With the benefit of hindsight, though, Python 3 could have been done as a non-breaking upgrade.

Imagine if the same interpreter supported both Python 3 and Python 2. Python 3 code could import a Python 2 module, or vice versa. Codebases could migrate somewhat more incrementally. Python 2 code's idea of a "string" would be bytes, and python 3's idea of a "string" would be unicode, but both can speak the other's language, they just have different names for things, so you can migrate.

That split between bytes and unicode made better code. Bytes are what you get from the network. Is it a PNG? A paragraph of text? Who knows! But in Python 2, you treated them both as the same thing: a series of bytes.

Being more or less forced to decode that series into a string of text where appropriate made a huge number of bugs vanish. Oops, forget to run `value=incoming_data.decode()` before passing incoming data to a function that expects a string, not a series of bytes? Boom! Thing is, it was always broken, but now it's visibly broken. And there was no more having to remember if you'd already .decode()d a value or whether you still needed to, because the end result isn't the same datatype anymore. It was so annoying to have an internal function in a webserver, and the old sloppiness meant that sometimes you were calling it with decoded strings and sometimes the raw bytes coming in over the wire, so sometimes it processed non-ASCII characters incorrectly, and if you tried to fix it by making it decode passed-in values, it start started breaking previously-working callers. Ugh, what a mess!

I hated the schism for about the first month because it broke a lot of my old, crappy code. Well, it didn't actually. It just forced me to be aware of my old, crappy code, and do the hard, non-automatable work of actually fixing it. The end result was far better than what I'd started with.

> With the benefit of hindsight, though, Python 3 could have been done as a non-breaking upgrade.

Not without enormous and unnecessary pain.