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ordered keywords?

P: n/a

Is there a way to preserve or capture the order which keywords are given?
def foo(**kwds): .... print kwds
.... foo(one=1, two=2, three=3)

{'three': 3, 'two': 2, 'one': 1}
I would love to reverse the *args, and **kwds as well so I can use kwds
to set defaults and initiate values and args to set the order of
expressions.
def foo(**__dict__, *args):
print args

print foo(x=10, y=20, x, y, x+y)
[10, 20, 30]
Ok, I know there is a lot of problems with that. The reason I would
like it is because I think there might be a use case for it where a
function iterates over *args in order, but uses kwds to set values.

def drawshapes(**inits, *args):
for obj in args:
obj.draw()

drawshapes( triangle=3, square=4, color=red,
polygon(triangle, color),
polygon(square, color) )

This comes close to the same pattern used in SVG and other formats where
you have definitions before expressions. If I use keywords only, It
won't keep the order, and if I use args before keywords, I have to
pre-assign temporary 'None' values to the arguments in the parent or
global scope.

Any ideas?

Cheers,
Ron







Oct 17 '05 #1
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5 Replies


P: n/a
Ron Adam wrote:

Is there a way to preserve or capture the order which keywords are given?
>>> def foo(**kwds): ... print kwds
... >>> foo(one=1, two=2, three=3)

{'three': 3, 'two': 2, 'one': 1}
I would love to reverse the *args, and **kwds as well so I can use kwds
to set defaults and initiate values and args to set the order of
expressions.
def foo(**__dict__, *args):
print args

print foo(x=10, y=20, x, y, x+y)
[10, 20, 30]


This is not simply about reversing the order of kwargs and args - this
would require that keyword args would create bindings to variable names
in the scope of the caller. Which is an enterily different beast. And a
major semantic change in python, so it's not possible or at least not
happening before Python 3K.

Regards,

Diez

Oct 17 '05 #2

P: n/a
Diez B. Roggisch wrote:
Ron Adam wrote:

Is there a way to preserve or capture the order which keywords are given?
>>> def foo(**kwds):

... print kwds
...
>>> foo(one=1, two=2, three=3)

{'three': 3, 'two': 2, 'one': 1}
I would love to reverse the *args, and **kwds as well so I can use
kwds to set defaults and initiate values and args to set the order of
expressions.
def foo(**__dict__, *args):
print args

print foo(x=10, y=20, x, y, x+y)
[10, 20, 30]

This is not simply about reversing the order of kwargs and args - this
would require that keyword args would create bindings to variable names
in the scope of the caller. Which is an enterily different beast. And a
major semantic change in python, so it's not possible or at least not
happening before Python 3K.

Regards,

Diez


Yes, I kind of thought it would be pretty major. What I'm asking is how
to get anything close to this behavior in the current Python 2.4 now
either with functions or with class's. Or a way to generalize it in a
nested data structure. But that runs into similar problems of self
reference.

I think the idea of putting the initialization first fits a lot of data
patterns. But I really don't know how the best way to implement that
would be.

I was hoping it just might be possible (for P3k?) to have an argument
list look to itself before looking to the caller, and then to globals
after that. And not create additional binding in the caller name space.
I think that would mean pre-creating the callee name space so it can
be accessed by later terms in the argument list before control and the
name space is handed over to the function. I think this would be
earlier evaluation instead of the late evaluation some want.
<clipped examples of possible stuff and jump to the interesting part>
def lamb(args):
for v in args: print v

def feedlamb():
print locals()
lamb( (lambda x=10, y=20: (x,y,x+y))() )
print locals()

feedlamb()

{}
10
20
30
{}
AND... (!?)
def lamb(args):
for v in args: print v

def feedlamb():
print locals()
y = 20
lamb( (lambda x=10: (x,y,x+y))() )
print locals()

feedlamb()

{}
10
20
30
{'y': 20}
Cool, this is the exact behavior I was thinking of, but without the
lambda if possible, and without all the extra parentheses. Anyway to
clean this up?

Maybe it wouldn't be as big a change as it seems? ;-)

Cheers,
Ron


Oct 17 '05 #3

P: n/a
Ron Adam wrote:

def lamb(args):
for v in args: print v

def feedlamb():
print locals()
y = 20
lamb( (lambda x=10: (x,y,x+y))() )
print locals()

feedlamb()

{}
10
20
30
{'y': 20}
Cool, this is the exact behavior I was thinking of, but without the
lambda if possible, and without all the extra parentheses. Anyway to
clean this up?

Maybe it wouldn't be as big a change as it seems? ;-)

Cheers,
Ron

Ok, this has a problem, there's no way to pass the values as keywords
also. The lambda's a bit too isolated. So the following doesn't work as
expected.

lamb( (lambda x=10: (x,y,x+y,{'x':x}))() )
Regards,
Ron
Oct 17 '05 #4

P: n/a
Ron Adam wrote:
drawshapes( triangle=3, square=4, color=red,
polygon(triangle, color),
polygon(square, color) )

This comes close to the same pattern used in SVG and other formats where
you have definitions before expressions.


