[Tutor] cannonical matrix representation?

[Mike Cheponis]

What's the best way to represent a matrix M with 4 dimensions, such as 
M[x][y][z][t] where each element in the sparse matrix could be a simple number, 
or could be an executable Python function snipped that returns a value when 
that cell is evaluated?

The user of the program will type in Python functions to be inserted into 
particular cells in the 4-D matrix.

I did't see any package that exactly does this; do I write my own Matrix class 
and base it on lists?

Thanks!  -Mike

p.s. This seems to me like it ought to be built into the base language - 
multidimensional object arrays. (Indeed, maybe it is, and I'm just too dense to 
notice!)

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[Tutor] Simple Tkinter question

[Mike Cheponis]

I'm trying to update an Entry's textvariable several times within my Button 
handler, like so:

from Tkinter import *
from time import *

def my_update():
   for i in range(3):
 tv.set("Now it's %d"%i)
 sleep(1)

root=Tk()
tv=StringVar()
Entry(textvariable=tv).pack()
tv.set("Initial Value of StringVar")
Button(text="Update", command=my_update).pack()
root.mainloop()


What happens when I hit the Update button is a 3-second pause, then "Now it's 
2" is displayed.

What I expected to see in the Entry was:

"Now it's 0"  (right away)
"Now it's 1"  (after 1 second pause)
"Now it's 2"  (after another 1 second pause)


Any idea what's going on here?  Why doesn't "tv.set("") happen 
immediately?

Thanks, -Mike

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Re: [Tutor] Combining dictionaries

[Mike Cheponis]

On Tue, 6 Sep 2005, Danny Yoo wrote:

>> No, that's not what he wants.
>>
>> He wants c = a + b to work when a and b are dictionaries.
>>
>> Why is Python broken in such an obvious way?


> It might not be obvious.  If a and b overlap so that they share keys, then
> we might have the following situation:

I did consider that, but of course, "update" has to deal with that issue 
already.



>c1 = a + b
>c2 = b + a
>
> Are c1 and c2 the same?

Answer: maybe


> One possible problem is that this kind of "merging" operation on
> dictionaries isn't "commutative".  And notationally, addition is supposed
> to be so.  Forcing the notation of arithmetic on dictionaries is
> seductive, but it can invite logical errors.

( See my note, below, on the "*" operator [1]. )


Then use an operator like "++" which would be non-commutative "addition".

>>> a={1:1,2:2}
>>> b={2:22,3:3}
>>> c=dict(a)
>>> c.update(b) # This would be c = a ++ b
>>> c
{1: 1, 2: 22, 3: 3}

>>> c=dict(b)
>>> c.update(a) # This would be c = b ++ a
>>> c
{1: 1, 2: 2, 3: 3}


Seems like a straightforward improvement.

--

[1] Speaking of things that are suprising:


>>> "foo"   "bar "*3
'foobar foobar foobar '

>>> "foo" + "bar "*3
'foobar bar bar '


This also seems like a nasty bug (to me, at least).  Because one would think 
that the "*"
operator would bind more closely than the '"' or implied concatenation would.

How can I actively help fix these Python bugs?




> Best of wishes to you!

Same to you!


Thanks!  -Mike
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[Tutor] Combining dictionaries

[Mike Cheponis]

>Is this what you want ?
>
>c = dict(a)
>c.update(b)
>
>Pierre


>> Is there an easy way to combine dictionaries?
>>
>> a = {}
>> b = {}
>> 
>> a = {'a':'a', 'b':'b', 'c':'c'}
>> b = {'1':1, '2':2, '3':3}
>> c = a + b # doesn't seem to work
>> 
>> desired:
>> c = {'a':'a', 'b':'b', 'c':'c', '1':1, '2':2, '3':3}
>> 
>> Frank


No, that's not what he wants.

He wants c = a + b to work when a and b are dictionaries.

Why is Python broken in such an obvious way?

Thanks -Mike
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[Tutor] Case ?

[Mike Cheponis]

Why does Python not have a "case" statement, like C?

Thanks!  -Mike
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