Recursion error with deep trie on copy()

[pombredanne]

This is unfortunately a well known issue for copy, pickle and json when dealing with nested/recursive data structures. With this:

>>> from pygtrie import Trie
>>> from array import array
>>> t=Trie()
>>> for x in range(100):
...  y = array('h', range(x, 1000)).tostring()
...  t.update([(y,x,)])
... 
>>> t2=t.copy()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
[...]
  File "/home/pombreda/w421/scancode-toolkit-ref/local/lib/python2.7/site-packages/pygtrie.py", line 81, in iterate
    for step, node in sorted(self.children.iteritems()):
RuntimeError: maximum recursion depth exceeded while calling a Python object

There are two ways out IMHO:

1. a custom de/serialization function that flattens the trie (eventually slow)
2. a different non-nested data structure for the Trie such as an array/list-based structure (e.g. double array Trie)

[mina86]

Fixed at HEAD.

[pombredanne]

@mina86 Thank you ++ for this swift fix!