import contextlib
from concurrent import interpreters

assert __name__ == '__main__'

DIV1 = 'v' * 40
DIV2 = '^' * 40

@contextlib.contextmanager
def dump_traceback():
    try:
        yield
    except Exception:
        import traceback
        print()
        print(DIV1)
        traceback.print_exc()
        print(DIV2)

# First try with the current interpreter.
interp0 = interpreters.get_current()
assert interp0 is interpreters.get_main()

# Interpreters "running main" cannot exec or call.
assert interp0.is_running
with dump_traceback():
    try:
        interp0.exec('None')
    except interpreters.InterpreterError as exc:
        if 'running main' not in str(exc):
            raise
with dump_traceback():
    try:
        interp0.call(print, 'spam!', flush=True)
    except interpreters.InterpreterError as exc:
        if 'running main' not in str(exc):
            raise

# prepare_main() should still work
assert 'spam' not in globals()
with dump_traceback():
    interp0.prepare_main(spam=11)
    assert spam == 11

# Try with a subinterpreter
interp1 = interpreters.create()

assert 'q' not in globals()
with dump_traceback():
    interp1.exec("""if True:
        from concurrent import interpreters
        q = interpreters.create_queue()
        interp0 = interpreters.get_main()
        interp0.prepare_main(q=q)
        q.put_nowait(42)
        """)
    assert 'q' in globals()
    val = q.pop()
    assert val == 42