Importing an output from another function

[Byte]

Probably a stupid question, but I'm a newbie and this really pisses me
off. Run this script:

import random

def Func1():
choice = ('A', 'B', 'C')
output = random.choice(c hoice)

def Func2():
print output

Func1()
Func2()

And: an error message...... It says:

Traceback (most recent call last):
File "ptls-demo.py", line 11, in ?
Func2()
File "how -the-hell-do-i-fix-this.py", line 8, in Func2
print output
NameError: global name 'output' is not defined

Obviosly, I need to import the variable 'output' from Func1() into
Func2(), but how?

Thanks in advance,
-- /usr/bin/byte

[bearophileHUGS@lycos.com]

Re: Importing an output from another function

Generally, a name defined into a function can't be read outside of it,
so you have to return the function result explicitely:

import random

def Func1():
choice = ('A', 'B', 'C')
output = random.choice(c hoice)
return output

def Func2(item):
print item

output1 = Func1()
Func2(output1)


Bye,
bearophile

[Byte]

Re: Importing an output from another function

Great, thanks

-- /usr/bin/byte

[Byte]

Re: Importing an output from another function

Now what do I do if Func1() has multiple outputs and Func2() requires
them all to give its own output, as follows:

import random

def Func1():
choice = ('A', 'B', 'C')
output = random.choice(c hoice)
output2 = random.choice(c hoice)
return output
return output2

def Func2(item1, item2):
print item1, item2

output1 = Func1()
Func2(output1)

Thanks in advance,
-- /usr/bin/byte

[John Salerno]

Re: Importing an output from another function

Byte wrote:[color=blue]
> Now what do I do if Func1() has multiple outputs and Func2() requires
> them all to give its own output, as follows:[/color]

You can return them as a tuple:
[color=blue][color=green][color=darkred]
>>> def func1():[/color][/color][/color]
output1 = 'hi'
output2 = 'bye'
return (output1, output2)
[color=blue][color=green][color=darkred]
>>> def func2(data):[/color][/color][/color]
print data
[color=blue][color=green][color=darkred]
>>> func2(func1())[/color][/color][/color]
('hi', 'bye')

[color=blue]
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
> output2 = random.choice(c hoice)
> return output
> return output2[/color]

Only the first return statement would run in that code.

[James Stroud]

Re: Importing an output from another function

Byte wrote:[color=blue]
> Now what do I do if Func1() has multiple outputs and Func2() requires
> them all to give its own output, as follows:
>
> import random
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
> output2 = random.choice(c hoice)
> return output
> return output2[/color]

The function will return at "return output", so "return output2" will
never be reached.

[color=blue]
> def Func2(item1, item2):
> print item1, item2
>
> output1 = Func1()
> Func2(output1)
>
> Thanks in advance,
> -- /usr/bin/byte
>[/color]

Try this (I think its called "argument expansion", but I really don't
know what its called, so I can't point you to docs):

def Func1():
choice = ('A', 'B', 'C')
output = random.choice(c hoice)
output2 = random.choice(c hoice)
return output, output2

def Func2(*items):
print items

output = Func1()
Func2(output1)


BETTER:
=======

You can also make a "generator" (which I have made generalized, which
seems to be what you are striving for):


def Gener1(num):
choice = ('A', 'B', 'C')
for i in xrange(num):
yield random.choice(c hoice)

def Func2(item):
print item

for item in Gener1(2):
Func2(item)


James

--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/

[James Stroud]

Re: Importing an output from another function



Byte wrote:[color=blue]
> Now what do I do if Func1() has multiple outputs and Func2() requires
> them all to give its own output, as follows:
>
> import random
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
> output2 = random.choice(c hoice)
> return output
> return output2[/color]


The function will return at "return output", so "return output2" will
never be reached.
[color=blue]
> def Func2(item1, item2):
> print item1, item2
>
> output1 = Func1()
> Func2(output1)
>
> Thanks in advance,
> -- /usr/bin/byte
>[/color]


Try this (I think its called "argument expansion", but I really don't
know what its called, so I can't point you to docs):

def Func1():
choice = ('A', 'B', 'C')
output = random.choice(c hoice)
output2 = random.choice(c hoice)
return output, output2

def Func2(*items):
print items

output = Func1()
Func2(*output1)


BETTER:
=======

You can also make a "generator" (which I have made generalized, which
seems to be what you are striving for):


def Gener1(num):
choice = ('A', 'B', 'C')
for i in xrange(num):
yield random.choice(c hoice)

def Func2(item):
print item

for item in Gener1(2):
Func2(item)


James

--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/

[John Salerno]

Re: Importing an output from another function

James Stroud wrote:
[color=blue]
> Try this (I think its called "argument expansion", but I really don't
> know what its called, so I can't point you to docs):
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
> output2 = random.choice(c hoice)
> return output, output2
>
> def Func2(*items):
> print items
>
> output = Func1()
> Func2(*output1)[/color]

I was wondering about '*items' when I wrote my response. I left out the
asterisk in my version and it still seems to work. Is it necessary?

