在 Python 赋值运算符中使用逗号和下划线的含义? [英] Meaning of using commas and underscores with Python assignment operator?

问题描述

通读 Peter Norvig 的 解决每篇数独谜题，我遇到了一些 Python 习语以前从未见过.

我知道函数可以返回一个元组/值列表，在这种情况下，您可以为结果分配多个变量，例如

def f():返回 1,2a, b = f()

但以下每一项的含义是什么?

d2, = values[s] ## values[s] 是一个字符串，此时 len(values[s]) 是 1

如果len(values[s]) == 1，那么这个语句与d2 = values[s]有什么不同?

关于在此处的作业中使用下划线的另一个问题:

_,s = min((len(values[s]), s) for s in squares if len(values[s]) > 1)

下划线是否有基本丢弃列表中返回的第一个值的作用?

解决方案

d2, = values[s] 和 a,b=f() 一样，除了用于解包 1 个元素的元组.

<预><代码>>>>T=(1,)>>>a=T>>>一种(1,)>>>b,=T>>>乙1>>>

a 是元组，b 是整数.

Reading through Peter Norvig's Solving Every Sudoku Puzzle essay, I've encountered a few Python idioms that I've never seen before.

I'm aware that a function can return a tuple/list of values, in which case you can assign multiple variables to the results, such as

def f():
    return 1,2

a, b = f()

But what is the meaning of each of the following?

d2, = values[s]  ## values[s] is a string and at this point len(values[s]) is 1

If len(values[s]) == 1, then how is this statement different than d2 = values[s]?

Another question about using an underscore in the assignment here:

_,s = min((len(values[s]), s) for s in squares if len(values[s]) > 1)

Does the underscore have the effect of basically discarding the first value returned in the list?

解决方案

d2, = values[s] is just like a,b=f(), except for unpacking 1 element tuples.

>>> T=(1,)
>>> a=T
>>> a
(1,)
>>> b,=T
>>> b
1
>>> 

a is tuple, b is an integer.

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