Python yield與實現(xiàn€≤Ω)
yield的(de)功能(néng)類似于return，但(dàn)是(shì)不(bù)同之處在于它返回的(de÷σ>)是(shì)生(shēng)成器(qì)。
生(shēng)成器(qì)
生(shēng)成器(qì)是(shì)通(tōng)過一>₹♥₩(yī)個(gè)或多(duō)個(gè←€σ)yield表達式構成的(de)函數(shù)，每一(y☆∏ ī)個(gè)生(shēng)成器(qì↔Ω)都(dōu)是(shì)一(yī)個(gè)叠代器(qì)（但(dàn)是(∞¥ →shì)叠代器(qì)不(bù)一(yī↑≠)定是(shì)生(shēng)成器(qì)）。
如(rú)果一(yī)個(gè)函數(shùα§)包含yield關鍵字，這(zhè)個(gè)函數(shù)就(jiù)會(huì)變為(" §•wèi)一(yī)個(gè)生(shēng)成器(qì)。
生(shēng)成器(qì)并不(bù)會(huì)一(yī)次返回¥γα所有(yǒu)結果，而是(shì)每次遇到(dào)yield關鍵字後返回相(xiàng)應結果，并保留函數(shù)當前的(de)運行(xφ$φíng)狀态，等待下(xià)一(yī)次的(de)調用(yòn₽←g)。
由于生(shēng)成器(qì)也(yě)是(shì)一(yī)個↓×∞(gè)叠代器(qì)，那(nà)麽它就(jiù)應該支持next方法來(lái)獲取下(xià)一(yī)個(gè)值。 ε
基本操作(zuò)
# 通(tōng)過`yield`來(lái)創建生(≈®↔shēng)成器(qì)
def func():
for™♥✔♦ i in xrang↓÷e(10);
&nbsπ≥÷p; yield&nbsβ¥ p;i
# 通(tōng)過列表來(lái)創建生(shēng)成器(qì)
[i for i&n÷•↕bsp;in xrange(10)]
# 調用(yòng)如(rú)下(xià)
>>> f €∏♣= func()
>>> f&nb∞εsp;# 此時(shí)生(shēng)成器(qì)還(hεái)沒有(yǒu)運行(xíng)
<generator object func at&±♣ nbsp;0x7fe01a853820>
>>> f.next() # 當i★•σ =0時(shí)，遇到(dào)yield關鍵字，直接返回
0
>>> f.next() # 繼續上(s£φhàng)一(yī)次執行(xíng)的(de)位置，進入下(xià)✔™∏一(yī)層循環
1
...
>>> f.next(±βαε)
9
>>> f.next✔♥↔() # 當執行(xíng)完最後一✔₽₩(yī)次循環後，結束yield語句，生(s<∑hēng)成StopIteration異常
Traceback (most r≥ ecent call last):
File "<stdiα✔<€n>", line•÷" 1, in <Ω↑;module>
StopIteration
>>>
除了(le)next函數(shù)，生(sα•hēng)成器(qì)還(hái)支持send函數(shù)。✔ ®Ω該函數(shù)可(kě)以向生(shēng)成器(qì)傳遞參 αα數(shù)。
>>> def f↓φunc():
... &nb♠'sp;n = 0
... &♠nbsp; while 1:
... ♠§∑ &nbs§'p; n ∏<σ;= yield n #可(kě≈>§)以通(tōng)過send函數(shù)向n賦值δδ≈
...
