When I run the following code on Windows/Linux for < Python 3.6, I have no problems.  When I run in Python 3.6.0, I get the subsequent traceback.

I checked the release notes and only saw the following struct module note related to half-floats: Issue #11734

from struct import Struct
import copy
this_fails = Struct('<i')
copy.deepcopy(this_fails)


Traceback (most recent call last):
  File "test_script.py", line 12, in <module>
    copy.deepcopy(this_fails)
  File "F:\Anaconda\envs\py36\lib\copy.py", line 169, in deepcopy
    rv = reductor(4)
TypeError: can't pickle Struct objects


To be clear, I'm copying struct objects as part of a larger class.  As I'm running many function calls where I create the same struct objects, saving the common struct objects allows me to get a factor of 2x speedup on my code.  Deleting the saved struct objects at the end of file reading (and before the deepcopy takes place) fixes the problem.

> When I run the following code on Windows/Linux for < Python 3.6, I have no problems.

You have a problem. Did you try to use the copied object? It is a broken Struct object.

>>> copied = copy.deepcopy(this_fails)
>>> copied.format
>>> copied.size
-1
>>> copied.pack(42)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
struct.error: pack expected -1 items for packing (got 1)
>>> copied.unpack(b'abcd')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
struct.error: unpack requires a bytes object of length -1

Copying Struct object never worked. Now it raises an error rather than silently creating a broken object.

Thank you.

On Wed, Feb 22, 2017 at 9:22 PM, Serhiy Storchaka <report@bugs.python.org>
wrote:

>
> Serhiy Storchaka added the comment:
>
> > When I run the following code on Windows/Linux for < Python 3.6, I have
> no problems.
>
> You have a problem. Did you try to use the copied object? It is a broken
> Struct object.
>
> >>> copied = copy.deepcopy(this_fails)
> >>> copied.format
> >>> copied.size
> -1
> >>> copied.pack(42)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> struct.error: pack expected -1 items for packing (got 1)
> >>> copied.unpack(b'abcd')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> struct.error: unpack requires a bytes object of length -1
>
> Copying Struct object never worked. Now it raises an error rather than
> silently creating a broken object.
>
> ----------
> nosy: +serhiy.storchaka
> resolution:  -> not a bug
> stage:  -> resolved
> status: open -> closed
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue29628>
> _______________________________________
>

As a workaround you can make Struct pickleable:

from struct import Struct
import copy, copyreg
def pickle_struct(s):
    return Struct, (s.format,)

copyreg.pickle(Struct, pickle_struct)

s1 = Struct('<i')
s2 = copy.deepcopy(s1)