Develop Reference

Zylabs 7.14 Lab: Reverse binary [duplicate]

Are there any canned Python methods to convert an Integer (or Long) into a binary string in Python?
There are a myriad of dec2bin() functions out on Google... But I was hoping I could use a built-in function / library.

Python's string format method can take a format spec.
>>> "{0:b}".format(37)
'100101'
Format spec docs for Python 2
Format spec docs for Python 3

If you're looking for bin() as an equivalent to hex(), it was added in python 2.6.
Example:
>>> bin(10)
'0b1010'

Python actually does have something already built in for this, the ability to do operations such as '{0:b}'.format(42), which will give you the bit pattern (in a string) for 42, or 101010.
For a more general philosophy, no language or library will give its user base everything that they desire. If you're working in an environment that doesn't provide exactly what you need, you should be collecting snippets of code as you develop to ensure you never have to write the same thing twice. Such as, for example, the pseudo-code:
define intToBinString, receiving intVal:
if intVal is equal to zero:
return "0"
set strVal to ""
while intVal is greater than zero:
if intVal is odd:
prefix "1" to strVal
else:
prefix "0" to strVal
divide intVal by two, rounding down
return strVal
which will construct your binary string based on the decimal value. Just keep in mind that's a generic bit of pseudo-code which may not be the most efficient way of doing it though, with the iterations you seem to be proposing, it won't make much difference. It's really just meant as a guideline on how it could be done.
The general idea is to use code from (in order of preference):
the language or built-in libraries.
third-party libraries with suitable licenses.
your own collection.
something new you need to write (and save in your own collection for later).

If you want a textual representation without the 0b-prefix, you could use this:
get_bin = lambda x: format(x, 'b')
print(get_bin(3))
>>> '11'
print(get_bin(-3))
>>> '-11'
When you want a n-bit representation:
get_bin = lambda x, n: format(x, 'b').zfill(n)
>>> get_bin(12, 32)
'00000000000000000000000000001100'
>>> get_bin(-12, 32)
'-00000000000000000000000000001100'
Alternatively, if you prefer having a function:
def get_bin(x, n=0):
"""
Get the binary representation of x.
Parameters
----------
x : int
n : int
Minimum number of digits. If x needs less digits in binary, the rest
is filled with zeros.
Returns
-------
str
"""
return format(x, 'b').zfill(n)

I am surprised there is no mention of a nice way to accomplish this using formatting strings that are supported in Python 3.6 and higher. TLDR:
>>> number = 1
>>> f'0b{number:08b}'
'0b00000001'
Longer story
This is functionality of formatting strings available from Python 3.6:
>>> x, y, z = 1, 2, 3
>>> f'{x} {y} {2*z}'
'1 2 6'
You can request binary as well:
>>> f'{z:b}'
'11'
Specify the width:
>>> f'{z:8b}'
' 11'
Request zero padding:
f'{z:08b}'
'00000011'
And add common prefix to signify binary number:
>>> f'0b{z:08b}'
'0b00000011'
You can also let Python add the prefix for you but I do not like it so much as the version above because you have to take the prefix into width consideration:
>>> f'{z:#010b}'
'0b00000011'
More info is available in official documentation on Formatted string literals and Format Specification Mini-Language.

As a reference:
def toBinary(n):
return ''.join(str(1 & int(n) >> i) for i in range(64)[::-1])
This function can convert a positive integer as large as 18446744073709551615, represented as string '1111111111111111111111111111111111111111111111111111111111111111'.
It can be modified to serve a much larger integer, though it may not be as handy as "{0:b}".format() or bin().

