“(1,) == 1,"是什么意思?在 Python 中?

2022-01-20 00:00:00 python tuples equals-operator

问题描述

我正在测试元组结构，发现使用 == 运算符时很奇怪:

I'm testing the tuple structure, and I found it's strange when I use the == operator like:

>>>  (1,) == 1,
Out: (False,)

当我将这两个表达式赋值给一个变量时，结果为真:

When I assign these two expressions to a variable, the result is true:

>>> a = (1,)
>>> b = 1,
>>> a==b
Out: True

这个问题不同于我的 Python tuple trailing comma syntax rule看法.我问 == 运算符之间的表达式组.

This questions is different from Python tuple trailing comma syntax rule in my view. I ask the group of expressions between == operator.

解决方案

其他答案已经向您表明该行为是由于运算符优先级引起的，如文档 这里.

Other answers have already shown you that the behaviour is due to operator precedence, as documented here.

下次您遇到类似的问题时，我将向您展示如何自己找到答案.您可以使用 ast 解构表达式的解析方式模块:

I'm going to show you how to find the answer yourself next time you have a question similar to this. You can deconstruct how the expression parses using the ast module:

>>> import ast
>>> source_code = '(1,) == 1,'
>>> print(ast.dump(ast.parse(source_code), annotate_fields=False))
Module([Expr(Tuple([Compare(Tuple([Num(1)], Load()), [Eq()], [Num(1)])], Load()))])

从这里我们可以看到代码被解析正如蒂姆·彼得斯解释的那样:

From this we can see that the code gets parsed as Tim Peters explained: 

Module([Expr(
    Tuple([
        Compare(
            Tuple([Num(1)], Load()), 
            [Eq()], 
            [Num(1)]
        )
    ], Load())
)])

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