how to deepcopy a slice object?

[Alexandre Guimond]

Hi all,

i'm trying to deepcopy a slice object but i get the following error.
Does anyone know a workaround?

ActivePython 2.4.3 Build 12 (ActiveState Software Inc.) based on
Python 2.4.3 (#69, Apr 11 2006, 15:32:42) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.

>>import copy
copy.deepcopy( slice( 1, 10, 2 ) )

Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "C:\Program Files\Python\lib\copy.py", line 204, in deepcopy
y = _reconstruct(x, rv, 1, memo)
File "C:\Program Files\Python\lib\copy.py", line 336, in _reconstruct
y = callable(*args)
File "C:\Program Files\Python\lib\copy_reg.py", line 92, in
__newobj__
return cls.__new__(cls, *args)
TypeError: slice expected at least 1 arguments, got 0

thx for any help.

[Simon Forman]

Alexandre Guimond wrote:

Hi all,

i'm trying to deepcopy a slice object but i get the following error.
Does anyone know a workaround?

ActivePython 2.4.3 Build 12 (ActiveState Software Inc.) based on
Python 2.4.3 (#69, Apr 11 2006, 15:32:42) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.

>import copy
copy.deepcopy( slice( 1, 10, 2 ) )

Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "C:\Program Files\Python\lib\copy.py", line 204, in deepcopy
y = _reconstruct(x, rv, 1, memo)
File "C:\Program Files\Python\lib\copy.py", line 336, in _reconstruct
y = callable(*args)
File "C:\Program Files\Python\lib\copy_reg.py", line 92, in
__newobj__
return cls.__new__(cls, *args)
TypeError: slice expected at least 1 arguments, got 0

thx for any help.

Why would you want to [deep]copy a slice object?

Anyway, I don't know much about them, other than that they are
slightly unusual objects that play a very restricted role in python,
rather like the Ellipsis.

Workarounds are possible, I think, but really you almost certainly
don't need to do this.

Peace,
~Simon

[Alexandre Guimond]

Here is my reason:

I have an object that contrains a 2D regular grid (matrix). In this
regular grid, I place points at regular intervals. In essence, i have
something like (my code is obviously more complex, this is just to show
what I want to do)

obj.grid = numpy.zeros( ( 100, 100 ) )
obj.grid[ obj.y1: obj.y2 : obj.ys, obj.x1 : obj.x2 : obj.xs ] =
embedded_parameters
result = somefunc( obj.grid )

My goal was to reduce the number of elements in my obj object by
replacing y1, y2, ys, and x1, x2, xs by 2 slice objects, and then do:

obj.grid[ obj.slicey, obj.slicex ] = embedded_parameters

But when I do this and then try to deepcopy my object, it doesn't work,
as in the example below.

Its not a big thing. I just liked the idea of having less elements in
my obj class and actually modeling my slice concept by a slice object,
specially since i'm going to 3D and 4D grid, and its somewhat annoying
to carry so many indices in my class definition.

Simon Forman wrote:

Alexandre Guimond wrote:

Hi all,

i'm trying to deepcopy a slice object but i get the following error.
Does anyone know a workaround?

ActivePython 2.4.3 Build 12 (ActiveState Software Inc.) based on
Python 2.4.3 (#69, Apr 11 2006, 15:32:42) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.

>>import copy
>>copy.deepcopy( slice( 1, 10, 2 ) )

Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "C:\Program Files\Python\lib\copy.py", line 204, in deepcopy
y = _reconstruct(x, rv, 1, memo)
File "C:\Program Files\Python\lib\copy.py", line 336, in _reconstruct
y = callable(*args)
File "C:\Program Files\Python\lib\copy_reg.py", line 92, in
__newobj__
return cls.__new__(cls, *args)
TypeError: slice expected at least 1 arguments, got 0

thx for any help.

Why would you want to [deep]copy a slice object?

Anyway, I don't know much about them, other than that they are
slightly unusual objects that play a very restricted role in python,
rather like the Ellipsis.

Workarounds are possible, I think, but really you almost certainly
don't need to do this.

Peace,
~Simon

[Duncan Booth]

Simon Forman wrote:

Why would you want to [deep]copy a slice object?

I would guess the original poster actually wanted to copy a data structure
which includes a slice object somewhere within it. That is a perfectly
reasonable albeit somewhat unusual thing to want, however it doesn't work.

Similarly in Python 2.4 you cannot deepcopy functions. That has been fixed
in Python 2.5 but I guess nobody has tried deepcopying slices before so
they haven't been fixed.

