A new to Python question

[David]

Hi I'm trying to teach myself python and so far to good, but I'm having
a bit of trouble getting a function to work the way I think it should
work. Right now I'm taking a simple program I wrote in Fortran and
trying to do it in Python. I got it to work, but now I'm trying to
modularize it. My fortran program uses a subroutine and I was trying
to do the same thing in Python. But I'm still new so I'm having
trouble understanding what I'm doing wrong. Here is my code:

#! /usr/bin/python
#This program takes two vectors and multiplies them
#against a 10X10 array. It also then gives the dot product,
#sum, and max value of the array.

import Numeric
def abc(array1,arra y2,dotprod,sum, maxvalue):
"""Takes two arrays and performs predetermined calculations,
Then returns the solutions back as the same array, along
with the dot product, sum, and max value of the array."""
#TODO: Get this damn thing working!!
print "Array 1 in:",array1 #Debug
data = Numeric.zeros(( 10,10))
for i in range(10):
for j in range(10):
data[i,j] = (i+1)+(j+1)

e = Numeric.matrixm ultiply(data, array1)
g = Numeric.matrixm ultiply(Numeric .transpose(data ),array2)
array1 = e
array2 = g
dotprod = Numeric.dot(arr ay1,array2)
sum = Numeric.sum(arr ay1)
maxvalue = array2[Numeric.argmax( array2)]
print "Array 1 out:",array1 #Debug

return array1,array2,d otprod,sum,maxv alue #<<-- Not working as I
thought it would.

x = Numeric.arange( 1,11)
y = Numeric.arange( 1,11)*2
dotp,sumx,maxv = 0,0,0 #Is this the only way to declare a variable?

print 'Array X:',x
print 'Array Y:',y
abc(x,y,dotp,su mx,maxv)
print 'Calling function abc'
print 'Array X:',x
print 'Array Y:',y
print 'Dot Product of X and Y:',dotp
print 'Sum of array X:',sumx
print 'Max value of array Y:',maxv

If you run it the data gets passed to the function just fine and it
finds the right numbers. Its just getting it to pass them back thats
not working. I put some print statements inside the function just to
see how the data gets passed. So any ideas that would help me? If you
want to see the fortran code just email me.

David

[Bernd Nawothnig]

On 2005-05-14, David wrote:

abc(x,y,dotp,su mx,maxv)

(x,y,dotp,sumx, maxv) = abc(x,y,dotp,su mx,maxv)


Bernd

--
Those who desire to give up freedom in order to gain security,
will not have, nor do they deserve, either one. [T. Jefferson]

[Philippe C. Martin]

Hi,

You're thinking you're passing the arguments as reference (look at mutable
vs non-mutable)

Your function returns the values in a tupple (x,y,...); you need to fetch
the values from that tupple

Regards,

Philippe

David wrote:

Hi I'm trying to teach myself python and so far to good, but I'm having
a bit of trouble getting a function to work the way I think it should
work. Right now I'm taking a simple program I wrote in Fortran and
trying to do it in Python. I got it to work, but now I'm trying to
modularize it. My fortran program uses a subroutine and I was trying
to do the same thing in Python. But I'm still new so I'm having
trouble understanding what I'm doing wrong. Here is my code:

#! /usr/bin/python
#This program takes two vectors and multiplies them
#against a 10X10 array. It also then gives the dot product,
#sum, and max value of the array.

import Numeric
def abc(array1,arra y2,dotprod,sum, maxvalue):
"""Takes two arrays and performs predetermined calculations,
Then returns the solutions back as the same array, along
with the dot product, sum, and max value of the array."""
#TODO: Get this damn thing working!!
print "Array 1 in:",array1 #Debug
data = Numeric.zeros(( 10,10))
for i in range(10):
for j in range(10):
data[i,j] = (i+1)+(j+1)

e = Numeric.matrixm ultiply(data, array1)
g = Numeric.matrixm ultiply(Numeric .transpose(data ),array2)
array1 = e
array2 = g
dotprod = Numeric.dot(arr ay1,array2)
sum = Numeric.sum(arr ay1)
maxvalue = array2[Numeric.argmax( array2)]
print "Array 1 out:",array1 #Debug

return array1,array2,d otprod,sum,maxv alue #<<-- Not working as I
thought it would.

x = Numeric.arange( 1,11)
y = Numeric.arange( 1,11)*2
dotp,sumx,maxv = 0,0,0 #Is this the only way to declare a variable?

print 'Array X:',x
print 'Array Y:',y
abc(x,y,dotp,su mx,maxv)
print 'Calling function abc'
print 'Array X:',x
print 'Array Y:',y
print 'Dot Product of X and Y:',dotp
print 'Sum of array X:',sumx
print 'Max value of array Y:',maxv

If you run it the data gets passed to the function just fine and it
finds the right numbers. Its just getting it to pass them back thats
not working. I put some print statements inside the function just to
see how the data gets passed. So any ideas that would help me? If you
want to see the fortran code just email me.