>>> f ∏ε'= func()
>>> f.next() ¥$≤δ;# 默認情況下(xià)n為(wèi)0
0
>>> f.≤δ<send(1) #n賦值1
1
>>> f.send(→↓★2)
2
>>>
應用(yòng)
最經典的(de)例子(zǐ)，生(shēng)成無限序列。
常規的(de)解決方法是(shì)，生(shēng)←₹♦成一(yī)個(gè)滿足要(yào)求的(de)很(hěn)大(dà)的α↕≈"(de)列表，這(zhè)個(gè)列表需要(yào)保存在內(nè&®i)存中，很(hěn)明(míng)顯內(nèi)存限♦÷≠σ制(zhì)了(le)這(zhè)個(gè)問(wèn"§)題。
def get_primes(start):
for&nε™'bsp;element in mβ±€agical_infinite_range(±©♠ start):
₹✘&'; if is_p♥♣rime(element):
&nb≥ ∑sp; &nbs☆₹p;return element
如(rú)果使用(yòng)生(shēng)成器(qì)就(jiù)↕>不(bù)需要(yào)返回整個(gè)列表，每次都(dōu)隻是(shì>₹)返回一(yī)個(gè)數(shù)據，避免了(le)內(nèi)存的(≠←de)限制(zhì)問(wèn)題。
def get_primes(number):
whil•♠©e True:
&nbs"λ★ p; if is_prime(numbe↔₹r):
←€>; &nb♠∏♥φsp; yield number
&n≤ <☆bsp; number += 1
生(shēng)成器(qì)源碼分(fē∞→n)析
生(shēng)成器(qì)的(de)源δ 碼在Objects/genobject.c。
調用(yòng)棧
在解釋生(shēng)成器(qì)之前，需要×&(yào)講解一(yī)下(xià)Pythoγ☆ Ωn虛拟機(jī)的(de)調用(yòng)原理(lǐ)。
Python虛拟機(jī)有(yǒu)一(yī)個(gè)棧幀的(←γ∑de)調用(yòng)棧，其中棧幀的(de)是(shì)PyFrameObject，位于Include/frameobject.h。
typedef struct _frame&nbε★γφsp;{
PyObject_VAR_HEπ ®±AD
struct&n±γbsp;_frame *f_back; ↑± /* previous frame, or£∑ NULL */
PyCod¶∑eObject *f_code; &nbγ₹≥↔sp; /* code segm♠♣☆ent */
&nb∑ ↔sp;PyObject *f_builtin≥φs; /* ₽₹builtin symbol table (PyDictObject¶↕) */
PyObject♠€ *f_globals; &nbs©→€p;/* global symbol table (€αPyDictObject) */
Pyλ₹≠Object *f_locals; &nbs↑γ®±p; /* loc§♣al symbol table (any mapping) *↔/
PyObject **fβ ≠®_valuestack; &n ≤✔bsp; /* p>€δoints after the last local */
γ♦≈φ;/* Next free slot in f_valuestack.&nb÷♠↔sp; Frame creation sets to f_v>↓aluestack.
↔∑✘; Frame evaluat€±ion usually NULLs it, bu₩←t a frame that yields sets it
&nbsπ≠'p; to the current stacσ$✔k top. */
&nb©♦±sp;PyObject **f_stacktop;
PyObject *f_ ©≤trace; &nb✘σsp; /* Trace function */
/* If a∏≤n exception is raised in this frame,σ>♣∏ the next three are used to
* record the ₹ exception info (if any) originally λβin the thread state.&nbs&ε±p; See
* c∏♣→∏omments before set_exc_i"nfo() -- it's noσt obvious.
÷✔φ±* Invariant: &nbs$Ω♣©p;if _type is NULL, th"∞≤en so are _value and _t₩♣ raceback.
*γφ Desired invariant:&•≤nbsp; all three are NULγ♣₹L, or all three are non-NULL.&∏→♦nbsp; That
&nb≠™β♦sp; * one isn't currently true™¥✘, but "should bΩ™e".
