Function pager_page

IPython/core/page.py:128–239

Display a string, piping through a pager after a certain length. strng can be a mime-bundle dict, supplying multiple representations, keyed by mime-type. The screen_lines parameter specifies the number of *usable* lines of your terminal screen (total lines minus lines you need to r

(strng, start=0, screen_lines=0, pager_cmd=None)

    #       screen_cols,'columns.')  # dbg

def pager_page(strng, start=0, screen_lines=0, pager_cmd=None) -> None:
    """Display a string, piping through a pager after a certain length.

    strng can be a mime-bundle dict, supplying multiple representations,
    keyed by mime-type.

    The screen_lines parameter specifies the number of *usable* lines of your
    terminal screen (total lines minus lines you need to reserve to show other
    information).

    If you set screen_lines to a number <=0, page() will try to auto-determine
    your screen size and will only use up to (screen_size+screen_lines) for
    printing, paging after that. That is, if you want auto-detection but need
    to reserve the bottom 3 lines of the screen, use screen_lines = -3, and for
    auto-detection without any lines reserved simply use screen_lines = 0.

    If a string won&#x27;t fit in the allowed lines, it is sent through the
    specified pager command. If none given, look for PAGER in the environment,
    and ultimately default to less.

    If no system pager works, the string is sent through a 'dumb pager'
    written in python, very simplistic.
    """
    
    # for compatibility with mime-bundle form:
    if isinstance(strng, dict):
        strng = strng['text/plain']

    # Ugly kludge, but calling curses.initscr() flat out crashes in emacs
    TERM = os.environ.get('TERM','dumb')
    if TERM in ['dumb','emacs'] and os.name != 'nt':
        print(strng)
        return
    # chop off the topmost part of the string we don't want to see
    str_lines = strng.splitlines()[start:]
    str_toprint = os.linesep.join(str_lines)
    num_newlines = len(str_lines)
    len_str = len(str_toprint)

    # Dumb heuristics to guesstimate number of on-screen lines the string
    # takes.  Very basic, but good enough for docstrings in reasonable
    # terminals. If someone later feels like refining it, it's not hard.
    numlines = max(num_newlines,int(len_str/80)+1)

    screen_lines_def = get_terminal_size()[1]

    # auto-determine screen size
    if screen_lines <= 0:
        try:
            screen_lines += _detect_screen_size(screen_lines_def)
        except (TypeError, UnsupportedOperation):
            print(str_toprint)
            return

    # print('numlines',numlines,'screenlines',screen_lines)  # dbg
    if numlines <= screen_lines :
        # print('*** normal print')  # dbg
        print(str_toprint)