This is for python 3 and it keeps the leading zeros !
print(format(0, '08b'))

A simple way to do that is to use string format, see this page.
>> "{0:b}".format(10)
'1010'
And if you want to have a fixed length of the binary string, you can use this:
>> "{0:{fill}8b}".format(10, fill='0')
'00001010'
If two's complement is required, then the following line can be used:
'{0:{fill}{width}b}'.format((x + 2**n) % 2**n, fill='0', width=n)
where n is the width of the binary string.

one-liner with lambda:
>>> binary = lambda n: '' if n==0 else binary(n/2) + str(n%2)
test:
>>> binary(5)
'101'
EDIT:
but then :(
t1 = time()
for i in range(1000000):
binary(i)
t2 = time()
print(t2 - t1)
# 6.57236599922
in compare to
t1 = time()
for i in range(1000000):
'{0:b}'.format(i)
t2 = time()
print(t2 - t1)
# 0.68017411232

As the preceding answers mostly used format(),
here is an f-string implementation.
integer = 7
bit_count = 5
print(f'{integer:0{bit_count}b}')
Output:
00111
For convenience here is the python docs link for formatted string literals: https://docs.python.org/3/reference/lexical_analysis.html#f-strings.

Summary of alternatives:
n=42
assert "-101010" == format(-n, 'b')
assert "-101010" == "{0:b}".format(-n)
assert "-101010" == (lambda x: x >= 0 and str(bin(x))[2:] or "-" + str(bin(x))[3:])(-n)
assert "0b101010" == bin(n)
assert "101010" == bin(n)[2:] # But this won't work for negative numbers.
Contributors include John Fouhy, Tung Nguyen, mVChr, Martin Thoma. and Martijn Pieters.

>>> format(123, 'b')
'1111011'

For those of us who need to convert signed integers (range -2**(digits-1) to 2**(digits-1)-1) to 2's complement binary strings, this works:
def int2bin(integer, digits):
if integer >= 0:
return bin(integer)[2:].zfill(digits)
else:
return bin(2**digits + integer)[2:]
This produces:
>>> int2bin(10, 8)
'00001010'
>>> int2bin(-10, 8)
'11110110'
>>> int2bin(-128, 8)
'10000000'
>>> int2bin(127, 8)
'01111111'

you can do like that :
bin(10)[2:]
or :
f = str(bin(10))
c = []
c.append("".join(map(int, f[2:])))
print c

Using numpy pack/unpackbits, they are your best friends.
Examples
--------
>>> a = np.array([[2], [7], [23]], dtype=np.uint8)
>>> a
array([[ 2],
[ 7],
[23]], dtype=uint8)
>>> b = np.unpackbits(a, axis=1)
>>> b
array([[0, 0, 0, 0, 0, 0, 1, 0],
[0, 0, 0, 0, 0, 1, 1, 1],
[0, 0, 0, 1, 0, 1, 1, 1]], dtype=uint8)

Yet another solution with another algorithm, by using bitwise operators.
def int2bin(val):
res=''
while val>0:
res += str(val&1)
val=val>>1 # val=val/2
return res[::-1] # reverse the string
A faster version without reversing the string.
def int2bin(val):
res=''
while val>0:
res = chr((val&1) + 0x30) + res
val=val>>1
return res

numpy.binary_repr(num, width=None)
Examples from the documentation link above:
>>> np.binary_repr(3)
'11'
>>> np.binary_repr(-3)
'-11'
>>> np.binary_repr(3, width=4)
'0011'
The two’s complement is returned when the input number is negative and width is specified:
>>> np.binary_repr(-3, width=3)
'101'
>>> np.binary_repr(-3, width=5)
'11101'

The accepted answer didn't address negative numbers, which I'll cover.
In addition to the answers above, you can also just use the bin and hex functions. And in the opposite direction, use binary notation:
>>> bin(37)
'0b100101'
>>> 0b100101
37
But with negative numbers, things get a bit more complicated. The question doesn't specify how you want to handle negative numbers.
Python just adds a negative sign so the result for -37 would be this:
>>> bin(-37)
'-0b100101'
In computer/hardware binary data, negative signs don't exist. All we have is 1's and 0's. So if you're reading or producing binary streams of data to be processed by other software/hardware, you need to first know the notation being used.
One notation is sign-magnitude notation, where the first bit represents the negative sign, and the rest is the actual value. In that case, -37 would be 0b1100101 and 37 would be 0b0100101. This looks like what python produces, but just add a 0 or 1 in front for positive / negative numbers.
More common is Two's complement notation, which seems more complicated and the result is very different from python's string formatting. You can read the details in the link, but with an 8bit signed integer -37 would be 0b11011011 and 37 would be 0b00100101.
Python has no easy way to produce these binary representations. You can use numpy to turn Two's complement binary values into python integers:
>>> import numpy as np
>>> np.int8(0b11011011)
-37
>>> np.uint8(0b11011011)
219
>>> np.uint8(0b00100101)
37
>>> np.int8(0b00100101)
37
But I don't know an easy way to do the opposite with builtin functions. The bitstring package can help though.
>>> from bitstring import BitArray
>>> arr = BitArray(int=-37, length=8)
>>> arr.uint
219
>>> arr.int
-37
>>> arr.bin
'11011011'
>>> BitArray(bin='11011011').int
-37
>>> BitArray(bin='11011011').uint
219