&nbs®∏™p; */
PyObje₹±↕ct *f_exc_type, ∏Ω®;*f_exc_value, *f_exc_traceback;
&n≤←™bsp;PyThreadState *f↔₩'_tstate;
int f≥₽<≠_lasti; &₩§nbsp; ✘δ;/* Last instruction if cα✔alled */
/* Ca"©φ÷ll PyFrame_GetLineNumber() ÷' instead of reading this field×♦↔≈
&nbs∏©φp; directly. Asπ≤ of 2.3 f_lineno is only valid wφβαλhen tracing is
&↓φ↕♠nbsp; active (i.e. when f_trace i∞© ↕s set). At other times w★'ε¶e use
&↓φ≠nbsp; PyCode_Addr2L♣γ↑ine to calculate the line from t≠↔®he current
↔×; bytecode index. */
int f_linφeno; ≠σ; /* Current line"∞←≈ number */
int f_iblo•∞™♥ck; ☆δβ; /* index in fΩγ"®_blockstack */
PyTr€£♦yBlock f_blocksta©§ck[CO_MAXBLOCKS];&nb∑λ✘¶sp;/* for try and loop blocks */
PyObject *f_lφ®ocalsplus[1]; /♥奩* locals+stack, dynamically sizeσ♥d */
} PyFrameObject;
棧幀保存了(le)給出代碼的(de)的(de)信息和(hé)上(shàn™"g)下(xià)文(wén)，其中包含最後執行(xíng)的(>₩<φde)指令，全局和(hé)局部命名空(kōng)間(jiān)，異常狀态等信£♣σ息。f_valueblock保存了(le)數(shù)據，b_blockstack保存了(le)異常和(hé)循環控制(zhì)方₩γ₩∑法。
舉一(yī)個(gè)例子(zǐ)來(lái)說(shuō)明(míng)，"•
def foo():
&nbs♣γ>p;x = 1
deπβf bar(y):
&♥nbsp; z =&nbΩ<±sp;y + 2 ×₽γ≈#
那(nà)麽，相(xiàng)應的(de)調用(yòng)棧如δ↓(rú)下(xià)，一(yī)個(gè)py文(wén)件(jiàn)，ε&©一(yī)個(gè)類，一(yī)個(gè)函數(shù)都(dōu)是↑₹(shì)一(yī)個(gè)代碼塊，對(duì)應者一©✘(yī)個(gè)Frame，保存著(zhe)上(s>εhàng)下(xià)文(wén)環境以及字節碼指令。
c --------------←∏-------------
a | bar F§rame ₩ ¶★ β× | -> bloc"™αk stack: []
l | &nbs ≥€p; (newest) &nb¥≈sp; &n≈εbsp; &n✘bsp;| -> data&n∑α•£bsp;stack: [1, 2]
l ------------------¥✔ε∞---------
| foo Frame&nbsλ★p; δ¥ &↕✘nbsp; | -&→♠gt; block stack: []
s | &ε♣φnbsp; ✔α↕ &n÷γbsp; ¥♦ &↕≥nbsp; | -> data stack:&£ [.bar at 0δ<x10d389680>, ≤λ;1]
t -------♣α>--------------------
a | m↔γ♣ain (module) Ω♠¥Frame §σ₽; | -> blo→♠↓★ck stack: []
c | &☆φ™nbsp; (oldest) &n✘ bsp; &₩¥↑nbsp; &nb÷✘sp; | -> data&nb"₩sp;stack: []
k -----------------♣§----------
每一(yī)個(gè)棧幀都(dōu)擁有(yǒu)自(zì)≤✘ε己的(de)數(shù)據棧和(hé)block棧，獨立的(♣γde)數(shù)據棧和(hé)block棧使得(÷✘↓λde)解釋器(qì)可(kě)以中斷和(hé)恢複棧幀（生(shēnεεπg)成器(qì)正式利用(yòng)這(zhè✘φ)點）。
