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?
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.