为什么 PyScripter 控制台的输出不同？

Question

来自 PyScripter (3.6.4.0) REPL 控制台：

*** Python 3.7.7 (tags/v3.7.7:d7c567b08f, Mar 10 2020, 10:41:24) [MSC v.1900 64 bit (AMD64)] on win32. ***
*** Remote Python engine is active ***
>>> d = {}
>>> d['B'] = 12
>>> d['A'] = 10
>>> d['C'] = 34
>>> d
{'A': 10, 'B': 12, 'C': 34}

这个结果让我们相信 Python 对键进行排序并且不保留插入顺序，而从版本 3.6 开始就保证了。

现在让我们在 PyScripter 之外的控制台中运行完全相同的 Python 版本：

Python 3.7.7 (tags/v3.7.7:d7c567b08f, Mar 10 2020, 10:41:24) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> d = {}
>>> d['B'] = 12
>>> d['A'] = 10
>>> d['C'] = 34
>>> d
{'B': 12, 'A': 10, 'C': 34}

插入顺序全部保留。

为什么输出不同？

Answer 1

在 pyscripter REPL 中，当我不依赖 REPL 提供答案而是使用 print 语句时，我得到了正确的结果：

>>> print(d)
{'B': 12, 'A': 10, 'C': 34}

其中 d 生成的键就好像它们已排序一样：

>>> d
{'A': 10, 'B': 12, 'C': 34}

所以当涉及到字典顺序时，不要相信 pyscripter REPL 输出。

Answer 2

您需要在 pyscripter 中禁用 Pretty print output 选项：

If checked the standard python module pprint is used to format interpreter output.

在选项 > IDE 选项 > Python 解释器.

下找到它

pprint module 以排序的键顺序输出字典，忽略字典的当前顺序。来自文档：

Dictionaries are sorted by key before the display is computed.

匹配旧的 Python 版本输出不是 hack，因为在 Python 3.6 之前 order depended on insertion and deletion order plus a randomised hash seed.

相反，当输出变得笨拙时，使用 pprint 可以提供更好的输出，方法是使用换行符和缩进，其中标准表示只是将所有内容放在一行中。

你的具体例子并没有真正说明区别，更长的字典会更清楚：

>>> from requests import get
>>> from secrets import token_hex
>>> from pprint import pprint
>>> fortunes = {token_hex(4): get("https://fortuneapi.herokuapp.com/").text for _ in range(5)}
>>> print(repr(fortunes))  # standard REPL output prints the repr() result
{'a33435f0': '"If reporters don\'t know that truth is plural, they ought to be lawyers.\n\t\t-- Tom Wicker\n"\n', '1f08db3c': '"Very few profundities can be expressed in less than 80 characters.\n"\n', '6037e01e': '"The main problem I have with cats is, they\'re not dogs.\n\t\t-- Kevin Cowherd\n"\n', 'b817eaf8': '"New York now leads the world\'s great cities in the number of people around\nwhom you shouldn\'t make a sudden move.\n\t\t-- David Letterman\n"\n', 'c89994e7': '"I\'m GLAD I remembered to XEROX all my UNDERSHIRTS!!\n"\n'}
>>> pprint(fortunes)  # pprint outputs pretty-printed lines, sorted.
{'1f08db3c': '"Very few profundities can be expressed in less than 80 '
             'characters.\n"\n',
 '6037e01e': '"The main problem I have with cats is, they\'re not '
             'dogs.\n\t\t-- Kevin Cowherd\n"\n',
 'a33435f0': '"If reporters don\'t know that truth is plural, they ought to be '
             'lawyers.\n\t\t-- Tom Wicker\n"\n',
 'b817eaf8': '"New York now leads the world\'s great cities in the number of '
             "people around\nwhom you shouldn't make a sudden "
             'move.\n\t\t-- David Letterman\n"\n',
 'c89994e7': '"I\'m GLAD I remembered to XEROX all my UNDERSHIRTS!!\n"\n'}

如果您只是偶尔需要检查字典的特定项目顺序，您可以只启用该选项，并在那些特殊时间使用 print(dictionary)。

您也可以将 sort_dicts=False 参数传递给 pprint()，前提是您手动调用它； pprint.pp() function 甚至将其设为默认值：

>>> from pprint import pp
>>> pp(fortunes)
{'a33435f0': '"If reporters don\'t know that truth is plural, they ought to be '
             'lawyers.\n\t\t-- Tom Wicker\n"\n',
 '1f08db3c': '"Very few profundities can be expressed in less than 80 '
             'characters.\n"\n',
 '6037e01e': '"The main problem I have with cats is, they\'re not '
             'dogs.\n\t\t-- Kevin Cowherd\n"\n',
 'b817eaf8': '"New York now leads the world\'s great cities in the number of '
             "people around\nwhom you shouldn't make a sudden "
             'move.\n\t\t-- David Letterman\n"\n',
 'c89994e7': '"I\'m GLAD I remembered to XEROX all my UNDERSHIRTS!!\n"\n'
}

或者您可以要求 PyScripter 项目在其控制台实现中使用该选项。

为什么 PyScripter 控制台的输出不同？

Why is the output different in PyScripter console?

python

dictionary

pyscripter