what is deepcopy's second parameter does,
<pre><code>from copy import* 
a=[1,2,3,4]
c={'a':'aaa'}
print c
#{'a': 'aaa'}
b=deepcopy(a,c)
print b

print c
# print {'a': 'aaa', 10310992: 3, 10310980: 4, 10311016: 1, 11588784: [1, 2, 3, 4, [1, 2, 3, 4]], 11566456: [1, 2, 3, 4], 10311004: 2}
</code></pre>

<p>why c print that</p>

<p>Please try to use the code, rather than text, because my English is not very good, thank you</p>

<p>in django.utils.tree.py</p>

<pre><code>def __deepcopy__(self, memodict):
        """
        Utility method used by copy.deepcopy().
        """
        obj = Node(connector=self.connector, negated=self.negated)
        obj.__class__ = self.__class__
        obj.children = deepcopy(self.children, memodict)
        obj.subtree_parents = deepcopy(self.subtree_parents, memodict)
        return obj



import copy
memo = {}
x1 = range(5)
x2=range(6,9)
x3=[2,3,4,11]
y1 = copy.deepcopy(x1, memo)
y2=copy.deepcopy(x2, memo)
y3=copy.deepcopy(x3,memo)
print memo
print id(y1),id(y2),id(y3)
y1[0]='www'
print y1,y2,y3
print memo
</code></pre>

<p>print :</p>

<pre><code>{10310992: 3, 10310980: 4, 10311016: 1, 11588784: [0, 1, 2, 3, 4, [0, 1, 2, 3, 4]], 10311028: 0, 11566456: [0, 1, 2, 3, 4], 10311004: 2}
{11572448: [6, 7, 8], 10310992: 3, 10310980: 4, 10311016: 1, 11572368: [2, 3, 4, 11], 10310956: 6, 10310896: 11, 10310944: 7, 11588784: [0, 1, 2, 3, 4, [0, 1, 2, 3, 4], 6, 7, 8, [6, 7, 8], 11, [2, 3, 4, 11]], 10311028: 0, 11566456: [0, 1, 2, 3, 4], 10310932: 8, 10311004: 2}
11572408 11581280 11580960
['www', 1, 2, 3, 4] [6, 7, 8] [2, 3, 4, 11]
{11572448: [6, 7, 8], 10310992: 3, 10310980: 4, 10311016: 1, 11572368: [2, 3, 4, 11], 10310956: 6, 10310896: 11, 10310944: 7, 11588784: [0, 1, 2, 3, 4, [0, 1, 2, 3, 4], 6, 7, 8, [6, 7, 8], 11, [2, 3, 4, 11]], 10311028: 0, 11566456: ['www', 1, 2, 3, 4], 10310932: 8, 10311004: 2}
</code></pre>
