python list variable - copy.deepcopy vs pickle

2 Answers

You should be using deepcopy because it makes your code more readable. Using a serialization mechanism to copy objects in memory is at the very least confusing to another developer reading your code. Using deepcopy also means you get to reap the benefits of future optimizations in deepcopy.

First rule of optimization: don't.

deque when to

I have a tree structure of widgets e.g. collection contains models and model contains widgets. I want to copy whole collection, copy.deepcopy is faster in comparison to 'pickle and de-pickle'ing the object but cPickle as being written in C is much faster, so

  1. Why shouldn't I(we) always be using cPickle instead of deepcopy?
  2. Is there any other copy alternative? because pickle is slower then deepcopy but cPickle is faster, so may be a C implementation of deepcopy will be the winner

Sample test code:

import copy
import pickle
import cPickle

class A(object): pass

d = {}
for i in range(1000):
    d[i] = A()

def copy1():
    return copy.deepcopy(d)

def copy2():
    return pickle.loads(pickle.dumps(d, -1))

def copy3():
    return cPickle.loads(cPickle.dumps(d, -1))


>python -m timeit -s "import c" "c.copy1()"
10 loops, best of 3: 46.3 msec per loop

>python -m timeit -s "import c" "c.copy2()"
10 loops, best of 3: 93.3 msec per loop

>python -m timeit -s "import c" "c.copy3()"
100 loops, best of 3: 17.1 msec per loop

Even faster would be to avoid the copy in the first place. You mention that you are doing rendering. Why does it need to copy objects?