Re: scared about refrences...


J. Clifford Dyer wrote:
SpreadTooThin wrote:
Steven D'Aprano wrote:
On Mon, 30 Oct 2006 13:10:47 -0800, SpreadTooThin wrote:

How do I specify or create deep copies of objects that may contain
other objects that may contain other object that may contain other
objects....
See the `copy` module especially `copy.deepcopy()`.

This appears to be the right thing to do to me.. (but what do I know?)
Yes, copy.deepcopy() is the thing you want.

But remember Fredrik's advice that well-designed Python code should not
need to copy data structures often. I don't think I've ever needed to use
deepcopy, and rarely copy.copy().

In general, functions should not modify their caller's data. So this is
bad practice:

def print_list(alist):
"""Print a sorted list"""
alist.sort() # modifies the caller's data -- bad!
for index, value in enumerate:
print "Value %s at index %d" % (index, value)

This is better:

def print_list(alist):
"""Print a sorted list"""
alist = alist[:] # makes a local shallow copy of the list
alist.sort() # safe to modify now
for index, value in enumerate:
print "Value %s at index %d" % (index, value)

But notice that you only need a shallow copy, not a deep copy, because you
aren't modifying the objects within the list, only the list itself.



I tried this which more closely resembles my project but this doesn't
work:
Unfortunately my crystal ball is back at the shop being repaired, so
you'll have to explain what "doesn't work" means in this case. Does it
raise an exception? If so, please post the exception. Does it do something
different from what you expected? Then what did you expect, and what did
it do?

I seems that some of the objects in the list don't get along well with
deep copy..
See my second example post that used deepcopy... When run blows up...

When it blows up, is there a lot of shrapnel, or just smoke and fire?
Is the shrapnel mostly metal, or is it plastic and glass?

In short, if we don't know what's happening, we can't help.
* Did the program spit out a bunch of text you didn't understand?
If so, show us the text. That text may be incomprehensible at first,
but it contains crucial clues.

* Did it close your python window without a word?
Tell us.

* Did your computer freeze up?
Tell us.

If you don't tell us what went wrong *exactly*, you won't get a
satisfactory answer.


I would assume that looking at the code you should be able to tell..
Silly me.. Here.. is the log.. If I were helping.. I would have cut
and pasted the code myself and ran it.. instead of trying to interpret
this...

array('H', [1, 2, 3]) ['a', 'b', 'c']
Traceback (most recent call last):
File
"/Volumes/Data/Users/bjobrien/Applications/Komodo.app/Contents/SharedSupport/dbgp/pythonlib/dbgp/client.py",
line 1806, in runMain
self.dbg.runfile(debug_args[0], debug_args)
File
"/Volumes/Data/Users/bjobrien/Applications/Komodo.app/Contents/SharedSupport/dbgp/pythonlib/dbgp/client.py",
line 1529, in runfile
h_execfile(file, args, module=main, tracer=self)
File
"/Volumes/Data/Users/bjobrien/Applications/Komodo.app/Contents/SharedSupport/dbgp/pythonlib/dbgp/client.py",
line 590, in __init__
execfile(file, globals, locals)
File "/Volumes/Data/Users/bjobrien/Desktop/pythonDICOM/Text-1.py",
line 20, in __main__
test(t)
File "/Volumes/Data/Users/bjobrien/Desktop/pythonDICOM/Text-1.py",
line 16, in test
t = copy.deepcopy(x)
File
"/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/copy.py",
line 174, in deepcopy
y = copier(x, memo)
File
"/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/copy.py",
line 305, in _deepcopy_inst
state = deepcopy(state, memo)
File
"/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/copy.py",
line 174, in deepcopy
y = copier(x, memo)
File
"/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/copy.py",
line 268, in _deepcopy_dict
y[deepcopy(key, memo)] = deepcopy(value, memo)
File
"/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/copy.py",
line 185, in deepcopy
y = copier(x, memo)
TypeError: __deepcopy__() takes no arguments (1 given)



Cheers,
Cliff

.

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