[Edu-sig] Python for Fun

[Kirby Urner]

>>Could also go:
>>
>>   self.connects.extend(inputs)  (is that 1.5 or later?)
>>
>Is this actually different from .append ?

It's different with later versions because in those append 
only accepts a single argument e.g.:

  >>> a = [1,2,3]
  >>> a.append([4,5,6])
  >>> a
  [1, 2, 3, [4, 5, 6]]
  >>> a = [1,2,3]
  >>> a.extend([4,5,6])
  >>> a
  [1, 2, 3, 4, 5, 6]

>I tried this and it seemed to work
>>>>
>>>> class con :
>...     def __init__ (self) :
>...             self.x = 5
>...     def prnt (selfi,c) :
>...             print self.x + c
>...
>>>> a = con()
>>>> b = [a,a,a]
>>>> map(lambda x: x.prnt(4), b)
>9
>9
>9
>[None, None, None]

If I use the following as my def of set in the Connector class:

    def set (self, value) :
        if self.value == value : return      # Ignore if no change
        self.value = value
        if self.activates : self.owner.evaluate()
        if self.monitor :
            print "Connector %s-%s set to %s" %
(self.owner.name,self.name,self.value)
        map(lambda con: con.set(value), self.connects)

Then upon import I get the warning:

d:\program files\python21\ocn\logic.py:25: SyntaxWarning: local name 
'value' in 'set' shadows use of 'value' as global in nested scope 'lambda'
  self.value = value

And the program crashes when using test4Bit:

 >>> test4Bit('1001','1110')
 Connector F0-Cin set to 0
 Traceback (most recent call last):
   File "<pyshell#40>", line 1, in ?
     test4Bit('1001','1110')
   File "d:\program files\python21\ocn\logic.py", line 124, in test4Bit
     F0.Cin.set(0)
   File "d:\program files\python21\ocn\logic.py", line 32, in set
     map(lambda con: con.set(value), self.connects)
   File "d:\program files\python21\ocn\logic.py", line 32, in <lambda>
     map(lambda con: con.set(value), self.connects)
 NameError: global name 'value' is not defined

However, if I insert:

from __future__ import nested_scopes

at the top of logic.py, then the code reloads w/o warnings and runs fine, 
because with nested scopes, lambda is perfectly able to see the value of 
'value' without needing to have that passed explicitly, as in:

    map(lambda con, value=value: con.set(value), self.connects)

...which works OK without the nested_scopes feature (probably in 
1.5.3 as well then).  It's this value=value stuff that the nested
scopes feature is designed to avoid/obviate.

Another experiment:  if I write a test module named test2.py with
the following function only:

 def test(x):
     y=5
     return map(lambda x: x+y, [x])

then on import I get the warning:

 >>> import test2
 d:\program files\python21\ocn\test2.py:1: SyntaxWarning: local name 
 'y' in 'test'  shadows use of 'y' as global in nested scope 'lambda'
   def test(x):

but if I add the line:

 from __future__ import nested_scopes 

to the top of the test2.py module and reload, then y is captured 
in the lambda.  No warnings, function works:

 >>> test2.test(10)
 [15]

What I find interesting is that I can't make the above function 
work in IDLE if I enter it at the command line, even if I enter
from __future__ import nested_scopes.  

In other words, whereas adding this 2.1-only import statement to 
the top of a module suppresses the warning and makes the code OK, 
entering this import statement at the command line doesn't salvage 
the code.

>>>>
>Speaking of scoping. If you get around to Lisp in Python, there's a 
>section on dynamic scoping with an example.
>
>Chris

I did study the Lisp example for awhile.  I'm always awed by LISP
and all that tail recursion.  Yet the LISP _does_ have looping 
syntax in the versions I've seen.  It's Scheme that stays purist
about using only recursion for looping, no?

>From what I understand of all this, Python isn't really tail 
recursive under the hood.  Am I right about that?

Building more complicated circuits with your logic gates would
be fun.  I've got this 'Beebop to the Boolean Boogie' book 
that'd make a good guide for testing out some other circuits.
Dunno when/if I'll get to do it.  

Kirby