Bit Manipulation Operators
We've already seen the usual math operators: +, -, *, /, %, **; as
well as the
functions. There are several other operators available to us. Principally,
these are for manipulating the individual bits of an integer value.
The unary ~ operator flops all the bits in a plain or long integer.
1's become 0's and 0's become 1's. Since most hardware uses a technique
called 2's complement, this is mathematically equivalent to adding 1 and
switching the number's sign.
There are binary bit manipulation operators, also. These perform
simple Boolean operations on all bits of the integer at once.
The binary & operator returns a 1-bit if the two input bits are
print 0&0, 1&0, 1&1, 0&1
0 0 1 0
Here's the same kind of example, combining sequences of bits. This
takes a bit of conversion to base 2 to understand what's going on.
The number 3, in base 2, is
0011. The number 5 is
0101. Let's match up the bits from left to
0 0 1 1
& 0 1 0 1
0 0 0 1
The binary ^ operator returns a 1-bit if one of the two inputs are 1
but not both. This is sometimes called the exclusive or.
Let's look at the individual bits
0 0 1 1
^ 0 1 0 1
0 1 1 0
Which is the binary representation of the number 6.
The binary | operator returns a 1-bit if either of the two inputs is
1. This is sometimes called the inclusive or. Sometimes this is written
Let's look at the individual bits.
0 0 1 1
| 0 1 0 1
0 1 1 1
Which is the binary representation of the number 7.
There are also bit shifting operations. These are mathematically
equivalent to multiplying and dividing by powers of two. Often, machine
hardware can execute these operations faster than the equivalent multiply
The << is the left-shift operator. The left argument is the
bit pattern to be shifted, the right argument is the number of
print 0xA << 2
0xA is hexadecimal; the bits are 1-0-1-0. This is
10 in decimal. When we shift this two bits to the left, it's like
multiplying by 4. We get bits of 1-0-1-0-0-0. This is 40 in
The >> is the right-shift operator. The left argument is the
bit pattern to be shifted, the right argument is the number of bits.
Python always behaves as though it is running on a 2's complement
computer. The left-most bit is always the sign bit, so sign bits are
print 80 >> 3
The number 80, with bits of 1-0-1-0-0-0-0, shifted right 3 bits,
yields bits of 1-0-1-0, which is 10 in decimal.
There are some other operators available, but, strictly speaking,
they're not arithmetic operators, they're logic operations. We'll return
to them in Chapter 7, Truth, Comparison and Conditional