[James Stroud]

Re: Importing an output from another function

John Salerno wrote:[color=blue]
> James Stroud wrote:
>[color=green]
>> Try this (I think its called "argument expansion", but I really don't
>> know what its called, so I can't point you to docs):
>>
>> def Func1():
>> choice = ('A', 'B', 'C')
>> output = random.choice(c hoice)
>> output2 = random.choice(c hoice)
>> return output, output2
>>
>> def Func2(*items):
>> print items
>>
>> output = Func1()
>> Func2(*output1)[/color]
>
>
> I was wondering about '*items' when I wrote my response. I left out the
> asterisk in my version and it still seems to work. Is it necessary?[/color]

Yours is better, after I wrote mine, I realized the asterisk was
unnecessary for this particular example, except that it makes Func2 more
general.

James

--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/

[John Salerno]

Re: Importing an output from another function

James Stroud wrote:
[color=blue]
> Yours is better, after I wrote mine, I realized the asterisk was
> unnecessary for this particular example, except that it makes Func2 more
> general.[/color]

Yeah, I tested it. Func2 prints a tuple of a tuple when the asterisk is
used.

But your generator still wins. :)

[James Stroud]

Re: Importing an output from another function

John Salerno wrote:[color=blue]
> James Stroud wrote:
>
> Try this (I think its called "argument expansion", but I really[/color]
don't[color=blue]
> know what its called, so I can't point you to docs):
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
> output2 = random.choice(c hoice)
> return output, output2
>
> def Func2(*items):
> print items
>
> output = Func1()
> Func2(*output1)
>
>
> I was wondering about '*items' when I wrote my response. I left out[/color]
the[color=blue]
> asterisk in my version and it still seems to work. Is it necessary?
>[/color]
Yours is better, after I wrote mine, I realized the asterisk was
unnecessary for this particular example, except that it makes Func2
more
general.

James

--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/

[Terry Hancock]

Re: Importing an output from another function

On 17 Mar 2006 12:15:28 -0800
"Byte" <eoinrogers@gma il.com> wrote:[color=blue]
> Probably a stupid question, but I'm a newbie and this
> really pisses me off. Run this script:
>
> import random
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
>
> def Func2():
> print output
>
> Func1()
> Func2()[/color]

Several possible solutions. The simplest (but least
informative):

"""
import random

def Func1():
global output
choice = ('A', 'B', 'C')
output = random.choice(c hoice)

def Func2():
print output

Func1()
Func2()
"""

i.e. make output a global variable

But as has already been pointed out, you aren't really using
the nature of functions here. Better:

"""
import random

def Func1():
return random.choice(( 'A', 'B', 'C'))

def Func2(output):
print output

Func2(Func1())
"""

You later ask about returning multiple values. Python is
pretty cool in this respect -- you can return multiple
values in a tuple, which can then be "unpacked"
automatically. This gives you a nice many-to-many idiom for
function calls, e.g.:

x, y = random_point(x_ min, x_max, y_min, y_max)

And if you need to pass that to a function which takes two
arguments (x,y), you can:

set_point(*rand om_point(x_min, x_max, y_min, y_max))

Of course, some people would rather see that expanded out,
and indeed, too many nested function calls can be hard on
the eyes, so you might want to do this anyway:

x, y = random_point(x_ min, x_max, y_min, y_max)
set_point(x, y)

or

P = random_point(x_ min, x_max, y_min, y_max)
set_point(P)

and of course, it's possible that the function requires the
arguments in a different order, e.g.:

x, y = random_point(1, 80,1,25)
set_rowcol(y, x, 'A')

or some such thing.

By far the coolest thing about tuple-unpacking, though, is
that this works like you'd expect it to:

x, y = y, x

instead of being a dumb mistake like this is:

x = y
y = x

which of course should be

temp = y
x = y
y = temp

But ewww that's ugly.

Cheers,
Terry

--
Terry Hancock (hancock@Anansi Spaceworks.com)
Anansi Spaceworks http://www.AnansiSpaceworks.com

[Paul Rubin]

Re: Importing an output from another function

"Byte" <eoinrogers@gma il.com> writes:[color=blue]
> Probably a stupid question, but I'm a newbie and this really pisses me
> off. Run this script:
>
> import random
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
>
> def Func2():
> print output
>
> Func1()
> Func2()[/color]

You could declare output to be global, but it's kind of poor style.
Preferable is something like:

def Func1():
choice = ('A', 'B', 'C')
output = random.choice(c hoice)
return output

def Func2(x):
print x

output = Func1() # this "output" is not the same as the one in Func1
Func2(output)

[Ben Cartwright]

Re: Importing an output from another function

James Stroud wrote:[color=blue]
> Try this (I think its called "argument expansion", but I really don't
> know what its called, so I can't point you to docs):
>
> def Func1():
> choice = ('A', 'B', 'C')
> output = random.choice(c hoice)
> output2 = random.choice(c hoice)
> return output, output2
>
> def Func2(*items):
> print items
>
> output = Func1()
> Func2(*output1)[/color]


Single asterisk == "arbitrary argument list". Useful in certain
patterns, but not something you use every day.

Documentation is in the tutorial:

http://www.python.org/doc/current/tut/node6.html#SECTION006730000000000000000

PS: Like "self" for class instance methods, "*args" is the
conventional name of the arbitrary argument list.

--Ben

[Byte]

Re: Importing an output from another function

"Try this (I think its called "argument expansion", but I really don't
know what its called, so I can't point you to docs):"

This works, thanks. But how acn I get rid of the ugly surrounding
brackets and commas?

e.g. If the scripts overall output was (('B', 'C'),), how to change it
to just B C?