Python 3.6 added a new string formatting approach called formatted string literals or “f-strings”.
Example:
name = 'Bob'
number = 42
f"Hello, {name}, your number is {number:>08b}"
Output will be 'Hello, Bob, your number is 00001010!'
A discussion of this question can be found here - Here

Unless I'm misunderstanding what you mean by binary string I think the module you are looking for is struct

n=input()
print(bin(n).replace("0b", ""))

def binary(decimal) :
otherBase = ""
while decimal != 0 :
otherBase = str(decimal % 2) + otherBase
decimal //= 2
return otherBase
print binary(10)
output:
1010

Here is the code I've just implemented. This is not a method but you can use it as a ready-to-use function!
def inttobinary(number):
if number == 0:
return str(0)
result =""
while (number != 0):
remainder = number%2
number = number/2
result += str(remainder)
return result[::-1] # to invert the string

Calculator with all neccessary functions for DEC,BIN,HEX:
(made and tested with Python 3.5)
You can change the input test numbers and get the converted ones.
# CONVERTER: DEC / BIN / HEX
def dec2bin(d):
# dec -> bin
b = bin(d)
return b
def dec2hex(d):
# dec -> hex
h = hex(d)
return h
def bin2dec(b):
# bin -> dec
bin_numb="{0:b}".format(b)
d = eval(bin_numb)
return d,bin_numb
def bin2hex(b):
# bin -> hex
h = hex(b)
return h
def hex2dec(h):
# hex -> dec
d = int(h)
return d
def hex2bin(h):
# hex -> bin
b = bin(h)
return b
## TESTING NUMBERS
numb_dec = 99
numb_bin = 0b0111
numb_hex = 0xFF
## CALCULATIONS
res_dec2bin = dec2bin(numb_dec)
res_dec2hex = dec2hex(numb_dec)
res_bin2dec,bin_numb = bin2dec(numb_bin)
res_bin2hex = bin2hex(numb_bin)
res_hex2dec = hex2dec(numb_hex)
res_hex2bin = hex2bin(numb_hex)
## PRINTING
print('------- DECIMAL to BIN / HEX -------\n')
print('decimal:',numb_dec,'\nbin: ',res_dec2bin,'\nhex: ',res_dec2hex,'\n')
print('------- BINARY to DEC / HEX -------\n')
print('binary: ',bin_numb,'\ndec: ',numb_bin,'\nhex: ',res_bin2hex,'\n')
print('----- HEXADECIMAL to BIN / HEX -----\n')
print('hexadec:',hex(numb_hex),'\nbin: ',res_hex2bin,'\ndec: ',res_hex2dec,'\n')

Somewhat similar solution
def to_bin(dec):
flag = True
bin_str = ''
while flag:
remainder = dec % 2
quotient = dec / 2
if quotient == 0:
flag = False
bin_str += str(remainder)
dec = quotient
bin_str = bin_str[::-1] # reverse the string
return bin_str

here is simple solution using the divmod() fucntion which returns the reminder and the result of a division without the fraction.
def dectobin(number):
bin = ''
while (number >= 1):
number, rem = divmod(number, 2)
bin = bin + str(rem)
return bin

Here's yet another way using regular math, no loops, only recursion. (Trivial case 0 returns nothing).
def toBin(num):
if num == 0:
return ""
return toBin(num//2) + str(num%2)
print ([(toBin(i)) for i in range(10)])
['', '1', '10', '11', '100', '101', '110', '111', '1000', '1001']