Python代碼首先被編譯為(wèi)字節碼，再由Python£÷✔>虛拟機(jī)來(lái)執行(xíng)。一(yī)般來(lái)說(sλ∏huō)，一(yī)條Python語句對×Ω≥✔(duì)應著(zhe)多(duō)條字節碼（由于每條字節碼≠¶對(duì)應著(zhe)一(yī)條C語句，而不(bù)是(φε→shì)一(yī)個(gè)機(jī)器(qì)指令，所以不(bù)能£♦(néng)按照(zhào)字節碼的(de)數(s≤↕¶hù)量來(lái)判斷代碼性能(néng)）。✔≠Ω
調用(yòng)dis模塊可(kě)以分(fēn)析字節碼，
from dis import dis
dis(foo)
5 & ☆↓✘nbsp; §>™←; 0&nbsΩ≥p;LOAD_CONST &nbs>≈ p; ♥&<; ™ &nbs&δβp;1 (1) # 加載→↓常量1
&n ±bsp; &nbδ₹≈sp; &nb>↔sp; 3 STORE_FAST&n☆bsp; &nbs¶∞★p; ←©₹ 0 (>★₹x) # x賦值為(wèi)1
6 ∞γ₩ ↑♥Ωβ 6 LOA♥♦D_CONST ♦"; &n®∏"bsp; 2 (<£ε';code>) # 加載常量2
&nb✔≠÷sp; &nb >sp; 9 MAKE_FUNCTION&nbδ↓Ω&sp; &∏★★nbsp; &nbβ¶✔sp; 0 # 創建函數(φ¶shù)
& '✘←nbsp; &™♣nbsp; 12 STORE_FAST↔∞ ₩σ∞♣; &nbsγ€p; &n$♥ ™bsp; 1 (bar ¥¶∑)
9 &nb÷×♣§sp; ¶♦>©; 15&nb ♠sp;LOAD_FAST &nb×γ×sp; &nb•✘sp; &nb™≠ sp; 1&nbsσΩp;(bar)
&nb>¥←<sp; $☆™ 18 LOAD_↔ FAST &nb®φ≤∏sp; &∑™nbsp; ♣ 0 (x)
₹¶; &nb<™sp; 21 CALL_FUNλ ✘CTION ÷ ♠ &n♦¥bsp; 1 # ₽≠ 調用(yòng)函數(shù)
&↑¥§nbsp; &n♠≥♦bsp;24 RETURN_VALUE ™β &nb<π ÷sp; </code><↑
其中，
第一(yī)行(xíng)為(wèi)代碼行(xí∏εng)号；
第二行(xíng)為(wèi)偏移地(dì)址；
第三行(xíng)為(wèi)字節碼指令；
第四行(xíng)為(wèi)指令參數(±∏∞™shù)；
第五行(xíng)為(wèi)參數(shù)解釋。
生(shēng)成器(qì)源碼分(fēn)析
由了(le)上(shàng)面對(duì)于調用(yòng)棧的(de✔→ ∞)理(lǐ)解，就(jiù)可(kě)以很(hěn)容<£¶易的(de)明(míng)白(bái)生(shēng)成器(qì≤←≠¥)的(de)具體(tǐ)實現(xiàn)。
生(shēng)成器(qì)的(de)源碼位于↑ object/genobject.c。
生(shēng)成器(qì)的(de)創建
PyObject *
PyGen_New(PyFrameObjecφ€φβt *f)
{
PyG±✔enObject *gen = PyObject_GC↕™♣_New(PyGenObject, &PyGen_Ty♠&pe); # 創建生(shēng)成♦¶器(qì)對(duì)象
if ±;(gen == NULL) ₹÷{
& "♣≤nbsp; Py_DECREF(f);
∑←¶σ return NULL→Ω;
}
gen->gi_↕>πframe = f;&n♣☆®↓bsp;# 賦予代碼塊
Py↔♥σ'_INCREF(f->f_code); # 引用(yòng↓¥)計(jì)數(shù)+1
gen-♦§>gi_code = (PyObjec §₹®t *)(f->f_code);
gen->g•δ₩♣i_running = 0; # 0表示為(wèπβ®i)執行(xíng)，也(yě)就(jiù)是≈§(shì)生(shēng)成器(qì)的(de)初始狀态
gen-&♥'♣gt;gi_weakreflist =&nbs♠p;NULL;
_PyObject_GC_TR®α♥ACK(gen); # GC跟蹤
re♥γλturn (PyObject *☆"'≥)gen;
}
send與next
next與send函數(shù)，如(rú)下(xià)
static PyObject *
gen_iternext(PyGenObδ✘πject *gen)
{
return&n©γφbsp;gen_send_ex(gen, NULL, ≥₩↔₹0);
}
static PyObject *
gen_send(PyGenObject *gen, Py♦®$✘Object *arg)
