The next Python release is going to be called Python 3 with Python 3 compatibility, which means that it will be compatible with Python 2.7.
This means that users of Python 2 should not have any problems running Python 3 on Linux or Mac OS X, and users of newer versions of Python should not encounter any issues running Python 2 on Windows, macOS, and Linux.
However, users of older versions of the Python interpreter should still experience issues with the interpreter’s built-in version checking.
This is not a bug, but a feature.
Users of older Python versions will be able to run Python 2 with Python 5 compatibility, and those who want to use older versions will have to upgrade to Python 3 to run them on Python 2, as well.
The reason for this is that Python 3 now has an improved, more reliable version checking algorithm.
This makes Python 3 running on Linux and Mac OSX a bit faster than Python 2 running on Windows and Mac.
However: This is a bit misleading.
Python 3 is not backwards compatible.
While Python 3 has improved version checking, it still has a significant amount of problems.
It is a big problem for people who use Python for their daily coding, and it is a problem for developers who use it for debugging and testing their code.
To understand why, we need to look at some of the issues that Python users have faced.
What is the version checking?
Python 3 and Python 2 have different version checking algorithms.
Python 2’s version checking is built-ins.
When Python 3 runs on a machine that has Python 2 installed, Python’s version checker simply compares the operating system version against the system’s version of the standard library.
When the operating systems version is greater than or equal to the system version, the system is assumed to be Python 2 compatible.
If it is less than the system and the operating versions match, then Python 3 will be assumed to have Python 2 compatibility.
This guarantees that if Python 2 is installed on a computer, Python 2 will run on it.
This allows for a number of different kinds of compatibility problems.
For example, the compiler may be unable to correctly link Python 3 compiled programs.
Python will not compile any Python 3 programs compiled by the compiler if the operating environment is incompatible with the system that Python 2 runs on.
When this happens, the resulting program will run in a strange, broken state, even though the program is correctly linked against the correct standard library libraries.
The operating system will still compile the program, but it will not run it.
It will even attempt to link it against a library that is not installed on the system.
These sorts of problems are what the standard compilers are designed to solve.
But the version checkers also have other problems.
The compiler and linker will not always match.
For each version of Python that runs, the two compilers will perform a full comparison.
If one compiles and link to the same file, it will still fail to compile, but the other will not.
In general, the more complete the comparison, the higher the likelihood that the linker and compiler will still find a match.
The more complete your comparison, however, the lower the likelihood of a match, and the more likely the compiler will fail to match.
In addition, the version checks are not always reliable.
A compiler might be unable or unwilling to compile Python 3 or the Python source code.
Even though the operating operating system’s standard library is up to date, the operating computer might not know about it.
The version check may also fail.
If the compiler cannot find a correct match, the compiled program may be impossible to link against.
When that happens, it may be that the operating machine’s version is not up to speed with the version of standard library that the compiler supports.
The running program will still run, but your program will not, and your program’s code may not compile.
This happens to the best of us.
The Operating System Versioning System¶ When running on Python 3 (or Python 2), the operating OS version will be compared against the OS version of version 3.
This will mean that the running program must run on a Linux or Windows system, and may also mean that it must run in the sandboxed mode, which allows the program to access standard libraries.
In a sandboxed environment, you can only link against the version that the system has available for use.
In the operating environments of the most recent operating systems, the sandbox will always be enabled, which is why Python 2 and 3 will run the same program.
However—and this is important—the operating systems OS version does not have to match the version used in the Python 3 interpreter.
If a system does not use Python 2 or 3, then the OS versions of both the interpreter and the compiler are identical.
The same program will compile in the same sandbox.
This also means that the program can access the same standard library code and libraries, but will not be able access