def source_token_lines(source: str) -> TSourceTokenLines:
    """Generate a series of lines, one for each line in `source`.

    Each line is a list of pairs, each pair is a token::

        [('key', 'def'), ('ws', ' '), ('nam', 'hello'), ('op', '('), ... ]

    Each pair has a token class, and the token text.

    If you concatenate all the token texts, and then join them with newlines,
    you should have your original `source` back, with two differences:
    trailing white space is not preserved, and a final line with no newline
    is indistinguishable from a final line with a newline.

    """

    ws_tokens = {token.INDENT, token.DEDENT, token.NEWLINE, tokenize.NL}
    line: list[tuple[str, str]] = []
    col = 0

    source = source.expandtabs(8).replace("\r\n", "\n")
    tokgen = generate_tokens(source)

    if env.PYBEHAVIOR.soft_keywords:
        soft_key_lines = find_soft_key_lines(source)
    else:
        soft_key_lines = set()

    for ttype, ttext, (sline, scol), (_, ecol), _ in _phys_tokens(tokgen):
        mark_start = True
        for part in re.split("(\n)", ttext):
            if part == "\n":
                yield line
                line = []
                col = 0
                mark_end = False
            elif part == "":
                mark_end = False
            elif ttype in ws_tokens:
                mark_end = False
            else:
                if env.PYBEHAVIOR.fstring_syntax and ttype == token.FSTRING_MIDDLE:
                    part = part.replace("{", "{{").replace("}", "}}")
                    ecol = scol + len(part)
                if mark_start and scol > col:
                    line.append(("ws", " " * (scol - col)))
                    mark_start = False
                tok_class = tokenize.tok_name.get(ttype, "xx").lower()[:3]
                if ttype == token.NAME:
                    if keyword.iskeyword(ttext):
                        # Hard keywords are always keywords.
                        tok_class = "key"
                    elif env.PYBEHAVIOR.soft_keywords and keyword.issoftkeyword(ttext):
                        # Soft keywords appear at the start of their line.
                        if len(line) == 0:
                            is_start_of_line = True
                        elif (len(line) == 1) and line[0][0] == "ws":
                            is_start_of_line = True
                        else:
                            is_start_of_line = False
                        if is_start_of_line and sline in soft_key_lines:
                            tok_class = "key"
                line.append((tok_class, part))
                mark_end = True
            scol = 0
        if mark_end:
            col = ecol

    if line:
        yield line
Generate a series of lines, one for each line in `source`.

    Each line is a list of pairs, each pair is a token::

        [('key', 'def'), ('ws', ' '), ('nam', 'hello'), ('op', '('), ... ]

    Each pair has a token class, and the token text.

    If you concatenate all the token texts, and then join them with newlines,
    you should have your original `source` back, with two differences:
    trailing white space is not preserved, and a final line with no newline
    is indistinguishable from a final line with a newline.

    
coverage/phystokens.py