How to convert a string of bytes into an int

Question

How can I convert a string of bytes into an int in python    Say like this   y xcc xa6 xbb   I came up with a clever stupid way of doing it   sum ord c   lt  lt   i   8  for i  c in enumerate  y xcc xa6 xbb    -1      I know there has to be something builtin or in the standard library that does this more simply     This is different from converting a string of hex digits for which you can use int xxx  16   but instead I want to convert a string of actual byte values   UPDATE   I kind of like James  answer a little better because it doesn t require importing another module  but Greg s method is faster    gt  gt  gt  from timeit import Timer  gt  gt  gt  Timer  struct unpack   lt L    y xcc xa6 xbb   0     import struct   timeit   0 36242198944091797  gt  gt  gt  Timer  int  y xcc xa6 xbb  encode  hex    16    timeit   1 1432669162750244   My hacky method    gt  gt  gt  Timer  sum ord c   lt  lt   i   8  for i  c in enumerate  y xcc xa6 xbb    -1      timeit   2 8819329738616943   FURTHER UPDATE   Someone asked in comments what s the problem with importing another module  Well  importing a module isn t necessarily cheap  take a look    gt  gt  gt  Timer    import struct nstruct unpack   gt L    y xcc xa6 xbb   0      timeit   0 98822188377380371   Including the cost of importing the module negates almost all of the advantage that this method has  I believe that this will only include the expense of importing it once for the entire benchmark run  look what happens when I force it to reload every time    gt  gt  gt  Timer    reload struct  nstruct unpack   gt L    y xcc xa6 xbb   0       import struct   timeit   68 474128007888794   Needless to say  if you re doing a lot of executions of this method per one import than this becomes proportionally less of an issue  It s also probably i o cost rather than cpu so it may depend on the capacity and load characteristics of the particular machine

User · Answer

I use the following function to convert data between int, hex and bytes.

def bytes2int(str):
 return int(str.encode('hex'), 16)

def bytes2hex(str):
 return '0x'+str.encode('hex')

def int2bytes(i):
 h = int2hex(i)
 return hex2bytes(h)

def int2hex(i):
 return hex(i)

def hex2int(h):
 if len(h) > 1 and h[0:2] == '0x':
  h = h[2:]

 if len(h) % 2:
  h = "0" + h

 return int(h, 16)

def hex2bytes(h):
 if len(h) > 1 and h[0:2] == '0x':
  h = h[2:]

 if len(h) % 2:
  h = "0" + h

 return h.decode('hex')

Source: http://opentechnotes.blogspot.com.au/2014/04/convert-values-to-from-integer-hex.html

User · Answer

In Python 3 2 and later  use   gt  gt  gt  int from bytes b y xcc xa6 xbb   byteorder  big   2043455163   or   gt  gt  gt  int from bytes b y xcc xa6 xbb   byteorder  little   3148270713   according to the endianness of your byte-string   This also works for bytestring-integers of arbitrary length  and for two s-complement signed integers by specifying signed True  See the docs for from bytes

User · Answer

As mentioned above using unpack function of struct is a good way  If you want to implement your own function there is an another solution   def bytes to int bytes       result   0     for b in bytes          result   result   256   int b  return result

User · Answer

As Greg said  you can use struct if you are dealing with binary values  but if you just have a  hex number  but in byte format you might want to just convert it like   s    y xcc xa6 xbb  num   int s encode  hex    16       this is the same as   num   struct unpack   L   s  0       except it ll work for any number of bytes

User · Answer

int from bytes is the best solution if you are at version   3 2  The  struct unpack  solution requires a string so it will not apply to arrays of bytes  Here is another solution   def bytes2int  tb  order  big        if order     big   seq  0 1 2 3      elif order     little   seq  3 2 1 0      i   0     for j in seq  i    i lt  lt 8  tb j      return i   hex  bytes2int   0x87  0x65  0x43  0x21    returns  0x87654321    It handles big and little endianness and is easily modifiable for 8 bytes

User · Answer

As Greg said  you can use struct if you are dealing with binary values  but if you just have a  hex number  but in byte format you might want to just convert it like   s    y xcc xa6 xbb  num   int s encode  hex    16       this is the same as   num   struct unpack   L   s  0       except it ll work for any number of bytes

User · Answer

As Greg said  you can use struct if you are dealing with binary values  but if you just have a  hex number  but in byte format you might want to just convert it like   s    y xcc xa6 xbb  num   int s encode  hex    16       this is the same as   num   struct unpack   L   s  0       except it ll work for any number of bytes

User · Answer

In Python 2 x  you could use the format specifiers  lt B for unsigned bytes  and  lt b for signed bytes with struct unpack struct pack   E g   Let x     xff x10 x11   data ints   struct unpack   lt      B  len x   x     255  16  17    And   data bytes   struct pack   lt      B  len data ints    data ints      xff x10 x11    That   is required   See https   docs python org 2 library struct html format-characters for a list of the format specifiers