To calculate binary of numbers:
print("Binary is {0:>08b}".format(16))
To calculate the Hexa decimal of a number:
print("Hexa Decimal is {0:>0x}".format(15))
To Calculate all the binary no till 16::
for i in range(17):
print("{0:>2}: binary is {0:>08b}".format(i))
To calculate Hexa decimal no till 17
for i in range(17):
print("{0:>2}: Hexa Decimal is {0:>0x}".format(i))
##as 2 digit is enogh for hexa decimal representation of a number

try:
while True:
p = ""
a = input()
while a != 0:
l = a % 2
b = a - l
a = b / 2
p = str(l) + p
print(p)
except:
print ("write 1 number")

I found a method using matrix operation to convert decimal to binary.
import numpy as np
E_mat = np.tile(E,[1,M])
M_order = pow(2,(M-1-np.array(range(M)))).T
bindata = np.remainder(np.floor(E_mat /M_order).astype(np.int),2)
Eis input decimal data,M is the binary orders. bindata is output binary data, which is in a format of 1 by M binary matrix.

Decorating Hex function to pad zeros

I wrote this simple function:
def padded_hex(i, l):
given_int = i
given_len = l
hex_result = hex(given_int)[2:] # remove '0x' from beginning of str
num_hex_chars = len(hex_result)
extra_zeros = '0' * (given_len - num_hex_chars) # may not get used..
return ('0x' + hex_result if num_hex_chars == given_len else
'?' * given_len if num_hex_chars > given_len else
'0x' + extra_zeros + hex_result if num_hex_chars < given_len else
None)
Examples:
padded_hex(42,4) # result '0x002a'
hex(15) # result '0xf'
padded_hex(15,1) # result '0xf'
Whilst this is clear enough for me and fits my use case (a simple test tool for a simple printer) I can't help thinking there's a lot of room for improvement and this could be squashed down to something very concise.
What other approaches are there to this problem?

Use the new .format() string method:
>>> "{0:#0{1}x}".format(42,6)
'0x002a'
Explanation:
{ # Format identifier
0: # first parameter
# # use "0x" prefix
0 # fill with zeroes
{1} # to a length of n characters (including 0x), defined by the second parameter
x # hexadecimal number, using lowercase letters for a-f
} # End of format identifier
If you want the letter hex digits uppercase but the prefix with a lowercase 'x', you'll need a slight workaround:
>>> '0x{0:0{1}X}'.format(42,4)
'0x002A'
Starting with Python 3.6, you can also do this:
>>> value = 42
>>> padding = 6
>>> f"{value:#0{padding}x}"
'0x002a'

How about this:
print '0x%04x' % 42

If you don't need to handle negative numbers, you can do
"{:02x}".format(7) # '07'
"{:02x}".format(27) # '1b'
Where
: is the start of the formatting specification for the first argument {} to .format()
02 means "pad the input from the left with 0s to length 2"
x means "format as hex with lowercase letters"
You can also do this with f-strings:
f"{7:02x}" # '07'
f"{27:02x}" # '1b'

If just for leading zeros, you can try zfill function.
'0x' + hex(42)[2:].zfill(4) #'0x002a'

Use * to pass width and X for uppercase
print '0x%0*X' % (4,42) # '0x002A'
As suggested by georg and Ashwini Chaudhary

None of the answers are dealing well with negative numbers...
Try this:
val = 42
nbits = 16
'{:04X}'.format(val & ((1 << nbits)-1))

If you want to hold the preceding hex notation 0x you can also try this method too which is using the python3 f-strings.
f'0x{10:02x}' # 0x0a

Suppose you want to have leading zeros for hexadecimal number, for example you want 7 digit where your hexadecimal number should be written on, you can do like that :
hexnum = 0xfff
str_hex = hex(hexnum).rstrip("L").lstrip("0x") or "0"
'0'* (7 - len(str_hexnum)) + str_hexnum
This gives as a result :
'0000fff'

Convert base-2 binary number string to int

I'd simply like to convert a base-2 binary number string into an int, something like this:
>>> '11111111'.fromBinaryToInt()
255
Is there a way to do this in Python?

