance(subject, str):
            if not is_mi:
                subject_key = (subject_key,)

            for match_i, match_tuple in enumerate(regex.findall(subject)):
                if isinstance(match_tuple, str):
                    match_tuple = (match_tuple,)
                na_tuple = [np.nan if group == "" else group for group in match_tuple]
                match_list.append(na_tuple)
                result_key = (*subject_key, match_i)
                index_list.append(result_key)

    from pandas import MultiIndex

    index = MultiIndex.from_tuples(index_list, names=[*arr.index.names, "match"])
    dtype = _result_dtype(arr)

    result = arr._constructor_expanddim(
        match_list, index=index, columns=columns, dtype=dtype
    )
    return result