User · Answer

import array integerValue   array array  I    y xcc xa6 xbb   0    Warning  the above is strongly platform-specific  Both the  I  specifier and the endianness of the string- int conversion are dependent on your particular Python implementation  But if you want to convert many integers strings at once  then the array module does it quickly

User · Answer

As Greg said  you can use struct if you are dealing with binary values  but if you just have a  hex number  but in byte format you might want to just convert it like   s    y xcc xa6 xbb  num   int s encode  hex    16       this is the same as   num   struct unpack   L   s  0       except it ll work for any number of bytes

User · Answer

You can also use the struct module to do this    gt  gt  gt  struct unpack   lt L    y xcc xa6 xbb   0  3148270713L

User · Answer

import array integerValue   array array  I    y xcc xa6 xbb   0    Warning  the above is strongly platform-specific  Both the  I  specifier and the endianness of the string- int conversion are dependent on your particular Python implementation  But if you want to convert many integers strings at once  then the array module does it quickly

User · Answer

I was struggling to find a solution for arbitrary length byte sequences that would work under Python 2 x  Finally I wrote this one  it s a bit hacky because it performs a string conversion  but it works   Function for Python 2 x  arbitrary length  def signedbytes data          Convert a bytearray into an integer  considering the first bit as     sign  The data must be big-endian         negative   data 0   amp  0x80  gt  0      if negative          inverted   bytearray  d   256 for d in data          return -signedbytes inverted  - 1      encoded   str data  encode  hex       return int encoded  16    This function has two requirements    The input data needs to be a bytearray  You may call the function like this   s    y xcc xa6 xbb  n   signedbytes s   The data needs to be big-endian  In case you have a little-endian value  you should reverse it first   n   signedbytes s   -1      Of course  this should be used only if arbitrary length is needed  Otherwise  stick with more standard ways  e g  struct

User · Answer

I use the following function to convert data between int, hex and bytes.

def bytes2int(str):
 return int(str.encode('hex'), 16)

def bytes2hex(str):
 return '0x'+str.encode('hex')

def int2bytes(i):
 h = int2hex(i)
 return hex2bytes(h)

def int2hex(i):
 return hex(i)

def hex2int(h):
 if len(h) > 1 and h[0:2] == '0x':
  h = h[2:]

 if len(h) % 2:
  h = "0" + h

 return int(h, 16)

def hex2bytes(h):
 if len(h) > 1 and h[0:2] == '0x':
  h = h[2:]

 if len(h) % 2:
  h = "0" + h

 return h.decode('hex')

Source: http://opentechnotes.blogspot.com.au/2014/04/convert-values-to-from-integer-hex.html

User · Answer

import array integerValue   array array  I    y xcc xa6 xbb   0    Warning  the above is strongly platform-specific  Both the  I  specifier and the endianness of the string- int conversion are dependent on your particular Python implementation  But if you want to convert many integers strings at once  then the array module does it quickly

User · Answer

gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  y xcc xa6 xbb    2043455163   Test 1  inverse    gt  gt  gt  hex 2043455163   0x79cca6bb    Test 2  Number of bytes   8    gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAAA    338822822454978555838225329091068225L   Test 3  Increment by one    gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAAB    338822822454978555838225329091068226L   Test 4  Append one byte  say  A     gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAABA    86738642548474510294585684247313465921L   Test 5  Divide by 256    gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAABA    256 338822822454978555838225329091068226L   Result equals the result of Test 4  as expected

User · Answer

A decently speedy method utilizing array array I ve been using for some time   predefined variables   offset   0 size   4 big   True   endian arr   array  B   arr fromstring   x00 x00 xff x00     5 bytes  encoding issues   0  0  195  191  0    to int   read   val   0 for v in arr offset offset size    pow -1 not big    val    val lt  lt 8  v   from int   write   val   16384 arr offset offset size          array  B    val gt  gt  i lt  lt 3   amp 255 for i in range size      pow -1 not big     It s possible these could be faster though   EDIT  For some numbers  here s a performance test  Anaconda 2 3 0  showing stable averages on read in comparison to reduce                               byte array to int py                           5000 iterations  threshold of min   5000ns                                        code           min              max              avg        efficiency                                                                                                                                       val   0  nfor v in arr  val    val lt  lt 8  v       5373 848ns     850009 965ns        8649 64ns    62 128                                                                                                                                                      val   reduce  shift  arr         6489 921ns    5094212 014ns      12040 269ns    53 902    This is a raw performance test  so the endian pow-flip is left out  The shift function shown applies the same shift-oring operation as the for loop  and arr is just array array  B   0 0 255 0   as it has the fastest iterative performance next to dict   I should probably also note efficiency is measured by accuracy to the average time

User · Answer

In python 3 you can easily convert a byte string into a list of integers  0  255  by   gt  gt  gt  list b y xcc xa6 xbb    121  204  166  187