You use the built-in int() function, and pass it the base of the input number, i.e. 2 for a binary number:
>>> int('11111111', 2)
255
Here is documentation for Python 2, and for Python 3.

Just type 0b11111111 in python interactive interface:
>>> 0b11111111
255

Another way to do this is by using the bitstring module:
>>> from bitstring import BitArray
>>> b = BitArray(bin='11111111')
>>> b.uint
255
Note that the unsigned integer (uint) is different from the signed integer (int):
>>> b.int
-1
Your question is really asking for the unsigned integer representation; this is an important distinction.
The bitstring module isn't a requirement, but it has lots of performant methods for turning input into and from bits into other forms, as well as manipulating them.

Using int with base is the right way to go. I used to do this before I found int takes base also. It is basically a reduce applied on a list comprehension of the primitive way of converting binary to decimal ( e.g. 110 = 2**0 * 0 + 2 ** 1 * 1 + 2 ** 2 * 1)
add = lambda x,y : x + y
reduce(add, [int(x) * 2 ** y for x, y in zip(list(binstr), range(len(binstr) - 1, -1, -1))])

If you wanna know what is happening behind the scene, then here you go.
class Binary():
def __init__(self, binNumber):
self._binNumber = binNumber
self._binNumber = self._binNumber[::-1]
self._binNumber = list(self._binNumber)
self._x = [1]
self._count = 1
self._change = 2
self._amount = 0
print(self._ToNumber(self._binNumber))
def _ToNumber(self, number):
self._number = number
for i in range (1, len (self._number)):
self._total = self._count * self._change
self._count = self._total
self._x.append(self._count)
self._deep = zip(self._number, self._x)
for self._k, self._v in self._deep:
if self._k == '1':
self._amount += self._v
return self._amount
mo = Binary('101111110')

Here's another concise way to do it not mentioned in any of the above answers:
>>> eval('0b' + '11111111')
255
Admittedly, it's probably not very fast, and it's a very very bad idea if the string is coming from something you don't have control over that could be malicious (such as user input), but for completeness' sake, it does work.

A recursive Python implementation:
def int2bin(n):
return int2bin(n >> 1) + [n & 1] if n > 1 else [1]

If you are using python3.6 or later you can use f-string to do the
conversion:
Binary to decimal:
>>> print(f'{0b1011010:#0}')
90
>>> bin_2_decimal = int(f'{0b1011010:#0}')
>>> bin_2_decimal
90
binary to octal hexa and etc.
>>> f'{0b1011010:#o}'
'0o132' # octal
>>> f'{0b1011010:#x}'
'0x5a' # hexadecimal
>>> f'{0b1011010:#0}'
'90' # decimal
Pay attention to 2 piece of information separated by colon.
In this way, you can convert between {binary, octal, hexadecimal, decimal} to {binary, octal, hexadecimal, decimal} by changing right side of colon[:]
:#b -> converts to binary
:#o -> converts to octal
:#x -> converts to hexadecimal
:#0 -> converts to decimal as above example
Try changing left side of colon to have octal/hexadecimal/decimal.

For large matrix (10**5 rows and up) it is better to use a vectorized matmult. Pass in all rows and cols in one shot. It is extremely fast. There is no looping in python here. I originally designed it for converting many binary columns like 0/1 for like 10 different genre columns in MovieLens into a single integer for each example row.
def BitsToIntAFast(bits):
m,n = bits.shape
a = 2**np.arange(n)[::-1] # -1 reverses array of powers of 2 of same length as bits
return bits # a

For the record to go back and forth in basic python3:
a = 10
bin(a)
# '0b1010'
int(bin(a), 2)
# 10
eval(bin(a))
# 10

Convert bytes to bits in python

I am working with Python3.2. I need to take a hex stream as an input and parse it at bit-level. So I used
bytes.fromhex(input_str)
to convert the string to actual bytes. Now how do I convert these bytes to bits?

Another way to do this is by using the bitstring module:
>>> from bitstring import BitArray
>>> input_str = '0xff'
>>> c = BitArray(hex=input_str)
>>> c.bin
'0b11111111'
And if you need to strip the leading 0b:
>>> c.bin[2:]
'11111111'
The bitstring module isn't a requirement, as jcollado's answer shows, but it has lots of performant methods for turning input into bits and manipulating them. You might find this handy (or not), for example:
>>> c.uint
255
>>> c.invert()
>>> c.bin[2:]
'00000000'
etc.

