def format_cell(src: str, *, fast: bool, mode: Mode) -> str:
    """Format code in given cell of Jupyter notebook.

    General idea is:

      - if cell has trailing semicolon, remove it;
      - if cell has IPython magics, mask them;
      - format cell;
      - reinstate IPython magics;
      - reinstate trailing semicolon (if originally present);
      - strip trailing newlines.

    Cells with syntax errors will not be processed, as they
    could potentially be automagics or multi-line magics, which
    are currently not supported.
    """
    validate_cell(src, mode)
    src_without_trailing_semicolon, has_trailing_semicolon = remove_trailing_semicolon(
        src
    )
    try:
        masked_src, replacements = mask_cell(src_without_trailing_semicolon)
    except SyntaxError:
        raise NothingChanged from None
    masked_dst = format_str(masked_src, mode=mode)
    if not fast:
        check_stability_and_equivalence(masked_src, masked_dst, mode=mode)
    dst_without_trailing_semicolon = unmask_cell(masked_dst, replacements)
    dst = put_trailing_semicolon_back(
        dst_without_trailing_semicolon, has_trailing_semicolon
    )
    dst = dst.rstrip("\n")
    if dst == src:
        raise NothingChanged from None
    return dst
Format code in given cell of Jupyter notebook.

    General idea is:

      - if cell has trailing semicolon, remove it;
      - if cell has IPython magics, mask them;
      - format cell;
      - reinstate IPython magics;
      - reinstate trailing semicolon (if originally present);
      - strip trailing newlines.

    Cells with syntax errors will not be processed, as they
    could potentially be automagics or multi-line magics, which
    are currently not supported.
    
src/black/__init__.py