[Simon Forman]

Alexandre Guimond wrote:

Here is my reason:

I have an object that contrains a 2D regular grid (matrix). In this
regular grid, I place points at regular intervals. In essence, i have
something like (my code is obviously more complex, this is just to show
what I want to do)

obj.grid = numpy.zeros( ( 100, 100 ) )
obj.grid[ obj.y1: obj.y2 : obj.ys, obj.x1 : obj.x2 : obj.xs ] =
embedded_parameters
result = somefunc( obj.grid )

My goal was to reduce the number of elements in my obj object by
replacing y1, y2, ys, and x1, x2, xs by 2 slice objects, and then do:

obj.grid[ obj.slicey, obj.slicex ] = embedded_parameters

But when I do this and then try to deepcopy my object, it doesn't work,
as in the example below.

Its not a big thing. I just liked the idea of having less elements in
my obj class and actually modeling my slice concept by a slice object,
specially since i'm going to 3D and 4D grid, and its somewhat annoying
to carry so many indices in my class definition.

Simon Forman wrote:

Alexandre Guimond wrote:

Hi all,
>
i'm trying to deepcopy a slice object but i get the following error.
Does anyone know a workaround?
>
ActivePython 2.4.3 Build 12 (ActiveState Software Inc.) based on
Python 2.4.3 (#69, Apr 11 2006, 15:32:42) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.
>import copy
>copy.deepcopy( slice( 1, 10, 2 ) )
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "C:\Program Files\Python\lib\copy.py", line 204, in deepcopy
y = _reconstruct(x, rv, 1, memo)
File "C:\Program Files\Python\lib\copy.py", line 336, in _reconstruct
y = callable(*args)
File "C:\Program Files\Python\lib\copy_reg.py", line 92, in
__newobj__
return cls.__new__(cls, *args)
TypeError: slice expected at least 1 arguments, got 0
>
thx for any help.

Why would you want to [deep]copy a slice object?

Anyway, I don't know much about them, other than that they are
slightly unusual objects that play a very restricted role in python,
rather like the Ellipsis.

Workarounds are possible, I think, but really you almost certainly
don't need to do this.

Peace,
~Simon

Ah, so you *do* want to deepcopy slice objects.. Neat. :-)

I can't do that, but I can show you a couple of ways to deepcopy
objects that have slices as attributes.

First, if the __init__() method and its args are sufficient to recreate
your objects then you could do something like this:

class DeepCopyable0:

def __init__(self, x, y, z, a, b, c):
self.slicex = slice(x, y, z)
self.slicey = slice(a, b, c)

def __deepcopy__(self, memo):

# Create local vars for brevity.
sx, sy = self.slicex, self.slicey

# Create a new DeepCopyable0 instance.
return DeepCopyable0(
sx.start, sx.stop, sx.step,
sy.start, sy.stop, sy.step
)

|>d0 = DeepCopyable0(1, 2, 3, 4, 5, 6)
|>d0.slicex, d0.slicey
(slice(1, 2, 3), slice(4, 5, 6))
|>d1 = deepcopy(d0)
|>d1.slicex, d1.slicey
(slice(1, 2, 3), slice(4, 5, 6))

Otherwise, another way to do it would be to provide the pickling
protocol:

class DeepCopyable1:

def __init__(self, x, y, z, a, b, c):
# Pretend this was something more complicated.
self.slicex = slice(x, y, z)
self.slicey = slice(a, b, c)

def __getstate__(self):

state = self.__dict__.copy()

# Create local vars for brevity.
sx, sy = self.slicex, self.slicey

# Save the indices rather than the slices.
state['slicex'] = sx.start, sx.stop, sx.step
state['slicey'] = sy.start, sy.stop, sy.step

return state

def __setstate__(self, state):

# Recreate the slice objects.
state['slicex'] = slice(*state['slicex'])
state['slicey'] = slice(*state['slicey'])

self.__dict__.update(state)
|>d0 = DeepCopyable1(1, 2, 3, 4, 5, 6)
|>d0.slicex, d0.slicey
(slice(1, 2, 3), slice(4, 5, 6))
|>d1 = deepcopy(d0)
|>d1.slicex, d1.slicey
(slice(1, 2, 3), slice(4, 5, 6))