David

[Bernd Nawothnig]

On 2005-05-14, Philippe C. Martin wrote:

You're thinking you're passing the arguments as reference

That is the way Fortran handles them:

[...]

Right now I'm taking a simple program I wrote in Fortran

Bernd

--
Those who desire to give up freedom in order to gain security,
will not have, nor do they deserve, either one. [T. Jefferson]

[M.E.Farmer]

David wrote:

Hi I'm trying to teach myself python and so far to good, but I'm having a bit of trouble getting a function to work the way I think it should
work. Right now I'm taking a simple program I wrote in Fortran and
trying to do it in Python. I got it to work, but now I'm trying to
modularize it. My fortran program uses a subroutine and I was trying
to do the same thing in Python. But I'm still new so I'm having
trouble understanding what I'm doing wrong. Here is my code:

#! /usr/bin/python
#This program takes two vectors and multiplies them
#against a 10X10 array. It also then gives the dot product,
#sum, and max value of the array.

import Numeric
def abc(array1,arra y2,dotprod,sum, maxvalue):
"""Takes two arrays and performs predetermined calculations,
Then returns the solutions back as the same array, along
with the dot product, sum, and max value of the array."""
#TODO: Get this damn thing working!!
print "Array 1 in:",array1 #Debug
data = Numeric.zeros(( 10,10))
for i in range(10):
for j in range(10):
data[i,j] = (i+1)+(j+1)

e = Numeric.matrixm ultiply(data, array1)
g = Numeric.matrixm ultiply(Numeric .transpose(data ),array2)
array1 = e
array2 = g
dotprod = Numeric.dot(arr ay1,array2)
sum = Numeric.sum(arr ay1)
maxvalue = array2[Numeric.argmax( array2)]
print "Array 1 out:",array1 #Debug

return array1,array2,d otprod,sum,maxv alue #<<-- Not working as I
thought it would.

x = Numeric.arange( 1,11)
y = Numeric.arange( 1,11)*2
dotp,sumx,maxv = 0,0,0 #Is this the only way to declare a variable?

print 'Array X:',x
print 'Array Y:',y
abc(x,y,dotp,su mx,maxv)
print 'Calling function abc'
print 'Array X:',x
print 'Array Y:',y
print 'Dot Product of X and Y:',dotp
print 'Sum of array X:',sumx
print 'Max value of array Y:',maxv

If you run it the data gets passed to the function just fine and it
finds the right numbers. Its just getting it to pass them back thats
not working. I put some print statements inside the function just to
see how the data gets passed. So any ideas that would help me? If you want to see the fortran code just email me.

David
Hello David,
welcome to Python!
Python always returns 'something' from a function or method if nothing
is specified or there is no return you get an implicit None.
You have created a function that accepts a few arguments and processes
them then returns there value.
The problem is that you **have not** used the return values ;)
example:

def funk(first,seco nd,third):
return first,second,th ird

This can be like this:
print funk("theses three args can be anything",2,"th ree")

If you need to use the return values you need to assign them to a
"name" so you have a handle on them.
Variables are don't exist in Python there are only objects and names(
hence namespaces ), but not everyone is so strict and you still see
mention of 'variables' when they mean 'names'. ##dotp,sumx,max v = 0,0,0 # not needed here
print 'Array X:',x
print 'Array Y:',y
## Notice we assign the return values to names so we can access it later arr1,arr2,dotp, sumx,maxv = abc(x,y,0,0,0)
print 'Calling function abc'
print 'Array X:',arr1
print 'Array Y:',arr2
print 'Dot Product of X and Y:',dotp
print 'Sum of array X:',sumx
print 'Max value of array Y:',maxv
Or you could pack all return values into a tuple and access it thru
slices. ##dotp,sumx,max v = 0,0,0 # not needed here
print 'Array X:',x
print 'Array Y:',y
abcinfo = abc(x,y,0,0,0)
print 'Calling function abc'
print 'Array X:',abcinfo[0]
print 'Array Y:',abcinfo[1]
print 'Dot Product of X and Y:',abcinfo[2]
print 'Sum of array X:',abcinfo[3]
print 'Max value of array Y:',abcinfo[4]

