Most of those are some old long deprecated things and in general those are all straight up improvements. Python is not my main thing so I'm not really good to answer this, but I listed a few that I am sure triggered errors in some code bases (I'm not saying they are all major). Python's philosophy makes most of those pretty easy to handle, for example instead of foo now you have to be explicit and choose either foo_bar or foo_baz. For example in C there still is a completely bonkers function 'gets' which is deprecated for a long time and it will be there probably for a long time as well. C standard library, Windows C API and Linux C API to large extent are add only, because things should stay bug-to-bug compatible. Python is not like that. This has its perks, but it may cause your old Python code to just not run. It may be easy to modify, but easy is significantly harder than nothing at all.

https://docs.python.org/3/whatsnew/3.3.html#porting-to-pytho...

> Hash randomization is enabled by default. Set the PYTHONHASHSEED environment variable to 0 to disable hash randomization. See also the object.__hash__() method.

https://docs.python.org/3/whatsnew/3.4.html#porting-to-pytho...

> The deprecated urllib.request.Request getter and setter methods add_data, has_data, get_data, get_type, get_host, get_selector, set_proxy, get_origin_req_host, and is_unverifiable have been removed (use direct attribute access instead).

https://docs.python.org/3/whatsnew/3.5.html#porting-to-pytho...

https://docs.python.org/3/whatsnew/3.6.html#removed

> All optional arguments of the dump(), dumps(), load() and loads() functions and JSONEncoder and JSONDecoder class constructors in the json module are now keyword-only. (Contributed by Serhiy Storchaka in bpo-18726.)

https://docs.python.org/3/whatsnew/3.7.html#api-and-feature-...

> Removed support of the exclude argument in tarfile.TarFile.add(). It was deprecated in Python 2.7 and 3.2. Use the filter argument instead.

https://docs.python.org/3/whatsnew/3.8.html#api-and-feature-...

> The function time.clock() has been removed, after having been deprecated since Python 3.3: use time.perf_counter() or time.process_time() instead, depending on your requirements, to have well-defined behavior. (Contributed by Matthias Bussonnier in bpo-36895.)

https://docs.python.org/3/whatsnew/3.9.html#removed

> array.array: tostring() and fromstring() methods have been removed. They were aliases to tobytes() and frombytes(), deprecated since Python 3.2. (Contributed by Victor Stinner in bpo-38916.)

> Methods getchildren() and getiterator() of classes ElementTree and Element in the ElementTree module have been removed. They were deprecated in Python 3.2. Use iter(x) or list(x) instead of x.getchildren() and x.iter() or list(x.iter()) instead of x.getiterator(). (Contributed by Serhiy Storchaka in bpo-36543.)

> The encoding parameter of json.loads() has been removed. As of Python 3.1, it was deprecated and ignored; using it has emitted a DeprecationWarning since Python 3.8. (Contributed by Inada Naoki in bpo-39377)

> The asyncio.Task.current_task() and asyncio.Task.all_tasks() have been removed. They were deprecated since Python 3.7 and you can use asyncio.current_task() and asyncio.all_tasks() instead. (Contributed by Rémi Lapeyre in bpo-40967)

> The unescape() method in the html.parser.HTMLParser class has been removed (it was deprecated since Python 3.4). html.unescape() should be used for converting character references to the corresponding unicode characters.

https://docs.python.org/3/whatsnew/3.10.html#removed

https://docs.python.org/3/whatsnew/3.11.html#removed

https://docs.python.org/3/whatsnew/3.12.html#removed