{
retγα♥urn gen_send_ex(gen, arg,&n®♠bsp;0);
}
從(cóng)上(shàng)面的(de)代碼中可(kě)÷©♣™以看(kàn)到(dào)，send和(hé)next都(dōu)是(shì)調用(yòng)的(de)同一☆₹(yī)函數(shù)gen_send_ex，區(qū)别在于是(shì)否帶有(yǒu)參數(shù)。
static PyObject *
gen_send_ex(PyGenObject *gen, ₹♥;PyObject *arg, int eσ₽xc)
{
PyThreadSt←ate *tstate = PyTh≥★readState_GET();
&∏→≈;PyFrameObject *f =$♠♦× gen->gi_frame;
P✔$€≠yObject *result;
i♠ &f (gen->gi_runni↓♣<ng) { # 判斷生(shēng≈☆δ)成器(qì)是(shì)否已經運行(xíng)
£ ≤; PyErr_SetString(↔'Ω☆PyExc_ValueError,
&nbs>₩ ✘p; &nb€←sp; &nbs§£☆←p; &nbsδδ™p; &nb&§γsp; "generator already ex§∑ecuting");
&nbφ¥sp; retur'←δn NULL;
∞}
•§α;if (f==NULL £;|| f->f_stack≠top == NULL)☆δ↔✔ { # 如(rú)果代碼塊為(≤∑&wèi)空(kōng)或調用(yòng)棧為(wè&±i)空(kōng)，則抛出StopIteration異常
&nbs∏↕↑→p; /* Only set excepti €on if called from send() */
$ ; if (argδε÷ && !exc)
&n¶↑bsp; ™₽♣•; PyErr_SetNone(PyExc_StopItera↕ ↔πtion);
&nb€±∏♦sp; return NULL;€♠
}
if ↔"(f->f_lasti == -1) { £≤♦;# f_lasti=1 代表首次執行(xíng)
&nσ€bsp; &↓∞nbsp;if (arg&nbsπ<₹p;&& arg != P"εy_None) { # 首次←↔執行(xíng)不(bù)允許帶有(yǒu)參數(shù)
&nb$☆¶εsp; &n$≠γbsp; PyErr_SetString(PyExc_TypeEr← ror,
εφ ; ✔Ω♠ &™ ₹♣nbsp; &nbs®< ♥p; €≤∞;"can't send non-None v'×≤₹alue to a "
§•σα &nφ✔bsp; >©; &nbs™≈ →p; &nbs♥≤☆p; & ♥nbsp;"just-started generator&quo•γεt;);
&nbδ€ sp; ☆ ret÷Ω<urn NULL;
&nbε↕sp; }
} else&nb ±↑sp;{
&n±★±bsp; /* Push arg onto♣₹ ★ the frame's value stack≠> */
←₩♣★ result =&nbs♥'÷§p;arg ? arg&nbsΩ↕₹p;: Py_None;
&nb€↔ sp; Py_"∏INCREF(result); # 該參數(shù)引用(¥≥ yòng)計(jì)數(shù)+1
&nb≥>₩sp; *(f-&g♣&t;f_stacktop++) = r×∑esult; # 參數(shù)壓棧
}
π₽/* Generators always return to ¶α"their most recent caller, not
*≤→∞ necessarily their creato'$↓♦r. */
f->f_tstate&€ = tstate;
Py_XINCα₩¶REF(tstate->frame);
assert(f-&$₽ φgt;f_back == NULL);
&nbsδ ≠p;f->f_back = tstate-&g $γt;frame;
gen->Ω×;gi_running =&n♣↕♥bsp;1; # 修改生(shēng)成器(qì)執行(x→€£íng)狀态
result ♠≈σ= PyEval_EvalFrameEx(f,&φ÷ $nbsp;exc); # 執行(xíng)字節碼
gen✘ ↑->gi_running = 0; #←✔ 恢複為(wèi)未執行(xíng)狀态
/* Don't¶♦ keep the reference to f_bac™✔®∞k any longer than necessary. &n£ ♦∞bsp;It
