import itertools


def get_sheet_idx(book, name):
    """Get a sheet by name from xlwt.Workbook, a strangely missing method.
    Returns None if no sheet with the given name is present.
    """
    # Note, we have to use exceptions for flow control because the
    # xlwt API is broken and gives us no other choice.
    try:
        for idx in itertools.count():
            sheet = book.get_sheet(idx)
            if sheet.name == name:
                return idx
    except IndexError:
        return None