# a=0100; print a ; 64 how to reverse this?

mensanator at aol.com mensanator at aol.com
Wed Jul 18 02:25:05 CEST 2007

```On Jul 17, 7:40 am, mosi <skawan... at gmail.com> wrote:
> Thank you,
> this is great,
> I thought that this should be standard in python 2.4 or 2.5 or in some
> standard library (math ???)
> Didn`t find anything.

You can also look up the gmpy module (not part of standard library).

It contains a lot of functions for use with binary numbers
(there are many others, I'm just showing the ones used for
binary numbers):

DESCRIPTION
gmpy 1.04 - General Multiprecision arithmetic for PYthon:
exposes functionality from the GMP 4 library to Python 2.{2,3,4}.

Allows creation of multiprecision integer (mpz), float (mpf),
and rational (mpq) numbers, conversion between them and to/from
Python numbers/strings, arithmetic, bitwise, and some other
higher-level mathematical operations; also, pretty good-quality
linear-congruential random number generation and shuffling.

mpz has comparable functionality to Python's builtin longs, but
can be faster for some operations (particularly multiplication
and raising-to-power) and has many further useful and speedy
functions (prime testing and generation, factorial, fibonacci,
binary-coefficients, gcd, lcm, square and other roots, ...).

mpf and mpq only offer basic arithmetic abilities, but they
do add the ability to have floating-point numbers ensuring at
least a predefined number of bits' worth of precision (and with
potentially-huge or extremely-tiny magnitudes), as well as
unlimited-precision rationals, with reasonably-fast operations,
which are not built-in features of Python.

FUNCTIONS

digits(...)
digits(x[,base]): returns Python string representing x in the
given base (2 to 36, default 10 if omitted or 0); leading '-'
present if x<0, but no leading '+' if x>=0. x must be an mpz,
or else gets coerced into one.

getbit(...)
getbit(x,n): returns 0 or 1, the bit-value of bit n of x;
n must be an ordinary Python int, >=0; x is an mpz, or else
gets coerced to one.

hamdist(...)
hamdist(x,y): returns the Hamming distance (number of bit-
positions
where the bits differ) between x and y.  x and y must be mpz,
or else
get coerced to mpz.

lowbits(...)
lowbits(x,n): returns the n lowest bits of x; n must be an
ordinary Python int, >0; x must be an mpz, or else gets
coerced to one.

numdigits(...)
numdigits(x[,base]): returns length of string representing x
in
the given base (2 to 36, default 10 if omitted or 0); the
value
returned may sometimes be 1 more than necessary; no provision
for any 'sign' characte, nor leading '0' or '0x' decoration,
is made in the returned length.  x must be an mpz, or else
gets
coerced into one.

popcount(...)
popcount(x): returns the number of 1-bits set in x; note that
this is 'infinite' if x<0, and in that case, -1 is returned.
x must be an mpz, or else gets coerced to one.

scan0(...)
scan0(x, n=0): returns the bit-index of the first 0-bit of x
(that
is at least n); n must be an ordinary Python int, >=0.  If no
more
0-bits are in x at or above bit-index n (which can only happen
for
x<0, notionally extended with infinite 1-bits), None is
returned.
x must be an mpz, or else gets coerced to one.

scan1(...)
scan1(x, n=0): returns the bit-index of the first 1-bit of x
(that
is at least n); n must be an ordinary Python int, >=0.  If no
more
1-bits are in x at or above bit-index n (which can only happen
for
x>=0, notionally extended with infinite 0-bits), None is
returned.
x must be an mpz, or else gets coerced to one.

setbit(...)
setbit(x,n,v=1): returns a copy of the value of x, with bit n
set
to value v; n must be an ordinary Python int, >=0; v, 0 or !
=0;
x must be an mpz, or else gets coerced to one.

```