Erro: python boolean

Question

def INSERTION_SORT(A):
    for j in range(len(A)-1):
        key = A[j]
        i = j+1
        print("***********")
        print(j >= 0)
        print(key > A[i])
        print(j >= 0 & key > A[i])

A = [5,2,4,6,1,3]

INSERTION_SORT(A)

operation result：

***********
True
True
False
***********
True
False
False
***********
True
False
False
***********
True
True
False
***********
True
False
False
[Finished in 52ms]

why are all true, the result is false

Only for `j >= 0` are "all true", and that's because for `for j in range(len(A)-1)`, all `j >= 0`. What exactly is your question? — tobias_k, Jan 10 '22 at 13:34
What is meant by "why are all true, the result is false"? There isn't a result anywhere in this code. It's not clear to me what it's supposed to do, seeing how ``INSERTION_SORT`` doesn't insert anything. — MisterMiyagi, Jan 10 '22 at 13:35
In particular, note that `j >= 0 & key > A[i]` is _not_ `(j >= 0) & (key > A[i])` but `j >= (0 & key) > A[i]`, i.e. `j >= 0 > A[i]`. First comparison is true, second comparison is false for all values, hence the entire chained comparison is false. — tobias_k, Jan 10 '22 at 13:36
Use the keyword `and`, not `&` because `&` is a bit operator. In Python `and` and `or` are used for boolean comparisons. It should be like this `print(j >= 0 and key > A[i])` — timmyx, Jan 10 '22 at 13:46
Please don't invalidate existing answers via edits. The new question state makes the answers fail to even address the question. — MisterMiyagi, Jan 10 '22 at 14:09

score 0 · Answer 1 · answered Jan 10 '22 at 13:34

0

You should use and keyword instead of &

and: this is the logical and
&: this is the bitwise operator

answered Jan 10 '22 at 13:34

Paul Kocian

487
4
20

1

Note that ``True & True`` is ``True``. The problem isn't that one works "logically" and the other "bitwise". – MisterMiyagi Jan 10 '22 at 13:36
1

The real problem is the different operator precedence. `and` is evaluated after comparisons, whereas `&` is evaluated before. – tobias_k Jan 10 '22 at 13:39
So if first condition is false, the other one will not be checked if Im using `&`? – Paul Kocian Jan 10 '22 at 13:40
1

No, that's lazy evaluation. See my comment on the question. With `&`, there are not "two conditions", but just a single chained comparison. – tobias_k Jan 10 '22 at 13:41
Ah ok. Understood thanks – Paul Kocian Jan 10 '22 at 13:42

score 0 · Answer 2 · answered Jan 10 '22 at 13:35

0

You are using the bitwise operator &, in the line print(j >= 0 & key > A[i]). Instead you can use and logical and operator. By the way, your code is not yet doing any sorting operation.

answered Jan 10 '22 at 13:35

Anand Sowmithiran

2,591
2
10
22

Erro: python boolean

2 Answers2