Actually, echo implicitly puts a newline at the end. If you run with echo -n, this is the output:

$ echo -n 'print("a");print("b")' | python3 -m tokenize
1,0-1,5:            NAME           'print'
1,5-1,6:            OP             '('
1,6-1,9:            STRING         '"a"'
1,9-1,10:           OP             ')'
1,10-1,11:          OP             ';'
1,11-1,16:          NAME           'print'
1,16-1,17:          OP             '('
1,17-1,20:          STRING         '"b"'
1,20-1,21:          OP             ')'
2,0-2,0:            ENDMARKER      ''

No newline token present.