Circular references seem work fine here too. Observe:

|>d0 = DeepCopyable1(1, 2, 3, 4, 5, 6)
|>d0.rec = d0
|>d0
<delme.DeepCopyable instance at 0xb7d5cb2c>
|>d0.rec.rec #etc...
<delme.DeepCopyable instance at 0xb7d5cb2c>
|>d1 = deepcopy(d0)
|>d1
<delme.DeepCopyable instance at 0xb7d7878c>
|>d1.rec
<delme.DeepCopyable instance at 0xb7d7878c>

Since you're going to be using more dimensions, you could make python
do the work for you rather than cutting and pasting:

class DeepCopyable2:

# __init__() omitted...

def __getstate__(self):
state = self.__dict__.copy()

# Keep track of the slice attributes
slices = state['slices'] = []

# Convert slices to indices.
for attr, s in state.items():
if isinstance(s, slice):
state[attr] = s.start, s.stop, s.step
slices.append(attr)

return state

def __setstate__(self, state):

slices = state.pop('slices')

# Recreate the slice objects.
for attr in slices:
state[attr] = slice(*state[attr])

self.__dict__.update(state)
(I copied over the __init__() method from DeepCopyable for this
example.)
|>from delme import *
|>d0 = DeepCopyable2(1, 2, 3, 4, 5, 6)
|>d1 = deepcopy(d0)
|>d1.slicex, d1.slicey
(slice(1, 2, 3), slice(4, 5, 6))

HTH. :)

I haven't used numpy (yet) and I've never explicitly used slice
objects, so the idea of storing and copying them struck me funny. I
find it very interesting and amusing that someone somewhere has a use
for them like this.

Peace,
~Simon

[Simon Forman]

Duncan Booth wrote:

Simon Forman wrote:

Why would you want to [deep]copy a slice object?

I would guess the original poster actually wanted to copy a data structure
which includes a slice object somewhere within it. That is a perfectly
reasonable albeit somewhat unusual thing to want, however it doesn't work.

I figured it was either something like that or something really wacky.
:-) Either way I was curious.

Similarly in Python 2.4 you cannot deepcopy functions. That has been fixed
in Python 2.5 but I guess nobody has tried deepcopying slices before so
they haven't been fixed.

Shows how unusual it is.
Since slice objects appear to be immutable:

|>s = slice(1)
|>s
slice(None, 1, None)
|>s.start = 1
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'slice' object has only read-only attributes (assign to
..start)

etc...

fixing copy and deepcopy for slices would involve adding slice to the
tuple in this for statement in copy.py (starts on line 115 in my
version Python 2.4.3):

for t in (types.NoneType, int, long, float, bool, str, tuple,
frozenset, type, xrange, types.ClassType,
types.BuiltinFunctionType):
d[t] = _copy_immutable
and, lower down, around line 214, adding a line like this:

d[types.SliceType] = _deepcopy_atomic
I think I'll send a patch in in awhile. ;-)

Peace,
~Simon

[Alexandre Guimond]

thx for all the help simon. good ideas i can work with.

thx again.

alex.

Simon Forman wrote:

Alexandre Guimond wrote:

Here is my reason:

I have an object that contrains a 2D regular grid (matrix). In this
regular grid, I place points at regular intervals. In essence, i have
something like (my code is obviously more complex, this is just to show
what I want to do)

obj.grid = numpy.zeros( ( 100, 100 ) )
obj.grid[ obj.y1: obj.y2 : obj.ys, obj.x1 : obj.x2 : obj.xs ] =
embedded_parameters
result = somefunc( obj.grid )

My goal was to reduce the number of elements in my obj object by
replacing y1, y2, ys, and x1, x2, xs by 2 slice objects, and then do:

obj.grid[ obj.slicey, obj.slicex ] = embedded_parameters

But when I do this and then try to deepcopy my object, it doesn't work,
as in the example below.

Its not a big thing. I just liked the idea of having less elements in
my obj class and actually modeling my slice concept by a slice object,
specially since i'm going to 3D and 4D grid, and its somewhat annoying
to carry so many indices in my class definition.

Simon Forman wrote:

Alexandre Guimond wrote:
Hi all,

i'm trying to deepcopy a slice object but i get the following error.
Does anyone know a workaround?

