[Tutor] Re: Shadow error

[Christopher Smith]

Kalle Svensson <kalle@gnupung.net> wrote:
| 
<cut>
| 
| I'd like to ask a question, anyway.  Why is Cristopher's code working?
|  When I try it with Python 2.1 I get
| 
| [ kalle aragorn ~ 00:59:52 ]$ python2.1 scopetest.py 
| scopetest.py:5: SyntaxWarning: local name 'n' in 'dig' shadows use of
| 'n' as global in nested scope 'lambda'
<cut>
| 
| without from __future__ import nested_scopes, and with it I get
| 
| [ kalle aragorn ~ 01:00:00 ]$ python2.1 scopetest.py 
| [0.14999999999999999, 0.56000000000000005, 0.17999999999999999]
| 
| no warning.  I have no idea how I'm supposed to get both warning and
| result, except perhaps by using 2.2?
| Please enlighten me.

When I retried it (after having ended my session for the day) I, too, got 
a traceback error and it wouldn't run at all.  And I thought that I 
noticed during my experimenting that sometimes I would get this error.  I
suspect it has something to do with the environment becoming corrupted
after
making modifications.  This behavior hasn't been consistent enough for
me to get a handle on.  Maybe, too, I did a run where I didn't call the 
function with problems but got the error.  Like happens with the following:

Here's one of the other scripts that invokes the error.  I just tried it
and 
did not get a traceback but did get the warning:

<Untitled Script 5>:13: SyntaxWarning: local name 'm' in 'mtrx' 
shadows use of 'm' as global in nested scope 'a'

def mtrx(m):
	def a(i,j):
		return m[i][j]
	return a
l=[[1,2],[3,4]]
a=mtrx(l)
# no traceback unless I uncomment the next line:  
# print a(1,2)


Here is a version that works without warnings.

def mtrx(l):
	'''Returns a function which will accessess l[i][j] as l(i,j).
	'''
	def a(i,j,m=l):
		return m[i][j]
	return a

l=[[1,2],[3,4]]
a=mtrx(l)
print a(1,1)

# results in
# 4

/c