Python dictionary deepcopy

The documentation makes it pretty clear that you're getting new copies, not references. Deepcopy creates deep copies for built in types, with various exceptions and that you can add custom copy operations to your user-defined objects to get deep copy support for them as well. If you're not sure, well that's what unit testing is for.

I know it isn't answering your question but I think it's noteworthy for people looking at this question.

If the data you're copying is simple in nature deepcopy might be overkill. With simple in nature I mean if your data is representable as Json. Let me illustrate with code:

I've used http://www.json-generator.com/ to get some sample json data.

def deepCopyList(inp):    for vl in inp:        if isinstance(vl, list):            yield list(deepCopyList(vl))        elif isinstance(vl, dict):            yield deepCopyDict(vl)def deepCopyDict(inp):    outp = inp.copy()    for ky, vl in outp.iteritems():        if isinstance(vl, dict):            outp[ky] = deepCopyDict(vl)              elif isinstance(vl, list):            outp[ky] = list(deepCopyList(vl))      return outpdef simpleDeepCopy(inp):    if isinstance(inp, dict):        return deepCopyDict(inp)    elif isinstance(inp, list):        return deepCopyList(inp)    else:        return inpif __name__ == '__main__':    import simplejson as json    import time    from copy import deepcopy    fl = open('sample.json', 'r')    sample = json.load(fl)    start = time.time()    for _ in xrange(10000):        tmp = simpleDeepCopy(sample)    end = time.time()    print 'simpleDeepCopy: ' + str(end - start)    start = time.time()    for _ in xrange(10000):        tmp = deepcopy(sample)    end = time.time()    print 'copy.deepcopy: ' + str(end - start)

output:

simpleDeepCopy: 0.0132050514221copy.deepcopy: 2.66142916679simpleDeepCopy: 0.0128579139709copy.deepcopy: 2.60736298561