On Thu, Oct 5, 2017 at 12:24 PM, Stefan Ram <[email protected]> wrote:
> One might wish to implement a small language with these commands:
>
> F - move forward
> B - move backward
> L - larger stepsize
> S - smaller stepsize
>
> . One could start with the following pseudocode for a dictionary:
>
> { 'F': lambda: myturtle.forward( s ),
> 'B': lambda: myturtle.backward( s ),
> 'L': lambda: global s; s *= 2,
> 'S': lambda: global s; s /= 2 }
>
> . But lambda-expressions cannot contain statements.
>
> Any other suggestions?
There are a few options here. One is to make use of a simple
"collector decorator":
commands = {}
def cmd(f):
commands[f.__name__.upper()] = f
return f
@cmd
def f():
myturtle.forward( s )
@cmd
def b():
myturtle.backward( s )
@cmd
def l():
global siz
size *= 2
@cmd
def s():
global siz
size //= 2
(Also untested, but the pattern is one I've used many times.)
Another is to deploy the whole thing as a class, with no globals:
class Turtle:
def __init__(self):
self.size = ...
self.turtle = ...
def cmd_F(self):
self.turtle.forward(self.size)
def cmd_B(self):
self.turtle.backward(self.size)
def cmd_L(self):
self.size *= 2
def cmd_S(self):
self.size //= 2
Note that I've added "cmd_" in front of the names, which means you can
safely getattr(turtle, "cmd_" + letter) and be confident you won't
accidentally grab something that isn't a command.
(Note also that I used // for division. If your size is actually a
float, then change those back to single slashes.)
Either of these patterns would work fairly well. There are others,
too, but I'd be inclined to use one of these.
ChrisA
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