What about something like this?
>>> bin(int('ff', base=16))
'0b11111111'
This will convert the hexadecimal string you have to an integer and that integer to a string in which each byte is set to 0/1 depending on the bit-value of the integer.
As pointed out by a comment, if you need to get rid of the 0b prefix, you can do it this way:
>>> bin(int('ff', base=16))[2:]
'11111111'
... or, if you are using Python 3.9 or newer:
>>> bin(int('ff', base=16)).removepreffix('0b')
'11111111'
Note: using lstrip("0b") here will lead to 0 integer being converted to an empty string. This is almost always not what you want to do.

Operations are much faster when you work at the integer level. In particular, converting to a string as suggested here is really slow.
If you want bit 7 and 8 only, use e.g.
val = (byte >> 6) & 3
(this is: shift the byte 6 bits to the right - dropping them. Then keep only the last two bits 3 is the number with the first two bits set...)
These can easily be translated into simple CPU operations that are super fast.

using python format string syntax
>>> mybyte = bytes.fromhex("0F") # create my byte using a hex string
>>> binary_string = "{:08b}".format(int(mybyte.hex(),16))
>>> print(binary_string)
00001111
The second line is where the magic happens. All byte objects have a .hex() function, which returns a hex string. Using this hex string, we convert it to an integer, telling the int() function that it's a base 16 string (because hex is base 16). Then we apply formatting to that integer so it displays as a binary string. The {:08b} is where the real magic happens. It is using the Format Specification Mini-Language format_spec. Specifically it's using the width and the type parts of the format_spec syntax. The 8 sets width to 8, which is how we get the nice 0000 padding, and the b sets the type to binary.
I prefer this method over the bin() method because using a format string gives a lot more flexibility.

I think simplest would be use numpy here. For example you can read a file as bytes and then expand it to bits easily like this:
Bytes = numpy.fromfile(filename, dtype = "uint8")
Bits = numpy.unpackbits(Bytes)

input_str = "ABC"
[bin(byte) for byte in bytes(input_str, "utf-8")]
Will give:
['0b1000001', '0b1000010', '0b1000011']

Here how to do it using format()
print "bin_signedDate : ", ''.join(format(x, '08b') for x in bytevector)
It is important the 08b . That means it will be a maximum of 8 leading zeros be appended to complete a byte. If you don't specify this then the format will just have a variable bit length for each converted byte.

To binary:
bin(byte)[2:].zfill(8)

Use ord when reading reading bytes:
byte_binary = bin(ord(f.read(1))) # Add [2:] to remove the "0b" prefix
Or
Using str.format():
'{:08b}'.format(ord(f.read(1)))

The other answers here provide the bits in big-endian order ('\x01' becomes '00000001')
In case you're interested in little-endian order of bits, which is useful in many cases, like common representations of bignums etc -
here's a snippet for that:
def bits_little_endian_from_bytes(s):
return ''.join(bin(ord(x))[2:].rjust(8,'0')[::-1] for x in s)
And for the other direction:
def bytes_from_bits_little_endian(s):
return ''.join(chr(int(s[i:i+8][::-1], 2)) for i in range(0, len(s), 8))

One line function to convert bytes (not string) to bit list. There is no endnians issue when source is from a byte reader/writer to another byte reader/writer, only if source and target are bit reader and bit writers.
def byte2bin(b):
return [int(X) for X in "".join(["{:0>8}".format(bin(X)[2:])for X in b])]

