The solution is using the string:
"start %ComSpec% /D /S /C \"(\"C:\\Program Files\\Python\\python.exe\" \"$file\" || set /p =Failed execution. Press Enter to exit...) && set /p =Successful execution. Press Enter to exit...\""
The usage of shell_cmd results in starting in background without a visible console window cmd.exe with option /c and the command line specified in next string using the Windows kernel library function CreateProcess with an appropriate filled STARTUPINFO structure.
How the Windows command processor cmd.exe interprets the argument string(s) after the option /c is explained by the help output on running cmd /? in a command prompt window. There are five conditions which define the general behavior on interpreting the argument string(s) after option /c (or option /k) and the first one is the usage of option /S left to option /C or /K.
How the Windows command processor instance is started by Sublime Text 4 on using shell_cmd cannot be controlled by the user. In this case is executed in the background:
C:\Windows\System32\cmd.exe /c start %ComSpec% /D /S /C "("C:\Program Files\Python\python.exe" "$file" || set /p =Failed execution. Press Enter to exit...) && set /p =Successful execution. Press Enter to exit..."
$file is replaced by the file name string by Sublime Text 4 before starting the Windows command processor.
For that reason the command line is coded in a manner to work with cmd.exe /c as used by Sublime Text 4. The free Sysinternals (Microsoft) tool Process Monitor can be used to see what happens in background when an executable starts another executable. After double clicking on a process in log of Process Monitor and selecting tab Process the Command Line can be seen used to start the process.
A visible console window is wanted in this case which is the reason why the internal command start is used to start one more instance of cmd.exe. The usage of start results in using again the function CreateProcess, but this time by the cmd instance started by Sublime Text 4, with using a STARTUPINFO filled to open a new console window by CreateProcess on starting the executable.
The executable to start is cmd.exe specified with its full qualified file name by referencing the value of the predefined Windows environment variable ComSpec with %ComSpec% which is expanded by first started cmd.exe instance already to C:\Windows\System32\cmd.exe on Windows being installed in C:\Windows before executing command start. ComSpec is a system environment variable defined by default with %SystemRoot%\System32\cmd.exe. So it would be also possible to replace %ComSpec% by %SystemRoot%\\System32\\cmd.exe in the command line string.
The second instance of cmd should be started with ignoring the AutoRun registry string value which does not exist by default in Windows registry. That is for security and makes the starting process of second cmd instance a little bit faster. More information about option /D and the AutoRun registry string value can be read in help of Windows command processor output on running cmd /? in a command prompt window.
The option /S is used to explicitly define how the second cmd instance should interpret the argument strings after the next option /C which is for executing a command line and closing cmd after finishing the command line execution.
The command line to execute contains the conditional operators && and || as explained in detail by single line with multiple commands using Windows batch file and twice an equal sign. For that reason it is highly recommended to enclose the entire command line string in " to get these operators and the equal signs interpreted as literal characters by first cmd instance started by Sublime Text 4 when it parses the argument strings after option /c, i.e. the entire coded command line string.
The second cmd instance removes the first and the last " from the argument string after option /C because of option /S and interprets the remaining command line for execution.
In can be read in help of cmd that a file name (or any other argument string) containing a space or one of these characters &()[]{}^=;!'+,`~ (and also <>| not possible in a file name) must be enclosed in " to be interpreted as literal character. C:\Program Files\Python\python.exe contains a space character which is interpreted as argument string separator on not being inside a double quoted argument string. Therefore the full qualified file name of Python executable must be enclosed in " to be interpreted as one argument string and not as the two argument strings C:\Program and Files\Python\python.exe.
The usage of || and && makes it additionally necessary that the execution of Python with the command set executed on python.exe terminating itself with an exit value not equal 0 are combined in a command block by using a pair of ( and ) to get the set command after && executed only if python.exe exited with value 0 for successful execution of the Python script.
For the special requirements caused by using || and && see:
So the second started cmd instance with a visible console window runs the command line:
("C:\Program Files\Python\python.exe" "$file" || set /p =Failed execution. Press Enter to exit...) && set /p =Successful execution. Press Enter to exit...
The cmd instance started first by Sublime Text 4 closes itself already after successful start of second cmd instance by internal command start. In other words the second cmd executes python.exe with CreateProcess with a STARTUPINFO to use the console window and the input, output and error streams of second cmd while first cmd exited itself already which means for Sublime Text 4 that the execution of the tool finished already although in real second cmd.exe and python.exe are still running.