βδ * may keep a chain of frames al©×ive or it could create a reference
* cycle. ε<♣©*/
assert(f-$↕₩>f_back == tstat×γe->frame);
Py_CLE✘₩AR(f->f_back);
/* Clear the"÷®∑ borrowed reference tφ★♦™o the thread state */
f->f_tstate≤✔↓ = NULL;
/* If•π the generator just returned (as oppos<ed to yielding), signal
* that the∑×φ¶ generator is exhaust≠♦®→ed. */
if&nb₽£↕≥sp;(result == Py_↓≠None &&&nb×∑≥sp;f->f_stacktop ==&nbs>✘"p;NULL) {
&nbs∞γp; Py_DECREF(r↔←♠esult);
₹≥≠; result = NU≈™÷LL;
&n←≤↕bsp; /* Set exception if noπ∏t called by gen_iternext() */
&nbs&α™πp; iπ∏☆f (arg)
✘< ₩₹♠; PyErr_SetNone(PyExc_St"¶opIteration);
}
if&nbλ¥↑sp;(!result || f₹φ£->f_stacktop == NULL)&nbsεΩ↔p;{
&nbε₩πsp; /* generator can't ∏ be rerun, so release the fra♥↓♣me */
&nε•π∑bsp; Py∞≤ _DECREF(f);
&n←'σ bsp; gen->gi_££"frame = NULL;
&n¶"σbsp;}
★;return result;
}
字節碼的(de)執行(xíng)
PyEval_EvalFrameEx函數(shù)的(de)功能(néng)為(wèi)執行(xíng)字節↕≈碼并返回結果。
# 主要(yào)流程如(rú)下(xià)，
for (;;) {
switch(opcγ£ode) { # opcodeπ•™為(wèi)操作(zuò)碼，對(duì)應著(zhe)↔$各種操作(zuò)
&n¥→α♦bsp; &nbs p;case NOP:
★∞★π &nbγ↔✘sp; ©★£;goto fast_next_opcode; ←≥
&nbβ×sp; ...
® ...
&n∏£bsp; cas∏e YIELD_VALUE: # 如↓£(rú)果操作(zuò)碼是(shì)yield
&n♥≈bsp; &n≠&bsp; retval = POγ↑P();
∞§Ω☆ >↑ε£;f->f_stacktop €♣;= stack_pointer;
&★£nbsp; &nbs &≤p; why =&nb₽÷>Ωsp;WHY_YIELD;
$< &β←nbsp; goto fas± §t_yield; # 利用(yòng)goto§>σ↔跳(tiào)出循環
}
}
fast_yield:
..¥Ω.
return vetval; # 返←★↑回結果
舉一(yī)個(gè)例子(zǐ)，f_×±$back上(shàng)一(yī)個(gè)Frame，f_lasti上(☆&shàng)一(yī)次執行(xíng)的(de)指令的(de)偏移量，
import sys
from dis import dis
def func():
fλ™β↕ = sys._getf✔∞©♦rame(0)
pσ<™rint f.f_lasti
pri§₽Ωnt f.f_back
yield&nbs↕p;1
print f.f↑↑_lasti
print $;f.f_back
yield&nδ®'βbsp;2
a = func()
dis(func)
a.next()
a.next()
結果如(rú)下(xià)，其中第三行(xí♠'"ng)的(de)英文(wén)為(wèi)操作(zu↓ '>ò)碼，對(duì)應著(zhe)上(sh↓Ω<àng)面的(de)opcode，每次switch✔"♦←都(dōu)是(shì)在不(bù)同的(de)opcode之間(♠∏jiān)進行(xíng)選擇。
6 &n&λ↓bsp; &n"✔↓bsp;0 LOAD_GLOBAL&n±β£↕bsp; ÷" φ↑ 0 (s♦≥ys)
