Recipe 2.23. Reading an Unbuffered Character in a Cross-Platform Way
Credit: Danny Yoo
Problem
Your application needs to read single
characters, unbuffered, from standard input, and it needs to work on
both Windows and Unix-like systems.
Solution
When we need a cross-platform solution, starting with
platform-dependent ones, we need to wrap the different solutions so
that they look the same:try:
from msvcrt import getch
except ImportError:
''' we're not on Windows, so we try the Unix-like approach '''
def getch( ):
import sys, tty, termios
fd = sys.stdin.fileno( )
old_settings = termios.tcgetattr(fd)
try:
tty.setraw(fd)
ch = sys.stdin.read(1)
finally:
termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
return ch
Discussion
On Windows,
the standard Python library module msvcrt offers
the handy getch function to read one character,
unbuffered, from the keyboard, without echoing it to the screen.
However, this module is not part of the standard Python library on
Unix and Unix-like platforms, such as Linux and Mac OS X. On such
platforms, we can get the same functionality with the
tty and termios modules of the
standard Python library (which, in turn, are not present on
Windows).
The key point is that in application-level code,
we should never have to worry about such issues; rather, we should
write our application code in platform-independent ways, counting on
library functions to paper over the differences between platforms.
The Python Standard Library fulfills that role admirably for most
tasks, but not all, and the problem posed by this recipe is an
example of one for which the Python Standard Library
doesn't directly supply a cross-platform solution.When we can't find a ready-packaged cross-platform
solution in the standard library, we should package it anyway as part
of our own additional custom library. This recipe's
Solution, besides solving the specific task of the recipe, also shows
one good general way to go about such packaging. (Alternatively, you
can test sys.platform, but I prefer the approach
shown in this recipe.)Your own library module should try to import the
standard library module it needs on a certain platform within a
TRy clause and include a corresponding
except ImportError clause that
is triggered when the module is running on a different platform. In
the body of that except clause, your own library
module can apply whatever alternate approach will work on the
different platform. In some rare cases, you may need more than two
platform-dependent approaches, but most often you'll
need one approach on Windows and only one other approach to cover all
other platforms. This is because most non-Windows platforms today are
generally Unix or Unix-like.
See Also
Library Reference and Python in a
Nutshell docs for msvcrt,
tty, and termios. |
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