On 10/5/17, Chris Angelico <ros...@gmail.com> wrote:
> On Thu, Oct 5, 2017 at 12:24 PM, Stefan Ram <r...@zedat.fu-berlin.de> 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
> --
> https://mail.python.org/mailman/listinfo/python-list
size = 2*size if size else 1
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