Python readline, tab completion cycling with the Cmd interface
I am using the cmd.Cmd class in Python to offer a simple readline interface to my program.
Self contained example:
from cmd import Cmd
class CommandParser(Cmd):
def do_x(self, line):
pass
def do_xy(self, line):
pass
def do_xyz(self, line):
pass
if __name__ == "__main__":
parser = CommandParser()
parser.cmdloop()
Pressing tab twice will show possibilities. Pressing tab again does the same.
My question is, how do I get the options to cycle on the third tab press? In readline terms I think this is called Tab: menu-complete , but I can't see how to apply this to a Cmd instance.
I already tried:
readline.parse_and_bind('Tab: menu-complete')
Both before and after instantiating the parser instance. No luck.
I also tried passing "Tab: menu-complete" to the Cmd constructor. No Luck here either.
Anyone know how it's done?
Cheers!
The easiest trick would be to add a space after menu-complete :
parser = CommandParser(completekey="tab: menu-complete ")
The bind expression that is executed
readline.parse_and_bind(self.completekey+": complete")
will then become
readline.parse_and_bind("tab: menu-complete : complete")
Everything after the second space is acutally ignored, so it's the same as tab: menu-complete .
If you don't want to rely on that behaviour of readline parsing (I haven't seen it documented) you could use a subclass of str that refuses to be extended as completekey:
class stubborn_str(str):
def __add__(self, other):
return self
parser = CommandParser(completekey=stubborn_str("tab: menu-complete"))
self.completekey+": complete" is now the same as self.completekey .
Unfortunately, it seems as though the only way around it is to monkey-patch the method cmdloop from the cmd.Cmd class, or roll your own.
The right approach is to use "Tab: menu-complete" , but that's overriden by the class as shown in line 115: readline.parse_and_bind(self.completekey+": complete") , it is never activated. (For line 115, and the entire cmd package, see this: https://hg.python.org/cpython/file/2.7/Lib/cmd.py). I've shown an edited version of that function below, and how to use it:
import cmd
# note: taken from Python's library: https://hg.python.org/cpython/file/2.7/Lib/cmd.py
def cmdloop(self, intro=None):
"""Repeatedly issue a prompt, accept input, parse an initial prefix
off the received input, and dispatch to action methods, passing them
the remainder of the line as argument.
"""
self.preloop()
if self.use_rawinput and self.completekey:
try:
import readline
self.old_completer = readline.get_completer()
readline.set_completer(self.complete)
readline.parse_and_bind(self.completekey+": menu-complete") # <---
except ImportError:
pass
try:
if intro is not None:
self.intro = intro
if self.intro:
self.stdout.write(str(self.intro)+"n")
stop = None
while not stop:
if self.cmdqueue:
line = self.cmdqueue.pop(0)
else:
if self.use_rawinput:
try:
line = raw_input(self.prompt)
except EOFError:
line = 'EOF'
else:
self.stdout.write(self.prompt)
self.stdout.flush()
line = self.stdin.readline()
if not len(line):
line = 'EOF'
else:
line = line.rstrip('rn')
line = self.precmd(line)
stop = self.onecmd(line)
stop = self.postcmd(stop, line)
self.postloop()
finally:
if self.use_rawinput and self.completekey:
try:
import readline
readline.set_completer(self.old_completer)
except ImportError:
pass
# monkey-patch - make sure this is done before any sort of inheritance is used!
cmd.Cmd.cmdloop = cmdloop
# inheritance of the class with the active monkey-patched `cmdloop`
class MyCmd(cmd.Cmd):
pass
Once you've monkey-patched the class method, (or implemented your own class), it provides the correct behavior (albeit without highlighting and reverse-tabbing, but these can be implemented with other keys as necessary).
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