Or you could use a dictionary, or etc...
The possibilities are endless.
Be sure to study up on namespaces, it will ease your Python woes.
Namespaces are the most fundamental part of Python that new users don't
understand. Namespace mastery will take you far.
Just remember there are only two scopes local and global ;)
http://docs.python.org
hth,
M.E.Farmer

[M.E.Farmer]

(x,y,dotp,sumx, maxv) = abc(x,y,dotp,su mx,maxv)
This will only create a tuple in memory that has no name to reference
it by!
How would you access the returned value?
If you want a tuple you need to assign all the return vales to a single
name.
mytup = abc(x,y,dotp,su mx,maxv)
M.E.Farmer

[Steven Bethard]

M.E.Farmer wrote:

(x,y,dotp,sumx, maxv) = abc(x,y,dotp,su mx,maxv)
This will only create a tuple in memory that has no name to reference
it by!

Huh? This binds the names "x", "y", "dotp", "sumx" and "maxv" to the
values returned by abc:

py> def abc(*args):
.... return args
....
py> (x,y,dotp,sumx, maxv) = abc(2,3,5,7,11)
py> x
2
py> y
3
py> dotp
5
py> sumx
7
py> maxv
11

Of course, the parentheses around x,y,dotp,sumx,m axv are unnecessary.

STeVe

[David]

Thank you very much. Tulpes are really neat now that I've looked at
them. So after just fixing it, I changed it up and I would like to
show it off now.

#! /usr/bin/python
#This program takes two vectors and multiplies them
#against a 10X10 array. It also then gives the dot product,
#sum, and max value of the array.

import Numeric
def abc(package):
"""Takes two arrays and performs predetermined calculations,
Then returns the solutions back as the same array, along
with the dot product, sum, and max value of the array.

Data slots:
0 - First Array
1 - Second Array
2 - Dot product
3 - Sum
4 - Max Value"""
f = Numeric.zeros(( 10,10))
for i in range(10):
for j in range(10):
f[i,j] = (i+1)+(j+1)

e = Numeric.matrixm ultiply(f, package[0])
g = Numeric.matrixm ultiply(Numeric .transpose(f),p ackage[1])
package[0] = e
package[1] = g
package[2] = Numeric.dot(pac kage[0],package[1])
package[3] = Numeric.sum(pac kage[0])
package[4] = package[1][Numeric.argmax( package[1])]
return package

data = [Numeric.arange( 1,11),Numeric.a range(1,11)*2,0 ,0,0]
#data = [Array X, Array Y, Dot product, Sum, Max Value]

print 'Array X:',data[0]
print 'Array Y:',data[1]

data = abc(data)

print 'Calling function abc'
print 'Array X:',data[0]
print 'Array Y:',data[1]
print 'Dot Product of X and Y:',data[2]
print 'Sum of array X:',data[3]
print 'Max value of array Y:',data[4]

I think its just wonderful now, but if you got any other suggestions,
Please do tell. Thanks everyone.

David

[David]

Hmm don't know what happened. I guess the formatting got all chewed up.

[Bernd Nawothnig]

On 2005-05-14, M.E.Farmer wrote: (x,y,dotp,sumx, maxv) = abc(x,y,dotp,su mx,maxv)
This will only create a tuple in memory that has no name to reference
it by!
Maybe. But it does not seem to hurt. And I am not sure the tupel _is_
really created in that situation.
How would you access the returned value?
If you want a tuple you need to assign all the return vales to a single
name.

We do not want the tuple.
Python 2.3.5 (#1, Apr 28 2005, 12:14:04)
[GCC 3.4.3-20050110 (Gentoo Linux 3.4.3.20050110-r2,
ssp-3.4.3.20050110-0, pie-
on linux2
Type "help", "copyright" , "credits" or "license" for more information.

def foo():
... return 1,2,3
...
(a,b,c)=foo()
print a,b,c 1 2 3
works.

Of course, you can omit the ():
a,b,c=foo()
print a,b,c

1 2 3

That makes no difference.


Bernd

--
Those who desire to give up freedom in order to gain security,
will not have, nor do they deserve, either one. [T. Jefferson]