@@ -253,4 +253,160 @@ static PyStringObject *characters[UCHAR_MAX + 1];
253253
254254## 修改代码测试
255255
256- 好像 characters 不会缓冲'* '之类的特殊字符。
256+ 好像 characters 不会缓冲'* '之类的特殊字符。
257+ 258+ ** 更新:**
259+ 关于这个问题我在 CPyUG发过[ 帖子] ( https://groups.google.com/forum/?hl=zh-CN#!topic/python-cn/Oszno8oGAXQ ) 。经过更多的测试,把我的发现记录一下。
260+ 261+ 262+ - 通过Python shell测试和使用Python执行脚本文件进行测试的结果不一致,下面是两者的测试结果
263+ 264+ 使用 `len('?')` 打印出 characters 中不为 NULL 的元素。
265+ 266+ Python shell
267+ 268+ ```python
269+ >>> len('?')
270+ value: /(47), refcnt: 12
271+ value: 1(49), refcnt: 2
272+ value: E(69), refcnt: 1
273+ value: F(70), refcnt: 1
274+ value: N(78), refcnt: 1
275+ value: O(79), refcnt: 1
276+ value: R(82), refcnt: 1
277+ value: T(84), refcnt: 1
278+ value: W(87), refcnt: 1
279+ value: X(88), refcnt: 1
280+ value: _(95), refcnt: 7
281+ value: a(97), refcnt: 3
282+ value: c(99), refcnt: 4
283+ value: d(100), refcnt: 3
284+ value: e(101), refcnt: 2
285+ value: f(102), refcnt: 2
286+ value: g(103), refcnt: 1
287+ value: i(105), refcnt: 10
288+ value: k(107), refcnt: 8
289+ value: l(108), refcnt: 1
290+ value: m(109), refcnt: 6
291+ value: n(110), refcnt: 4
292+ value: o(111), refcnt: 1
293+ value: p(112), refcnt: 7
294+ value: r(114), refcnt: 2
295+ value: s(115), refcnt: 6
296+ value: t(116), refcnt: 4
297+ value: u(117), refcnt: 1
298+ value: w(119), refcnt: 3
299+ ```
300+ 301+ python t.py
302+ 303+ ```python
304+ # t.py
305+ len('?')
306+ 307+ # 输出结果
308+ value: /(47), refcnt: 12
309+ value: 1(49), refcnt: 2
310+ value: ?(63), refcnt: 4
311+ value: E(69), refcnt: 1
312+ value: F(70), refcnt: 1
313+ value: N(78), refcnt: 1
314+ value: O(79), refcnt: 1
315+ value: R(82), refcnt: 1
316+ value: T(84), refcnt: 1
317+ value: W(87), refcnt: 1
318+ value: X(88), refcnt: 1
319+ value: _(95), refcnt: 7
320+ value: a(97), refcnt: 3
321+ value: c(99), refcnt: 4
322+ value: d(100), refcnt: 3
323+ value: e(101), refcnt: 2
324+ value: f(102), refcnt: 2
325+ value: g(103), refcnt: 1
326+ value: i(105), refcnt: 10
327+ value: k(107), refcnt: 8
328+ value: l(108), refcnt: 1
329+ value: m(109), refcnt: 6
330+ value: n(110), refcnt: 4
331+ value: o(111), refcnt: 1
332+ value: p(112), refcnt: 7
333+ value: r(114), refcnt: 2
334+ value: s(115), refcnt: 6
335+ value: t(116), refcnt: 4
336+ value: u(117), refcnt: 1
337+ value: w(119), refcnt: 3
338+ ```
339+ 340+ 通过比较发现两者的结果大体是差不多的,但是第二个结果多了'?'。猜测多有一个'?'是因为t.py 中包含'?'。可是为什么在 Python shell 中,同样的`len('?')`却没有输出'?'呢?
341+ 342+ - 当 Python shell 启动之后,似乎 characters 被"冻结"了,无法再获取它的值。
343+ 344+ ``` python
345+ >> > len (' ?'
346+ value: / (47 ), refcnt: 12
347+ value: 1 (49 ), refcnt: 2
348+ value: E(69 ), refcnt: 1
349+ value: F(70 ), refcnt: 1
350+ value: N(78 ), refcnt: 1
351+ value: O(79 ), refcnt: 1
352+ value: R(82 ), refcnt: 1
353+ value: T(84 ), refcnt: 1
354+ value: W(87 ), refcnt: 1
355+ value: X(88 ), refcnt: 1
356+ value: _(95 ), refcnt: 7
357+ value: a(97 ), refcnt: 3
358+ value: c(99 ), refcnt: 4
359+ value: d(100 ), refcnt: 3
360+ value: e(101 ), refcnt: 2
361+ value: f(102 ), refcnt: 2
362+ value: g(103 ), refcnt: 1
363+ value: i(105 ), refcnt: 10
364+ value: k(107 ), refcnt: 8
365+ value: l(108 ), refcnt: 1
366+ value: m(109 ), refcnt: 6
367+ value: n(110 ), refcnt: 4
368+ value: o(111 ), refcnt: 1
369+ value: p(112 ), refcnt: 7
370+ value: r(114 ), refcnt: 2
371+ value: s(115 ), refcnt: 6
372+ value: t(116 ), refcnt: 4
373+ value: u(117 ), refcnt: 1
374+ value: w(119 ), refcnt: 3
375+ 1
376+ >> > a = ' x'
377+ >> > len (' ?'
378+ value: / (47 ), refcnt: 12
379+ value: 1 (49 ), refcnt: 2
380+ value: E(69 ), refcnt: 1
381+ value: F(70 ), refcnt: 1
382+ value: N(78 ), refcnt: 1
383+ value: O(79 ), refcnt: 1
384+ value: R(82 ), refcnt: 1
385+ value: T(84 ), refcnt: 1
386+ value: W(87 ), refcnt: 1
387+ value: X(88 ), refcnt: 1
388+ value: _(95 ), refcnt: 8
389+ value: a(97 ), refcnt: 4
390+ value: c(99 ), refcnt: 4
391+ value: d(100 ), refcnt: 3
392+ value: e(101 ), refcnt: 2
393+ value: f(102 ), refcnt: 2
394+ value: g(103 ), refcnt: 1
395+ value: i(105 ), refcnt: 10
396+ value: k(107 ), refcnt: 8
397+ value: l(108 ), refcnt: 1
398+ value: m(109 ), refcnt: 6
399+ value: n(110 ), refcnt: 4
400+ value: o(111 ), refcnt: 1
401+ value: p(112 ), refcnt: 7
402+ value: r(114 ), refcnt: 2
403+ value: s(115 ), refcnt: 6
404+ value: t(116 ), refcnt: 4
405+ value: u(117 ), refcnt: 1
406+ value: w(119 ), refcnt: 3
407+ 1
408+ ```
409+ 410+ 第一次执行` len('?') ` ,输出结果中没有'x',当定义` a = 'x' ` 之后,再次执行` len('?') ` ,输出结果中仍然没有'x'。从 stringobject.c 的代码来看,创建字符串时,假如长度为1,则会将其缓存到 characters 中。
411+ 412+ 会不会是只有在 Python 启动时才会缓存 characters。
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