Arcadiy Ivanov <arca...@ivanov.biz> added the comment:
As an example this is the current state of affairs:
>>> def x():
... foo = "foo"
... s1 = f"S1 value {foo}"
... s2 = f"S2 value {s1}"
... print(s2)
...
>>> dis.dis(x)
2 0 LOAD_CONST 1 ('foo')
2 STORE_FAST 0 (foo)
3 4 LOAD_CONST 2 ('S1 value ')
6 LOAD_FAST 0 (foo)
8 FORMAT_VALUE 0
10 BUILD_STRING 2
12 STORE_FAST 1 (s1)
4 14 LOAD_CONST 3 ('S2 value ')
16 LOAD_FAST 1 (s1)
18 FORMAT_VALUE 0
20 BUILD_STRING 2
22 STORE_FAST 2 (s2)
5 24 LOAD_GLOBAL 0 (print)
26 LOAD_FAST 2 (s2)
28 CALL_FUNCTION 1
30 POP_TOP
32 LOAD_CONST 0 (None)
34 RETURN_VALUE
whereas an fl-string representation of:
>>> def x():
... foo = "foo"
... s1 = fl"S1 value {foo}"
... s2 = fl"S2 value {s1}"
... print(s2)
...
would behave close to:
>>> def x():
... foo = "foo"
... s1 = lambda: f"S1 value {foo}"
... s2 = lambda: f"S2 value {s1()}"
... print(s2())
...
>>> dis.dis(x)
2 0 LOAD_CONST 1 ('foo')
2 STORE_DEREF 0 (foo)
3 4 LOAD_CLOSURE 0 (foo)
6 BUILD_TUPLE 1
8 LOAD_CONST 2 (<code object <lambda> at
0x7ff2ef1abd20, file "<stdin>", line 3>)
10 LOAD_CONST 3 ('x.<locals>.<lambda>')
12 MAKE_FUNCTION 8
14 STORE_DEREF 1 (s1)
4 16 LOAD_CLOSURE 1 (s1)
18 BUILD_TUPLE 1
20 LOAD_CONST 4 (<code object <lambda> at
0x7ff2ef1abae0, file "<stdin>", line 4>)
22 LOAD_CONST 3 ('x.<locals>.<lambda>')
24 MAKE_FUNCTION 8
26 STORE_FAST 0 (s2)
5 28 LOAD_GLOBAL 0 (print)
30 LOAD_FAST 0 (s2)
32 CALL_FUNCTION 0
34 CALL_FUNCTION 1
36 POP_TOP
38 LOAD_CONST 0 (None)
40 RETURN_VALUE
Where LOAD_CONST, LOAD_CONST, MAKE_FUNCTION sequences are replaced with
BUILD_LAZY_STRING (name's provisional) producing the same lambda-like formatter
function that cooperates with FORMAT_VALUE and BUILD_STRING/BUILD_LAZY_STRING
ops.
----------
components: +Interpreter Core -Library (Lib)
nosy: -serhiy.storchaka
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32954>
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