boto set_contents_from_file from existing boto.s3.key.Key

I'm trying to do something that might not be possible, but is not apparently so in the documentation. Essentially, I want to set the contents of an s3.key.Key using a different s3.key.Key using the set_contents_from_file method. It reports the following error:

 'Key' object has no attribute 'tell'

Here is some code that reproduces the issue.

import boto
from boto.s3.key import Key
s3 = boto.connect_s3()
b = s3.get_bucket("XXXXXX")
ef = b.get_key("figures/test-figure.png") ## this file exists in b.


In [4]: ef.exists()
Out[4]: True


nk = Key(b, "my-new-key.png")
nk.set_contents_from_file(ef)


in set_contents_from_file(self, fp, headers, replace, cb, num_cb, policy, md5, reduced_redundancy, query_args, encrypt_key, size, rewind)
   1222             # programs remain that assume the older auto-rewind interface.
   1223             if not isinstance(fp, KeyFile):
-> 1224                 spos = fp.tell()
   1225                 fp.seek(0, os.SEEK_END)
   1226                 if fp.tell() == spos:

AttributeError: 'Key' object has no attribute 'tell'

I've tried to call: 'ef.open_read()' first, but nothing really seems to affect the behavior. I am using:

boto==2.38.0
botocore==1.2.0