matplotlib-users Mailing List for matplotlib

>>>>> "Chris" == Chris Barker <Chr...@no...> writes:


    Chris> no, I was a bit wrong. Python functions always return one
    Chris> object, and when it appears that you are returning multiple
    Chris> objects, you are really returning a single tuple with
    Chris> multiple objects in it. Have I got it right this time?

Sounds right to me.  Your answer does point to the danger of using
nargout in python

  ret = somefunc()
  i,j = ret  

If somefunc is relying on nargout, it will botch it.

I think the only sane use for nargout in python is in auto-conversion
scripts, and then with appropriate warnings. 

Thanks said, I would still like to have it, for that reason.

JDH

John Hunter wrote:

> What do you mean that python functions always return a tuple?  How
> about functions that return an int, or a string, or whatever?  

> 
>>>>def func(): return 1
>>>>type(func())
> 
> <type 'int'>
> 
> Do you mean that python functions that return tuples always return
> tuples <wink> ?

no, I was a bit wrong. Python functions always return one object, and 
when it appears that you are returning multiple objects, you are really 
returning a single tuple with multiple objects in it. Have I got it 
right this time?

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer
                                     		
NOAA/OR&R/HAZMAT         (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chr...@no...

>>>>> "Chris" == Chris Barker <Chr...@no...> writes:

    Chris> Darren Dale wrote:
    >> >I guess there is no way in Python of emulating >Matlab"s
    >> detection of the number of output arguments.  I just got a
    >> response from c.l.p. Somebody remembered seeing this at ASPN:
    >> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742
    >> expecting() is the workhorse, equivalent to Matlab's nargout:

    Chris> Very cool. but I'd caution against using it. I'd much
    Chris> rather see matplotlib be pythonesque than an exact
    Chris> duplicate of MATLAB. This is NOT pythonesque!

I tend to agree with the caution against using it.  But it would be
useful in some contexts, like converting existing matlab m-files to
python/numeric/numarray, the desire for which has occurred in some
contexts.  Last time the discussion came up, the lack of nargout was
raised as a problem for any converter code.


    Chris> Precisely speaking, python functions ALWAYS return just one
    Chris> object: A tuple. That tuple can contain any number of other
    Chris> objects, and sequence unpacking means it can look like
    Chris> you're returning multiple values, but you're not
    Chris> really. i.e.

What do you mean that python functions always return a tuple?  How
about functions that return an int, or a string, or whatever?  

>>> def func(): return 1
>>> type(func())
<type 'int'>

Do you mean that python functions that return tuples always return
tuples <wink> ?

JDH

Darren Dale wrote:
>  >I guess there is no way in Python of emulating
>  >Matlab"s detection of the number of output arguments.
> 
> I just got a response from c.l.p. Somebody remembered seeing this at ASPN:
> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742
> 
> expecting() is the workhorse, equivalent to Matlab's nargout:

Very cool. but I'd caution against using it. I'd much rather see 
matplotlib be pythonesque than an exact duplicate of MATLAB. This is NOT 
pythonesque!

Precisely speaking, python functions ALWAYS return just one object: A 
tuple. That tuple can contain any number of other objects, and sequence 
unpacking means it can look like you're returning multiple values, but 
you're not really. i.e.

def test():
	return (1,2,3) # same as return 1,2,3

# now call it:

a,b,c = test()
(a,b,c) = test()
x = test(); a,b,c = x
x = test(); a = x[0]; b = x[1]; c = x[2]

# Are all equivalent

if one uses the last two forms, expecting() will break.

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer
                                     		
NOAA/OR&R/HAZMAT         (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chr...@no...

Hi John,

>     >> I guess there is no way in Python of emulating Matlab"s
>     >> detection of the number of output arguments.
>
>     Darren> I just got a response from c.l.p. Somebody remembered
>     Darren> seeing this at ASPN:
>     Darren> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742
>
>     Darren> expecting() is the workhorse, equivalent to Matlab's
>     Darren> nargout:
>
>     Darren> import inspect,dis
>
> Hi Darren,
>
> Wow, I didn't know this was possible in python.  Does it work under
> python2.2?

The ASPN page says it has been tested on 2.3.3. I dont have a 2.2 installation 
handy to check it.

>
> Perhaps you would like to write up nargin and nargout function with
> some doc strings and send them my way?  I could add them to the matlab
> interface.  But we need to make sure they are 2.2 compliant.

I will give it a shot in my free time, but without getting into it, my next 
month is pretty full.