I came across this answer when looking for a way to convert an integer into a list of bit positions where the bitstring is equal to one. This becomes very similar to this question if you first convert your hex string to an integer like int('0x453', 16).
Now, given an integer - a representation already well-encoded in the hardware, I was very surprised to find out that the string variants of the above solutions using things like bin turn out to be faster than numpy based solutions for a single number, and I thought I'd quickly write up the results.
I wrote three variants of the function. First using numpy:
import math
import numpy as np
def bit_positions_numpy(val):
"""
Given an integer value, return the positions of the on bits.
"""
bit_length = val.bit_length() + 1
length = math.ceil(bit_length / 8.0) # bytelength
bytestr = val.to_bytes(length, byteorder='big', signed=True)
arr = np.frombuffer(bytestr, dtype=np.uint8, count=length)
bit_arr = np.unpackbits(arr, bitorder='big')
bit_positions = np.where(bit_arr[::-1])[0].tolist()
return bit_positions
Then using string logic:
def bit_positions_str(val):
is_negative = val < 0
if is_negative:
bit_length = val.bit_length() + 1
length = math.ceil(bit_length / 8.0) # bytelength
neg_position = (length * 8) - 1
# special logic for negatives to get twos compliment repr
max_val = 1 << neg_position
val_ = max_val + val
else:
val_ = val
binary_string = '{:b}'.format(val_)[::-1]
bit_positions = [pos for pos, char in enumerate(binary_string)
if char == '1']
if is_negative:
bit_positions.append(neg_position)
return bit_positions
And finally, I added a third method where I precomputed a lookuptable of the positions for a single byte and expanded that given larger itemsizes.
BYTE_TO_POSITIONS = []
pos_masks = [(s, (1 << s)) for s in range(0, 8)]
for i in range(0, 256):
positions = [pos for pos, mask in pos_masks if (mask & i)]
BYTE_TO_POSITIONS.append(positions)
def bit_positions_lut(val):
bit_length = val.bit_length() + 1
length = math.ceil(bit_length / 8.0) # bytelength
bytestr = val.to_bytes(length, byteorder='big', signed=True)
bit_positions = []
for offset, b in enumerate(bytestr[::-1]):
pos = BYTE_TO_POSITIONS[b]
if offset == 0:
bit_positions.extend(pos)
else:
pos_offset = (8 * offset)
bit_positions.extend([p + pos_offset for p in pos])
return bit_positions
The benchmark code is as follows:
def benchmark_bit_conversions():
# for val in [-0, -1, -3, -4, -9999]:
test_values = [
# -1, -2, -3, -4, -8, -32, -290, -9999,
# 0, 1, 2, 3, 4, 8, 32, 290, 9999,
4324, 1028, 1024, 3000, -100000,
999999999999,
-999999999999,
2 ** 32,
2 ** 64,
2 ** 128,
2 ** 128,
]
for val in test_values:
r1 = bit_positions_str(val)
r2 = bit_positions_numpy(val)
r3 = bit_positions_lut(val)
print(f'val={val}')
print(f'r1={r1}')
print(f'r2={r2}')
print(f'r3={r3}')
print('---')
assert r1 == r2
import xdev
xdev.profile_now(bit_positions_numpy)(val)
xdev.profile_now(bit_positions_str)(val)
xdev.profile_now(bit_positions_lut)(val)
import timerit
ti = timerit.Timerit(10000, bestof=10, verbose=2)
for timer in ti.reset('str'):
for val in test_values:
bit_positions_str(val)
for timer in ti.reset('numpy'):
for val in test_values:
bit_positions_numpy(val)
for timer in ti.reset('lut'):
for val in test_values:
bit_positions_lut(val)
for timer in ti.reset('raw_bin'):
for val in test_values:
bin(val)
for timer in ti.reset('raw_bytes'):
for val in test_values:
val.to_bytes(val.bit_length(), 'big', signed=True)
And it clearly shows the str and lookup table implementations are ahead of numpy. I tested this on CPython 3.10 and 3.11.
Timed str for: 10000 loops, best of 10
time per loop: best=20.488 µs, mean=21.438 ± 0.4 µs
Timed numpy for: 10000 loops, best of 10
time per loop: best=25.754 µs, mean=28.509 ± 5.2 µs
Timed lut for: 10000 loops, best of 10
time per loop: best=19.420 µs, mean=21.305 ± 3.8 µs

How can I make `bin(30)` return `00011110` instead of `0b11110`? [duplicate]

This question already has answers here:
Python int to binary string?
(36 answers)
Closed 3 years ago.
What does the b stand for in the output of bin(30): 0b11110? Is there any way I can get rid of this b? How can I get the output of bin() to always return a standard 8 digit output?

