pylint/checkers/refactoring.py
def _is_trailing_comma(tokens, index):
    """Check if the given token is a trailing comma

    :param tokens: Sequence of modules tokens
    :type tokens: list[tokenize.TokenInfo]
    :param int index: Index of token under check in tokens
    :returns: True if the token is a comma which trails an expression
    :rtype: bool
    """
    token = tokens[index]
    if token.exact_type != tokenize.COMMA:
        return False
    # Must have remaining tokens on the same line such as NEWLINE
    left_tokens = itertools.islice(tokens, index + 1, None)
    same_line_remaining_tokens = list(
        itertools.takewhile(
            lambda other_token, _token=token: other_token.start[0] == _token.start[0],
            left_tokens,
        )
    )
    # Note: If the newline is tokenize.NEWLINE and not tokenize.NL
    # then the newline denotes the end of expression
    is_last_element = all(
        other_token.type in (tokenize.NEWLINE, tokenize.COMMENT)
        for other_token in same_line_remaining_tokens
    )
    if not same_line_remaining_tokens or not is_last_element:
        return False

    def get_curline_index_start():
        """Get the index denoting the start of the current line"""
        for subindex, token in enumerate(reversed(tokens[:index])):
            # See Lib/tokenize.py and Lib/token.py in cpython for more info
            if token.type in (tokenize.NEWLINE, tokenize.NL):
                return index - subindex
        return 0

    curline_start = get_curline_index_start()
    expected_tokens = {"return", "yield"}
    for prevtoken in tokens[curline_start:index]:
        if "=" in prevtoken.string or prevtoken.string in expected_tokens:
            return True
    return False
def _is_trailing_comma(tokens, index):
    """Check if the given token is a trailing comma

    :param tokens: Sequence of modules tokens
    :type tokens: list[tokenize.TokenInfo]
    :param int index: Index of token under check in tokens
    :returns: True if the token is a comma which trails an expression
    :rtype: bool
    """
    token = tokens[index]
    if token.exact_type != tokenize.COMMA:
        return False
    # Must have remaining tokens on the same line such as NEWLINE
    left_tokens = itertools.islice(tokens, index + 1, None)
    same_line_remaining_tokens = list(
        itertools.takewhile(
            lambda other_token, _token=token: other_token.start[0] == _token.start[0],
            left_tokens,
        )
    )
    # Note: If the newline is tokenize.NEWLINE and not tokenize.NL
    # then the newline denotes the end of expression
    is_last_element = all(
        other_token.type in (tokenize.NEWLINE, tokenize.COMMENT)
        for other_token in same_line_remaining_tokens
    )
    if not same_line_remaining_tokens or not is_last_element:
        return False

    def get_curline_index_start():
        """Get the index denoting the start of the current line"""
        for subindex, token in enumerate(reversed(tokens[:index])):
            # See Lib/tokenize.py and Lib/token.py in cpython for more info
            if token.type in (tokenize.NEWLINE, tokenize.NL):
                return index - subindex
        return 0

    curline_start = get_curline_index_start()
    expected_tokens = {"return", "yield"}
    for prevtoken in tokens[curline_start:index]:
        if "=" in prevtoken.string or prevtoken.string in expected_tokens:
            return True
    return False
Check if the given token is a trailing comma

    :param tokens: Sequence of modules tokens
    :type tokens: list[tokenize.TokenInfo]
    :param int index: Index of token under check in tokens
    :returns: True if the token is a comma which trails an expression
    :rtype: bool