>
> As an aside, do we need nargout to make "find" work like matlab's?
> Isn't it enough just to check the shape of the input array and
> processing it one way for 1D arrays and another way for 2D arrays?
>

The problem is that mlab.find() is currently a thin wrapper around a numeric 
or numarray method, which only works for 1D arrays. ravelling the arrays 
passed to find would make it easy to continue using the method called by 
find(), but I had trouble figuring out how to process the 1xM results of that 
method back into an NxM or MxN array that could be used to index an N-D 
array.  

It would be nice to be able to address Numeric and numarray with a single 
index. Matlab does this. For example, if a=array([[1,2],[3,4]]), a[0] would 
be 1, a[1] would be 3 (Matlab's convention, again if memory serves.) 

-- 

Darren

>>>>> "Darren" == Darren Dale <dd...@co...> writes:

    >> I guess there is no way in Python of emulating Matlab"s
    >> detection of the number of output arguments.

    Darren> I just got a response from c.l.p. Somebody remembered
    Darren> seeing this at ASPN:
    Darren> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742

    Darren> expecting() is the workhorse, equivalent to Matlab's
    Darren> nargout:

    Darren> import inspect,dis

Hi Darren,

Wow, I didn't know this was possible in python.  Does it work under
python2.2?

Perhaps you would like to write up nargin and nargout function with
some doc strings and send them my way?  I could add them to the matlab
interface.  But we need to make sure they are 2.2 compliant.

As an aside, do we need nargout to make "find" work like matlab's?
Isn't it enough just to check the shape of the input array and
processing it one way for 1D arrays and another way for 2D arrays?
 
Cheers,
JDH

>>>>> "Jos=E9" =3D=3D Jos=E9 Alexandre Nalon <na...@te...> writes:

    Jos=E9> Hello, I think I've found a bug in mathtext - sorry if this
    Jos=E9> appeared before, I couldn't find it in the list archives.

    Jos=E9> When I try:

    Jos=E9> xlabel(r"$-(\Omega_a^' + \Omega_a)$")

    Jos=E9> I don't get what I expected. The label shows -\Omega_a and
    Jos=E9> stops there. Further tests showed that, whenever I try a
    Jos=E9> single quote in a mathtext string, the text is not rendered
    Jos=E9> from the quote on.

    Jos=E9> This might not be a bug, I might be doing something
    Jos=E9> wrong. If this is the case, please tell me how to do it
    Jos=E9> right.

I don't believe your use of ' is valid TeX.  Try
Omega_a^\prime

    Jos=E9> Thanks in advance.

Sure thing,
JDH

> xlabel(r"$-(\Omega_a^' + \Omega_a)$")
>
> I don't get what I expected. The label shows -\Omega_a and stops
> there. Further tests showed that, whenever I try a single quote
> in a mathtext string, the text is not rendered from the quote on.
>
> This might not be a bug, I might be doing something wrong. If
> this is the case, please tell me how to do it right.
>

try replacing ^' with ^\prime

Darren

Hello,

I think I've found a bug in mathtext - sorry if this appeared
before, I couldn't find it in the list archives.

When I try:

xlabel(r"$-(\Omega_a^' + \Omega_a)$")

I don't get what I expected. The label shows -\Omega_a and stops
there. Further tests showed that, whenever I try a single quote
in a mathtext string, the text is not rendered from the quote on.

This might not be a bug, I might be doing something wrong. If
this is the case, please tell me how to do it right.

Thanks in advance.

---
José Alexandre Nalon
na...@te...

 >I guess there is no way in Python of emulating
 >Matlab"s detection of the number of output arguments.

I just got a response from c.l.p. Somebody remembered seeing this at ASPN:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742

expecting() is the workhorse, equivalent to Matlab's nargout:

import inspect,dis

def expecting():
    """Return how many values the caller is expecting"""
    f = inspect.currentframe()
    f = f.f_back.f_back
    c = f.f_code
    i = f.f_lasti
    bytecode = c.co_code
    instruction = ord(bytecode[i+3])
    if instruction == dis.opmap['UNPACK_SEQUENCE']:
        howmany = ord(bytecode[i+4])
        return howmany
    elif instruction == dis.opmap['POP_TOP']:
        return 0
    return 1

def cleverfunc():
    howmany = expecting()
    if howmany == 0:
        print "return value discarded"
    if howmany == 2:
        return 1,2
    elif howmany == 3:
        return 1,2,3
    return 1

def test():
    cleverfunc()
    x = cleverfunc()
    print x
    x,y = cleverfunc()
    print x,y
    x,y,z = cleverfunc()
    print x,y,z

test()