我该如何解决这种 python 表达式？

Question

I have two expressions like given below:

a,b,c=2,4,5

print(a|b*c)
output : 22

How it is returning me the 22

and second expression is:

print(a|b^c)

output : 3

Can anyone please explain to me how python calculating this? I am a newbie in python I don't know how it is calculating this.

Answer 1

EXPRESSION # 1

Lets consider,

a|b*c

Precedence of * (multiplication) is greater than | (bitwise OR) thats why first b*c will be computed and then its output will be computed with a

STEPS:

1- b*c will return 20.

2- Then a will perform bit wise OR operation with b*c . SeeBitwise OR operation ( OR returns 1 when there is any one else 0)

3- Convert values of a and b*c to binary and perform bitwise operation. SeeConvert decimal to binary

      1 0     > a = 2
1 0 1 0 0     > b*c = 20
_________
1 0 1 1 0     > a|b*c = 22

EXPRESSION # 2

Lets consider,

a|b^c

Precedence of ^ (bitwise XOR) is greater than | (bitwise OR) thats why first b^c will be computed and then its output will be computed with a

STEPS:

1- Bitwise XOR operation will be performed between b and c (b^c). SeeBitwise XOR operation ( XOR returns 1 when there are odd number of ones else 0)

1 0 0   > b = 4
1 0 1   > c = 5
______   
0 0 1   > b^c = 1

2- Then a will perform bit wise OR operation with b^c . SeeBitwise OR operation ( OR returns 1 when there is any one else 0)

1 0   > a =2
0 1   > b^c = 1
___
1 1   > a|b^c = 3

Answer 2

print(a|b*c)

Because of the operator precedence , the multiplication ( * ) will be processed before the bitwise OR ( | ), so the operations will happen in the following order:

1. b*c = 4*5 = 20
2. a|b*c = 2|20 , ie 10 OR 10100 = 10110 in binary

That gives us a final answer of 22 .

print(a|b^c)

Likewise, due to the operator precedence , the bitwise XOR ( ˆ ) will be processed first, so we'll have:

1. bˆc = 4ˆ5 , ie 100 XOR 101 = 001 in binary
2. a|bˆc = 2|1 , ie 10 OR 01 = 11 in binary

That gives us a final answer of 3 .

Answer 3

This is doing a mix of bitwise and integer arithmetic operations.

How does that work?

Based on the order of precedence of operators defined in the docs , the first expression to be evaluated is b*c, which returns 20. Then we evaluate the expression a|20. This is a bitwise operation on the two integers, so what we are doing is doing a logical OR on each bit of the binary representation of these two numbers ie (00010) | (10100) which gives us (10110) ie 22

Similarly, in the second example, we first do XOR on b and c, which is equal to 1 (calculated as binary 100 XOR 101 = 001). The result is then bitwise ORed with a, returning the value 3

Answer 4

The Precedence of arithmetic operators * , /, +, - is more than bitwise operators &, |, ^ and both types of operators are evaluated left to right if the same precedence is found.

Moreover,

• for arithmetic operator precedence order is: * ,/ then +,-
• and for bitwise operator precedence order is: &, ^, |

Check this article for more information

Coming to the solution:

1. The first expression evaluates like this: a|(b*c)
2. The second expression evaluates like this: a|(b^c)

Answer 5

You need to break down the numbers into their binary representation to see what's happening under the hood.

Case 1,

Binary for a (2) - 00010

Binary for b*c (20) - 10100

So if you do a bitwise OR (|) you'll get a binary sum of above two ie 10110 = 22

Case 2,

Binary for a (2) - 00010

Binary for b (4) - 00100

Binary for c (5) - 00101

Again if you do a bitwise XOR (^) you'll get a binary exclusive or of b and c ie 00001= 1

Finally if you do a bitwise OR (|) you'll get a binary sum of a with b^c ie 00011 = 3