ActivePython 2.4.3 Build 12 (ActiveState Software Inc.) based on
Python 2.4.3 (#69, Apr 11 2006, 15:32:42) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.
>>import copy
>>copy.deepcopy( slice( 1, 10, 2 ) )
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "C:\Program Files\Python\lib\copy.py", line 204, in deepcopy
y = _reconstruct(x, rv, 1, memo)
File "C:\Program Files\Python\lib\copy.py", line 336, in _reconstruct
y = callable(*args)
File "C:\Program Files\Python\lib\copy_reg.py", line 92, in
__newobj__
return cls.__new__(cls, *args)
TypeError: slice expected at least 1 arguments, got 0

thx for any help.
>
Why would you want to [deep]copy a slice object?
>
Anyway, I don't know much about them, other than that they are
slightly unusual objects that play a very restricted role in python,
rather like the Ellipsis.
>
Workarounds are possible, I think, but really you almost certainly
don't need to do this.
>
Peace,
~Simon

Ah, so you *do* want to deepcopy slice objects.. Neat. :-)

I can't do that, but I can show you a couple of ways to deepcopy
objects that have slices as attributes.

First, if the __init__() method and its args are sufficient to recreate
your objects then you could do something like this:

class DeepCopyable0:

def __init__(self, x, y, z, a, b, c):
self.slicex = slice(x, y, z)
self.slicey = slice(a, b, c)

def __deepcopy__(self, memo):

# Create local vars for brevity.
sx, sy = self.slicex, self.slicey

# Create a new DeepCopyable0 instance.
return DeepCopyable0(
sx.start, sx.stop, sx.step,
sy.start, sy.stop, sy.step
)

|>d0 = DeepCopyable0(1, 2, 3, 4, 5, 6)
|>d0.slicex, d0.slicey
(slice(1, 2, 3), slice(4, 5, 6))
|>d1 = deepcopy(d0)
|>d1.slicex, d1.slicey
(slice(1, 2, 3), slice(4, 5, 6))

Otherwise, another way to do it would be to provide the pickling
protocol:

class DeepCopyable1:

def __init__(self, x, y, z, a, b, c):
# Pretend this was something more complicated.
self.slicex = slice(x, y, z)
self.slicey = slice(a, b, c)

def __getstate__(self):

state = self.__dict__.copy()

# Create local vars for brevity.
sx, sy = self.slicex, self.slicey

# Save the indices rather than the slices.
state['slicex'] = sx.start, sx.stop, sx.step
state['slicey'] = sy.start, sy.stop, sy.step

return state

def __setstate__(self, state):

# Recreate the slice objects.
state['slicex'] = slice(*state['slicex'])
state['slicey'] = slice(*state['slicey'])

self.__dict__.update(state)
|>d0 = DeepCopyable1(1, 2, 3, 4, 5, 6)
|>d0.slicex, d0.slicey
(slice(1, 2, 3), slice(4, 5, 6))
|>d1 = deepcopy(d0)
|>d1.slicex, d1.slicey
(slice(1, 2, 3), slice(4, 5, 6))

Circular references seem work fine here too. Observe:

|>d0 = DeepCopyable1(1, 2, 3, 4, 5, 6)
|>d0.rec = d0
|>d0
<delme.DeepCopyable instance at 0xb7d5cb2c>
|>d0.rec.rec #etc...
<delme.DeepCopyable instance at 0xb7d5cb2c>
|>d1 = deepcopy(d0)
|>d1
<delme.DeepCopyable instance at 0xb7d7878c>
|>d1.rec
<delme.DeepCopyable instance at 0xb7d7878c>

Since you're going to be using more dimensions, you could make python
do the work for you rather than cutting and pasting:

class DeepCopyable2:

# __init__() omitted...

def __getstate__(self):
state = self.__dict__.copy()

# Keep track of the slice attributes
slices = state['slices'] = []

# Convert slices to indices.
for attr, s in state.items():
if isinstance(s, slice):
state[attr] = s.start, s.stop, s.step
slices.append(attr)

return state

def __setstate__(self, state):

slices = state.pop('slices')

# Recreate the slice objects.
for attr in slices:
state[attr] = slice(*state[attr])

self.__dict__.update(state)
(I copied over the __init__() method from DeepCopyable for this
example.)
|>from delme import *
|>d0 = DeepCopyable2(1, 2, 3, 4, 5, 6)
|>d1 = deepcopy(d0)
|>d1.slicex, d1.slicey
(slice(1, 2, 3), slice(4, 5, 6))

HTH. :)

I haven't used numpy (yet) and I've never explicitly used slice
objects, so the idea of storing and copying them struck me funny. I
find it very interesting and amusing that someone somewhere has a use
for them like this.

Peace,
~Simon

[Simon Forman]

Alexandre Guimond wrote:

thx for all the help simon. good ideas i can work with.

thx again.

alex.

You're very welcome, a pleasure. ;-)

~Simon