Using zfill():
Return the numeric string left filled with zeros in a string of length width. A sign prefix is handled correctly. The original string is returned if width is less than len(s).
>>> bin(30)[2:].zfill(8)
'00011110'
>>>

0b is like 0x - it indicates the number is formatted in binary (0x indicates the number is in hex).
See How do you express binary literals in python?
See http://docs.python.org/dev/whatsnew/2.6.html#pep-3127-integer-literal-support-and-syntax
To strip off the 0b it's easiest to use string slicing: bin(30)[2:]
And similarly for format to 8 characters wide:
('00000000'+bin(30)[2:])[-8:]
Alternatively you can use the string formatter (in 2.6+) to do it all in one step:
"{0:08b}".format(30)

Take advantage of the famous format() function with the lesser known second argument and chain it with zfill()
'b' - Binary
'x' - Hex
'o' - Octal
'd' - Decimal
>>> print format(30, 'b')
11110
>>> print format(30, 'b').zfill(8)
00011110
Should do. Here 'b' stands for binary just like 'x', 'o' & 'd' for hexadecimal, octal and decimal respectively.

You can use format in Python 2 or Python 3:
>> print( format(15, '08b') )
00001111
[]'s

You can use this too :
bi=bin(n)[2:]
This will remove the '0b' portion of the returned value and you can use the output anywhere .

The current answers don't consider negative values (thanks #Gui13 for the comment!) in which case you get -0b... instead of just 0b.... You can handle both with a simple if-else where the value is checked whether it's less than zero or not
>>> def printBit(x):
if x < 0:
return '-' + bin(x)[3:].zfill(8) # replace
else:
return bin(x)[2:].zfill(8)
>>> print(printBit(30))
'00011110'
>>> print(printBit(-30))
'-00011110'
or by using replace()
>>> print(bin(30)).replace('0b', '').zfill(8)
The problem with the call above is that one of the bits gets "lost" to the - sign due to the same value being used for the zfill(). You can handle this too with a simple ternary check:
>>> x = 30
>>> print(bin(x)).replace('0b', '').zfill(9 if x < 0 else 8)
'00011110'
>>> x = -30
>>> print(bin(x)).replace('0b', '').zfill(9 if x < 0 else 8)
'-00011110'
Last but not least you can also make the zfill() to automatically adapt the number of 0s to match a byte (8 bits) or a n number of bit quadruplets (4 bits):
>>> def pb(x):
bres = bin(x).replace('0b', '').replace('-', '') # If no minus, second replace doesn't do anything
lres = len(bres) # We need the length to see how many 0s we need to add to get a quadruplets
# We adapt the number of added 0s to get full bit quadruplets.
# The '-' doesn't count since we want to handle it separately from the bit string
bres = bres = ('-' if x < 0 else '') + bres.zfill(lres + (4-lres%4))
return bres
>>> print(pb(7))
'0111'
>>> print(pb(-7))
'-0111'
>>> print(pb(30))
'00011110'
>>> print(pb(-30))
'-00011110'
Here is the final version with adaptable filling of 0s and additional split with space every n characters (where the n is determined by filling factor):
>>> def pb(x, fillingBits=4, splitWithSpace=True):
# If no minus, second replace doesn't do anything
bres = bin(x).replace('0b', '').replace('-', '')
lres = len(bres)
bres = bres.zfill(lres + (fillingBits - (lres % fillingBits)))
lres = len(bres)
# We can also add a blank after every fillingBits character
if splitWithSpace:
bres = ' '.join([bres[i:(i + fillingBits)] for i in range(0, lres, fillingBits)])
bres = ('-' if x < 0 else '') + bres
# We remove any trailing/leading blanks (occurring whenever splitWithSpace enabled)
return bres.strip()
>>> print(pb(7))
'0111'
>>> print(pb(-7))
'-0111'
>>> print(pb(30))
'0001 1110'
>>> print(pb(-30))
'-0001 1110'

python 2.7
print "{0:b}".format(30)
python 3.x
print ('{0:b}'.format(30))