Python is entirely different; the two languages cannot be compared with regards to backwards compatibility.
Python has been around since the early 90s, while Go was conceived very recently. Sooner or later, the quirks that resulted from designing the language so long ago had to be addressed, and that's why there's Python 3. The same can be seen in Java and Ruby.
Once Go is used actively for ~9 years (Python 2.0 to 3.0) and suffers no changes that break backwards compatibility, we can compare it with Python.
Python has been around since the early 90s, while Go was conceived very recently. Sooner or later, the quirks that resulted from designing the language so long ago had to be addressed, and that's why there's Python 3. The same can be seen in Java and Ruby.
Once Go is used actively for ~9 years (Python 2.0 to 3.0) and suffers no changes that break backwards compatibility, we can compare it with Python.