Add functions to return disassembly as string

Lib/test/test_dis.py

 # Minimal tests for dis module
 
 from test.support import run_unittest, captured_stdout
 import difflib
 import unittest
 import sys
 import dis
-import io
 
 class _C:
     def __init__(self, x):
         self.x = x == 1
 
 dis_c_instance_method = """\
  %-4d         0 LOAD_FAST                1 (x)
               3 LOAD_CONST               1 (1)
               6 COMPARE_OP               2 (==)
               9 LOAD_FAST                0 (self)
@@ skipping 148 matching lines @@
              15 INPLACE_ADD
              16 STORE_NAME               0 (x)
              19 JUMP_ABSOLUTE            9
         >>   22 LOAD_CONST               2 (None)
              25 RETURN_VALUE
 """
 
 class DisTests(unittest.TestCase):
 
     def get_disassembly(self, func, lasti=-1, wrapper=True):
-        s = io.StringIO()
-        save_stdout = sys.stdout
-        sys.stdout = s
-        try:
-            if wrapper:
-                dis.dis(func)
-            else:
-                dis.disassemble(func, lasti)
-        finally:
-            sys.stdout = save_stdout
+        if wrapper:
+            s = dis.dis_to_str(func)
+        else:
+            s = dis.disassemble_to_str(func, lasti)
         # Trim trailing blanks (if any).
-        return [line.rstrip() for line in s.getvalue().splitlines()]
+        return [line.rstrip() for line in s.splitlines()]
 
     def get_disassemble_as_string(self, func, lasti=-1):
         return '\n'.join(self.get_disassembly(func, lasti, False))
 
     def do_disassembly_test(self, func, expected):
         lines = self.get_disassembly(func)
         expected = expected.splitlines()
         if expected != lines:
             self.fail(
                 "events did not match expectation:\n" +
@@ skipping 250 matching lines @@
 
     def test_pretty_flags_no_flags(self):
         self.assertEqual(dis.pretty_flags(0), '0x0')
 
 
 def test_main():
     run_unittest(DisTests, CodeInfoTests)
 
 if __name__ == "__main__":
     test_main()