> I noticed that bash uses $LINES, not $ROWS. I have renamed rows to lines everywhere, to follow existing convention.

The stty program has "rows" and "columns" commands to set the terminal
size. The tput programs has "cols" and "lines" commands to get the
terminal size. The curses library uses (y, x), e.g. it has a
getmaxyx() function. I don't know the most common term, lines or rows.

Extract of http://stackoverflow.com/questions/1780483/lines-and-columns-environmental-variables-lost-in-a-script
"The variables $LINES and $COLUMNS are shell variables, not
environmental variables, and thus are not exported to the child
process (...)"

If I understood correctly, LINES and COLUMNS environment variables are
only set by the user. In a bash script, these variables are wrapper to
ioctl().

The tput program reads TERM environment variable to decide if LINES
and COLUMNS are used or not:
"-Ttype indicates  the type of terminal.  Normally this option is
unnecessary, because the default is taken from the environment
variable TERM.  If -T is specified, then the shell variables LINES and
COLUMNS will be ignored,and the operating system will not be queried
for the actual screen size."

Extract of http://pubs.opengroup.org/onlinepubs/7908799/xbd/envvar.html :
------
COLUMNS
    A decimal integer > 0 used to indicate the user's preferred width
in column positions for the terminal screen or window. (See column
position .) If this variable is unset or null, the implementation
determines the number of columns, appropriate for the terminal or
window, in an unspecified manner. When COLUMNS is set, any
terminal-width information implied by TERM will be overridden. Users
and portable applications should not set COLUMNS unless they wish to
override the system selection and produce output unrelated to the
terminal characteristics. The default value for the number of column
positions is unspecified because historical implementations use
different methods to determine values corresponding to the size of the
screen in which the utility is run. This size is typically known to
the implementation through the value of TERM or by more elaborate
methods such as extensions to the stty utility, or knowledge of how
the user is dynamically resizing windows on a bit-mapped display
terminal. Users should not need to set this variable in the
environment unless there is a specific reason to override the
implementation's default behaviour, such as to display data in an area
arbitrarily smaller than the terminal or window.

LINES
    A decimal integer > 0 used to indicate the user's preferred number
of lines on a page or the vertical screen or window size in lines. A
line in this case is a vertical measure large enough to hold the
tallest character in the character set being displayed. If this
variable is unset or null, the implementation determines the number of
lines, appropriate for the terminal or window (size, terminal baud
rate, and so forth), in an unspecified manner. When LINES is set, any
terminal-height information implied by TERM will be overridden. Users
and portable applications should not set LINES unless they wish to
override the system selection and produce output unrelated to the
terminal characteristics. The default value for the number of lines is
unspecified because historical implementations use different methods
to determine values corresponding to the size of the screen in which
the utility is run. This size is typically known to the implementation
through the value of TERM or by more elaborate methods such as
extensions to the stty utility, or knowledge of how the user is
dynamically resizing windows on a bit-mapped display terminal. Users
should not need to set this variable in the environment unless there
is a specific reason to override the implementation's default
behaviour, such as to display data in an area arbitrarily smaller than
the terminal or window.
------

> The big remaining question seems to be one function vs. two functions.

Not exactly. I suggested to keep only the simple function in the os
module, and add maybe a function with a higher level API (using
environment variables) in another module (e.g. in shutil).