Pickle vs. eval for deeply nested objects

[Edward C. Jones]

Here is a little piece of Python that produces a deeply nested tuple:

deep = 'x'
for i in range(50):
     deep = (deep,)

This is a perfectly ordinary Python object. It can be pickled and unpickled:

s = cPickle.dumps(deep)
deep2 = cPickle.loads(s)

But "eval" (and "compiler.parse") fail on "str(deep)" because some stack 
gets too big. Is there some deep reason why cPickle can reconstruct 
"deep" from a string while eval can't?