Implementing-cryptography-using-python

Chapter 1 ■ Introduction to Cryptography and Python 15
Understanding Bitwise Operators
The bitwise operators work on bits and perform bit-by-bit operations (see Table 1.6).
Assuming a = 60 and b = 13, the binary format of a and b will be as follows:
a = 0011 1100
b = 0000 1101
Table 1.6: Bitwise Operators
OPERATOR DESCRIPTION EXAMPLE
& (binary AND)
Copies a bit to the result if it exists in
both operands.
| (binary OR) Copies a bit if it exists in either
operand.
^ (binary XOR)
~ (binary One
Complement)
<< (binary Left
Shift)
>> (binary Right
Shift)
Copies the bit if it is set in one operand
but not both.
This operator is unary and has the
effect of “flipping” bits.
The left operand’s value is moved left
by the number of bits specified by the
right operand.
The left operand’s value is moved
right by the number of bits specified
by the right operand.
(a & b) (means 0000
1100)
(a | b) = 61 (means
0011 1101)
(a ^ b) = 49 (means
0011 0001)
(~a ) =-61 (means 1100
0011 in two’s
complement form due to
a signed binary number.
a << 2 = 240 (means
1111 0000)
a >> 2 = 15 (means
0000 1111)
Understanding Membership Operators
Membership operators test for membership in a sequence, such as strings, lists,
or tuples. There are two membership operators, in and not in, as shown in
Table 1.7.
Table 1.7: Membership Operators
OPERATOR DESCRIPTION EXAMPLE
in
not in
Evaluates to true if it finds a variable in
the specified sequence and false
otherwise.
Evaluates to true if it does not find a
variable in the specified sequence and
false otherwise.
x in y; here in results in a
1 if x is a member of
sequence y.
x not in y; here not in
results in a 1 if x is not a
member of sequence y.