User · Answer

I was struggling to find a solution for arbitrary length byte sequences that would work under Python 2 x  Finally I wrote this one  it s a bit hacky because it performs a string conversion  but it works   Function for Python 2 x  arbitrary length  def signedbytes data          Convert a bytearray into an integer  considering the first bit as     sign  The data must be big-endian         negative   data 0   amp  0x80  gt  0      if negative          inverted   bytearray  d   256 for d in data          return -signedbytes inverted  - 1      encoded   str data  encode  hex       return int encoded  16    This function has two requirements    The input data needs to be a bytearray  You may call the function like this   s    y xcc xa6 xbb  n   signedbytes s   The data needs to be big-endian  In case you have a little-endian value  you should reverse it first   n   signedbytes s   -1      Of course  this should be used only if arbitrary length is needed  Otherwise  stick with more standard ways  e g  struct

User · Answer

In Python 2 x  you could use the format specifiers  lt B for unsigned bytes  and  lt b for signed bytes with struct unpack struct pack   E g   Let x     xff x10 x11   data ints   struct unpack   lt      B  len x   x     255  16  17    And   data bytes   struct pack   lt      B  len data ints    data ints      xff x10 x11    That   is required   See https   docs python org 2 library struct html format-characters for a list of the format specifiers

User · Answer

In python 3 you can easily convert a byte string into a list of integers  0  255  by   gt  gt  gt  list b y xcc xa6 xbb    121  204  166  187

User · Answer

In Python 3 2 and later  use   gt  gt  gt  int from bytes b y xcc xa6 xbb   byteorder  big   2043455163   or   gt  gt  gt  int from bytes b y xcc xa6 xbb   byteorder  little   3148270713   according to the endianness of your byte-string   This also works for bytestring-integers of arbitrary length  and for two s-complement signed integers by specifying signed True  See the docs for from bytes

User · Answer

You can also use the struct module to do this    gt  gt  gt  struct unpack   lt L    y xcc xa6 xbb   0  3148270713L

User · Answer

You can also use the struct module to do this    gt  gt  gt  struct unpack   lt L    y xcc xa6 xbb   0  3148270713L

User · Answer

int from bytes is the best solution if you are at version   3 2  The  struct unpack  solution requires a string so it will not apply to arrays of bytes  Here is another solution   def bytes2int  tb  order  big        if order     big   seq  0 1 2 3      elif order     little   seq  3 2 1 0      i   0     for j in seq  i    i lt  lt 8  tb j      return i   hex  bytes2int   0x87  0x65  0x43  0x21    returns  0x87654321    It handles big and little endianness and is easily modifiable for 8 bytes

User · Answer

A decently speedy method utilizing array array I ve been using for some time   predefined variables   offset   0 size   4 big   True   endian arr   array  B   arr fromstring   x00 x00 xff x00     5 bytes  encoding issues   0  0  195  191  0    to int   read   val   0 for v in arr offset offset size    pow -1 not big    val    val lt  lt 8  v   from int   write   val   16384 arr offset offset size          array  B    val gt  gt  i lt  lt 3   amp 255 for i in range size      pow -1 not big     It s possible these could be faster though   EDIT  For some numbers  here s a performance test  Anaconda 2 3 0  showing stable averages on read in comparison to reduce                               byte array to int py                           5000 iterations  threshold of min   5000ns                                        code           min              max              avg        efficiency                                                                                                                                       val   0  nfor v in arr  val    val lt  lt 8  v       5373 848ns     850009 965ns        8649 64ns    62 128                                                                                                                                                      val   reduce  shift  arr         6489 921ns    5094212 014ns      12040 269ns    53 902    This is a raw performance test  so the endian pow-flip is left out  The shift function shown applies the same shift-oring operation as the for loop  and arr is just array array  B   0 0 255 0   as it has the fastest iterative performance next to dict   I should probably also note efficiency is measured by accuracy to the average time

User · Answer

You can also use the struct module to do this    gt  gt  gt  struct unpack   lt L    y xcc xa6 xbb   0  3148270713L

User · Answer

As mentioned above using unpack function of struct is a good way  If you want to implement your own function there is an another solution   def bytes to int bytes       result   0     for b in bytes          result   result   256   int b  return result

User · Answer

gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  y xcc xa6 xbb    2043455163   Test 1  inverse    gt  gt  gt  hex 2043455163   0x79cca6bb    Test 2  Number of bytes   8    gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAAA    338822822454978555838225329091068225L   Test 3  Increment by one    gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAAB    338822822454978555838225329091068226L   Test 4  Append one byte  say  A     gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAABA    86738642548474510294585684247313465921L   Test 5  Divide by 256    gt  gt  gt  reduce lambda s  x  s 256   x  bytearray  AAAAAAAAAAAAAABA    256 338822822454978555838225329091068226L   Result equals the result of Test 4  as expected

User · Answer

import array integerValue   array array  I    y xcc xa6 xbb   0    Warning  the above is strongly platform-specific  Both the  I  specifier and the endianness of the string- int conversion are dependent on your particular Python implementation  But if you want to convert many integers strings at once  then the array module does it quickly

[python] How to convert a string of bytes into an int?

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