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# terminalsize.py - find size of terminal
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# Copyright (C) 2008 Canonical, Ltd.
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, version 3 of the License.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# Inspired by code by Chuck Blake, at
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# http://pdos.csail.mit.edu/~cblake/cls/cls.py, but rewritten in an
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# attempt to clarify things. This code is slightly tricky, so I thought
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# the extra clarity would be worth it.
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def get_terminal_size(fd=1):
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"""Return size of terminal attached to the standard output.
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Use ioctl(2) to query a terminal for its size, given a file
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descriptor attached to the terminal. Return (None, None) if this
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fails, otherwise a tuple (columns, rows).
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(The optional 'fd' argument can be set to whatever file
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descriptor you want to use. This is useful for unit tests.)
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# Do the ioctl call. termios.TIOCGWINSZ is the code to query
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# terminal size (see tty_ioctl(4), at least on Linux). We need
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# to give it a string of suitable size to use as the input
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# buffer for ioctl. Ioctl modifies the buffer and returns the
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# modified buffer as its return value.
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# The manual page specifies a struct winsize to be used, which
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# consists of four unsigned shorts. We use struct.calcsize to
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# compute the size of that.
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# Note that Blake's original code assumes only the first two
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# shorts in the struct are used, and that two shorts fit into
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# four bytes, which is probably true for all the relevant
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# platforms, but is cramped enough that it makes me feel icky.
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# Thus, I assume less. This will still break if the contents
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# of the struct change, but since that would change the system
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# call API, that's unlikely.
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buflen = struct.calcsize('hhhh')
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buf = fcntl.ioctl(fd, termios.TIOCGWINSZ, '\0' * buflen)
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# ioctl returns a binary buffer that represents the struct
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# at the C level. We unpack it with struct.unpack.
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tuple = struct.unpack('hhhh', buf)
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# If anything went wrong, we give up and claim we don't know.
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return tuple[0], tuple[1]
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computerjanitorapp/terminalsize.py
