为什么在Python解释器中键入_会返回True? [英] Why does typing _ in the Python interpreter return True?

问题描述

我的口译员行为很奇怪:

I am getting very weird interpreter behaviour:

>>> _
True
>>> type(True)
<class 'bool'>
>>> type(_)
<class 'bool'>

我之所以这样做是因为_是Bpython中的一个建议，但它似乎也可以在普通解释器中使用.我正在使用

I tried this because _ came up as a suggestion in Bpython, but it seems to work in the normal interpreter too. I am using

Python 3.3.3 (v3.3.3:c3896275c0f6, Nov 16 2013, 23:39:35) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin

有人可以解释_为什么用_代替True吗?是否是旧式的，类似于;"可以用来结束命令，但这不是必需/不鼓励的吗?

Can anybody explain why _ is a substitute for True? Is it legacy, similarly to how ";" can be used to end commands, but is not necessary/encouraged?

这似乎是随机的.在新的终端中不会发生这种情况，但是一旦我开始从事某件事，_就开始成为现实.到底是怎么回事?

It seems to be random. This does not happen in a new terminal, but once I start working on something _ starts becoming true. What the hell is going on?

推荐答案

_将是最后计算的命令的结果-解释器启动时没有任何内容，因此您会得到NameError. .之后，您将得到以前的结果...尝试打开一个新的解释器并执行2 + 2 ...，您将看到返回的4，然后键入_ ...，例如:

_ will be the result of the last evaluated command - at interpreter start up there isn't any so you'll get a NameError... after that, you'll get the previous result... Try opening a new interpreter and doing 2 + 2... you'll see 4 returned, then type _... eg:

>>> _

Traceback (most recent call last):
  File "<pyshell#18>", line 1, in <module>
    _
NameError: name '_' is not defined
>>> 2 + 2
4
>>> _
4

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