Issue #28317: The disassembler now decodes FORMAT_VALUE argument.

Lib/dis.py

@@ -16,6 +16,8 @@ del _opcodes_all
 _have_code = (types.MethodType, types.FunctionType, types.CodeType,
               classmethod, staticmethod, type)
 
+FORMAT_VALUE = opmap['FORMAT_VALUE']
+
 def _try_compile(source, name):
     """Attempts to compile the given source, first as an expression and
        then as a statement if the first approach fails.
@@ -314,6 +316,13 @@ def _get_instructions_bytes(code, varnames=None, names=None, constants=None,
                 argrepr = argval
             elif op in hasfree:
                 argval, argrepr = _get_name_info(arg, cells)
+            elif op == FORMAT_VALUE:
+                argval = ((None, str, repr, ascii)[arg & 0x3], bool(arg & 0x4))
+                argrepr = ('', 'str', 'repr', 'ascii')[arg & 0x3]
+                if argval[1]:
+                    if argrepr:
+                        argrepr += ', '
+                    argrepr += 'with format'
         yield Instruction(opname[op], op,
                           arg, argval, argrepr,
                           offset, starts_line, is_jump_target)

Lib/test/test_dis.py

@@ -301,6 +301,27 @@ dis_traceback = """\
        TRACEBACK_CODE.co_firstlineno + 4,
        TRACEBACK_CODE.co_firstlineno + 5)
 
+def _fstring(a, b, c, d):
+    return f'{a} {b:4} {c!r} {d!r:4}'
+
+dis_fstring = """\
+%3d           0 LOAD_FAST                0 (a)
+              2 FORMAT_VALUE             0
+              4 LOAD_CONST               1 (' ')
+              6 LOAD_FAST                1 (b)
+              8 LOAD_CONST               2 ('4')
+             10 FORMAT_VALUE             4 (with format)
+             12 LOAD_CONST               1 (' ')
+             14 LOAD_FAST                2 (c)
+             16 FORMAT_VALUE             2 (repr)
+             18 LOAD_CONST               1 (' ')
+             20 LOAD_FAST                3 (d)
+             22 LOAD_CONST               2 ('4')
+             24 FORMAT_VALUE             6 (repr, with format)
+             26 BUILD_STRING             7
+             28 RETURN_VALUE
+""" % (_fstring.__code__.co_firstlineno + 1,)
+
 def _g(x):
     yield x
 
@@ -404,6 +425,9 @@ class DisTests(unittest.TestCase):
         gen_disas = self.get_disassembly(_g(1))  # Disassemble generator itself
         self.assertEqual(gen_disas, gen_func_disas)
 
+    def test_disassemble_fstring(self):
+        self.do_disassembly_test(_fstring, dis_fstring)
+
     def test_dis_none(self):
         try:
             del sys.last_traceback

Misc/NEWS

@@ -62,6 +62,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #28317: The disassembler now decodes FORMAT_VALUE argument.
+
 - Issue #26293: Fixed writing ZIP files that starts not from the start of the
   file.  Offsets in ZIP file now are relative to the start of the archive in
   conforming to the specification.