python按位运算的奇怪结果

Question

Anyone could explain? I get really confused by the following outcome. Thanks a lot!

why this doesn't work!???

`i = 2
table[i] = i&1 + table[i>>1] `

the following works

`tmp = i&1
 table[i] = tmp + table[i>>1]`

Answer 1

This is because of parens gruopings and & having less precedence: Here's an example of how this works:

2& will not happen until 2+ 2 >> 2
In [569]: 2&2 + 2>>2                                                                                                                                                                           
Out[569]: 0

Here we use the and in parens first, before adding to 2>>2
In [570]: (2&2) + 2>>2                                                                                                                                                                         
Out[570]: 1

Here's what the operator precedence looks like for the original operation:
In [571]: 2&(2 + 2>>2)                                                                                                                                                                         
Out[571]: 0