Why is this better than the obvious
triangle=3
square=4
color=red
drawshapes(polygon(triangle, color),
polygon(square, color) )

or even
drawshapes(polygon(3, red),
polygon(4, red) )

which is concise and readable IMO...?

Kent
Oct 18 '05 #5

P: n/a
Kent Johnson wrote:
Ron Adam wrote:
drawshapes( triangle=3, square=4, color=red,
polygon(triangle, color),
polygon(square, color) )

This comes close to the same pattern used in SVG and other formats
where you have definitions before expressions.

Why is this better than the obvious
triangle=3
square=4
color=red
drawshapes(polygon(triangle, color),
polygon(square, color) )

or even
drawshapes(polygon(3, red),
polygon(4, red) )

which is concise and readable IMO...?

Kent


That example was over simplified quite a bit. :-)

The reason I'm trying to get named attributes is so I can change colors
or the text items later without having to recreate the object. The
objects I'm using are capable inheriting from other predefined objects
so you only have to add or modify it a tiny bit.

For example the following creates shapes that build on each other and
they all have a .draw() method to draw on a Tk canvas. In addition they
can be scaled, stretched and rotated. Well, the ones based on polygons
and lines can be rotated and stretched. I'm still working on how to do
that with arcs and text items.

## These are the most basic shape elements which use the
## Tkinter canvas items specified by the 'obj' attribute.

# base shapes.
text = Shape( obj='text', text='', fill='black', size=1,
font='', style='', pos=(0,0), points=(0,0) )

line = Shape( obj='line', arrow='none', fill='black', smooth='false',
pos=(0,0), width=.1, points=(-.5,0,.5,0), size=1,
rotate=0, center=(0,0) )

polygon = Shape( obj='polygon', fill='grey', outline='', size=1,
smooth='false', pos=(0,0), width=0, points=(0,0),
rotate=0, center=(0,0), ratio=(1,1) )

arc = Shape( obj='arc', fill='grey', outline='', pos=(0,0), width=0,
size=1, style='arc', start='0', extent='90',
points=(-.5,-.5,.5,.5) )

## This next group inherits from the shapes above and only
## needs to change what's different.

# shape variations
chord = arc(style='chord')
pie = arc(style='pieslice')
rectangle = polygon(points=[-.5,-.5,.5,-.5,.5,.5,-.5,.5])
triangle = polygon(points=getpolygon(3))
square = polygon(points=getpolygon(4))
octagon = polygon(points=getpolygon(8))
circle = polygon(smooth='true', points=getpolygon(16))

# The oval is stretched circle, which is a smoothed polygon.
# this can be rotated, the Tkinter oval can't.
oval = circle(ratio=(1,.7))
## Grouping combines the shapes together. Again only what is
## different needs to be changed, such as color or size and
## relative position. Any previously defined
## shapes can be combined to create complex new ones.

# CAUTION ICON
caution = Group(
triangle(pos=(6,5), size=75),
triangle(fill='yellow', size=75),
txt = text( text='!', font='times', style='bold',
pos=(0,-3), size=30,) )

# ERROR ICON
error = Group(
octagon(pos=(6,5), size=55),
octagon(fill='red', size=55),
circle(fill='white', size=37),
circle(fill='red', size=25),
line(fill='white', width=.2, rotate=45, size=28) )
## For this next group it would be nice if the bubbletip
## shape could be in the argument list, but it would need
## to be after the other refernces to it, and they
## would not find it. I did it this way to try out
## the idea of reusing objects, it would be no trouble
## just to duplicate the bubbletip in this case.

# QUESTION & INFO ICONS
bubbletip = polygon(points=[-5,10, 20,10, 30,30])
question = Group(
bubbletip(pos=(6,5)),
oval(pos=(6,5), size=60),
bubbletip(fill='lightblue'),
oval(fill='lightblue', size=60),
txt = text( text='?', font='times', style='bold',
size=25 ) )
## Here I just need to change the text element to 'i' to get
## the Info icon. Since it has a name we can do that.

info = question() # get a copy of question
info.txt.text = 'i' # change the '?' mark to 'i'
These can all be in a file ready to import and then you can use them
anywhere in Tkinter that accepts a normal canvas commands.

caution.draw(c, pos=(70,50), scale=.5) # small caution icon
error.draw(c, pos=(150,48), scale=3) # triple sized error icon
Now this all works wonderfully, but I can only have one named attribute
because I can't depend on the order a dictionary has. So I'm going to
probaby need to have a layer attribute. Thus the need for either
ordered keyword arguments, or a way to specify keywords as a variable
for the arguments list.

Eventually I will be able to mix groups and shapes together in other
groups by using them exactly like any other shape. So I can take a
image of a guy, add a hat, tilt the hat, and few other props, put some
text on it, and I have a nice illustration with very little effort.

There are still a lot of small details that still need to be worked out
before it's suitable for real use. It works now, but too much will
change as I add too it at this stage. ;-)

Cheers,
Ron








Oct 18 '05 #6

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