Compile and run some source in the interpreter.
Arguments are the same as for compile_command(); the
default for filename is '<input>', and for
symbol is 'single'. One several things can happen:
The input is incorrect; compile_command() raised an
exception (SyntaxError or OverflowError). A
syntax traceback will be printed by calling the
showsyntaxerror() method. runsource() returns
0.
The input is incomplete, and more input is required;
compile_command() returned None.
runsource() returns 1.
The input is complete; compile_command() returned a code
object. The code is executed by calling the runcode() (which
also handles run-time exceptions, except for SystemExit).
runsource() returns 0.
The return value can be used to decide whether to use
sys.ps1 or sys.ps2 to prompt the next line.
Execute a code object.
When an exception occurs, showtraceback() is called to
display a traceback. All exceptions are caught except
SystemExit, which is allowed to propagate.
A note about KeyboardInterrupt: this exception may occur
elsewhere in this code, and may not always be caught. The caller
should be prepared to deal with it.
Display the syntax error that just occurred. This does not display
a stack trace because there isn't one for syntax errors.
If filename is given, it is stuffed into the exception instead
of the default filename provided by Python's parser, because it
always uses '<string>' when reading from a string.
The output is written by the write() method.
Display the exception that just occurred. We remove the first stack
item because it is within the interpreter object implementation.
The output is written by the write() method.