÷α &nb↑"sp; 3 LOAD_ATTR&nb§π§sp; ♥→; ₹✘®∑; &nα₹±×bsp; 1 (_getfr§>≤εame)
γ→; &nbs®☆βp; &"₩nbsp;6 LOAD_CONST &nb♣×sp; ∑★ &nσ♣™§bsp; 1 (0)
&nbsπεp; &n≈¥bsp; &nbs&↑p;9 CALL_FUNCTION ≠€<; ↕ ∏; >☆§;1
&n↕♦εbsp; © →×; 12 STO←≤<¥RE_FAST ±£π; &nb÷÷≤sp; &nbsγ "p; 0 (f)
7 &<Ω↑nbsp; &nbs'₽₩p; 15 LOAD_FAST &n∏' 'bsp; &n✘£bsp; &nb∑₹$∏sp; 0&✔✘nbsp;(f)
• ; &nbs↑ p; 18 LOA₹D_ATTR &nbs∏✘×p; • φ≠; 2 (f_lasti)
&n> ¶bsp; &•≥εnbsp; 21&nbδγ★πsp;PRINT_ITEM &±nbsp; &nβα&∏bsp;
&nbsλp; ≠↕© 22 P©Ω≥'RINT_NEWLINE ∏✔∑
8 ∞>™✔ ∏→23 LOAD_FAST & ♥nbsp; &nbs"p; &nbs♠× p; 0 (f)
&n★ ±αbsp; &nbs↓±πp; 26&¥σφnbsp;LOAD_ATTR &nb÷>sp; &φ₩÷←nbsp; &ε★≥nbsp; &nbsπ¶☆p;3 (f_back)
→₽÷π; &nbs₽☆p; 29&nελ¶bsp;PRINT_ITEM &n★✔'bsp; &n®≈♠✘bsp;
& ∞↓nbsp; &nb₹₩φ→sp; 30 PRI↓©NT_NEWLINE &nbs☆&™p;
9 &φσnbsp; ≠∏31 LOAD_CONST &✘•₹∏nbsp; &₩εnbsp; &nb♥Ω₽γsp; 2 (1)
&nbs<✔p; &π$↓£nbsp; 34&nbs∑→βp;YIELD_VALUE &nbγγ sp; # 此時(shí)操作(zuò)αα碼為(wèi)YIELD_VALUE，直接跳(tiào)轉上(shàng)述g←α&☆oto語句，此時(shí)f_lasti為(wèi)當前∑★¥指令，f_back為(wèi)當前frame
✘>'✔; &nbβ↑sp; 35 POP_TOP •ε &n↕≤bsp; ≤$;
11 γ; 3Ω↔6 LOAD_FAST &nb↕↑Ω↕sp; &∞≠♦$nbsp; &nb≤ sp; >φ•₩;0 (f)
ε♥; ↓ 39 LOAD_ATTR Ω₹ &nb♦₹'sp; €→; &nb∏>×→sp;2 (f_lasti)
®₽∞Ω &n•₩∞ bsp; 42 PRINT_ITε→§EM &nb>γsp; ∏¥σ¶
&nb≥∞↔sp; $δ♣≤; 43 P' ↔RINT_NEWLINE &nb♦'♣ sp;
12 &nb←§'sp; &nbβ↕sp; 44 LOAD_λ✔♦≤FAST &nbs÷✔•p; &₹↔nbsp; ≤≈ 0 (f)
&nbε♠↔sp; &ασnbsp; &★πnbsp;47 LOAD_ATTR ©₽π &nb♣≤≈sp; ♦; ↕♥♦∑; 3 (f_back)
& φ nbsp; &n$γ bsp; 50 PRINT_ITΩβEM &nbs>÷p; &nb∑>±↕sp;
&nbsε§ p; Ω♦✘∑ 51 ✘↓λPRINT_NEWLINE ♥¥₹
13 &₽<<nbsp; 5¶γ•∑2 LOAD_CONST &♣₩♣nbsp; &nbsφ↔÷↕p; 3 λ (2)
®™≠₩; ↕☆✔; 55 YIELD_VALUE&nbs™₽✔p; ®
&₩₽nbsp; &¶&∑§nbsp; 56 POP_Tδ&OP &n>©™bsp; β<'; &∞"πnbsp;
&nb∏±sp; &nαα♣αbsp; 57 LOAD_CON™λ'ST ®♥ ; ®♣∑♦; &¶¶®nbsp; 0 (None•↕↑$)
¥™±δ; &±; 60 RETURN_VALUE '∑₽ &nbs≠÷p;
18
<frame object at&nbπ∞sp;0x7fa75fcebc20>&nb ←₹sp;#和(hé)下(xià)面的(de)frame相(xiàng)同，屬于同∏ €一(yī)個(gè)frame，也(yě)就(jiù)是(shì)說(shu∞¥ō)在同一(yī)個(gè)函數(shù)（命δ$♠≠名空(kōng)間(jiān)）內(nèi)，frame是(shì)↑÷同一(yī)個(gè)。
39
<frame object a→'≤&t 0x7fa75fcebc20>
來(lái)源： cococo點點
http://www.cnblogs.com/cod↑÷er2012/p/4990834.html
