How to convert signed to unsigned integer in python

Question

Let s say I have this number i   -6884376  How do I refer to it as to an unsigned variable  Something like  unsigned long i in C

User · Answer

Python doesn t have builtin unsigned types   You can use mathematical operations to compute a new int representing the value you would get in C  but there is no  unsigned value  of a Python int   The Python int is an abstraction of an integer value  not a direct access to a fixed-byte-size integer

User · Answer

You could use the struct Python built-in library   Encode   import struct  i   -6884376 print   0 b   format i    packed   struct pack   gt l   i     Packing a long number  unpacked   struct unpack   gt L   packed  0     Unpacking a packed long number to unsigned long print unpacked  print   0 b   format unpacked     Out    -11010010000110000011000 4288082920 11111111100101101111001111101000     Decode   dec pack   struct pack   gt L   unpacked     Packing an unsigned long number  dec unpack   struct unpack   gt l   dec pack  0     Unpacking a packed unsigned long number to long  revert action   print dec unpack    Out   -6884376      NOTE      gt  is BigEndian operation  l is long  L is unsigned long  In amd64 architecture int and long are 32bit  So you could use i and I instead of l and L respectively

User · Answer

Assuming    You have 2 s-complement representations in mind  and  By  unsigned long  you mean unsigned 32-bit integer    then you just need to add 2  32  or 1  lt  lt  32  to the negative value   For example  apply this to -1    gt  gt  gt  -1 -1  gt  gt  gt      2  32 4294967295L  gt  gt  gt  bin     0b11111111111111111111111111111111    Assumption  1 means you want -1 to be viewed as a solid string of 1 bits  and assumption  2 means you want 32 of them   Nobody but you can say what your hidden assumptions are  though   If  for example  you have 1 s-complement representations in mind  then you need to apply the   prefix operator instead   Python integers work hard to give the illusion of using an infinitely wide 2 s complement representation  like regular 2 s complement  but with an infinite number of  sign bits     And to duplicate what the platform C compiler does  you can use the ctypes module    gt  gt  gt  import ctypes  gt  gt  gt  ctypes c ulong -1     stuff Python s -1 into a C unsigned long c ulong 4294967295L   gt  gt  gt    value 4294967295L   C s unsigned long happens to be 4 bytes on the box that ran this sample

User · Answer

To get the value equivalent to your C cast  just bitwise and with the appropriate mask  e g  if unsigned long is 32 bit    gt  gt  gt  i   -6884376  gt  gt  gt  i  amp  0xffffffff 4288082920   or if it is 64 bit    gt  gt  gt  i  amp  0xffffffffffffffff 18446744073702667240   Do be aware though that although that gives you the value you would have in C  it is still a signed value  so any subsequent calculations may give a negative result and you ll have to continue to apply the mask to simulate a 32 or 64 bit calculation   This works because although Python looks like it stores all numbers as sign and magnitude  the bitwise operations are defined as working on two s complement values  C stores integers in twos complement but with a fixed number of bits  Python bitwise operators act on twos complement values but as though they had an infinite number of bits  for positive numbers they extend leftwards to infinity with zeros  but negative numbers extend left with ones  The  amp  operator will change that leftward string of ones into zeros and leave you with just the bits that would have fit into the C value   Displaying the values in hex may make this clearer  and I rewrote to string of f s as an expression to show we are interested in either 32 or 64 bits     gt  gt  gt  hex i   -0x690c18   gt  gt  gt  hex  i  amp    1  lt  lt  32  - 1    0xff96f3e8   gt  gt  gt  hex  i  amp    1  lt  lt  64  - 1   0xffffffffff96f3e8L    For a 32 bit value in C  positive numbers go up to 2147483647  0x7fffffff   and negative numbers have the top bit set going from -1  0xffffffff  down to -2147483648  0x80000000   For values that fit entirely in the mask  we can reverse the process in Python by using a smaller mask to remove the sign bit and then subtracting the sign bit    gt  gt  gt  u   i  amp    1  lt  lt  32  - 1   gt  gt  gt   u  amp    1  lt  lt  31  - 1   -  u  amp   1  lt  lt  31   -6884376   Or for the 64 bit version    gt  gt  gt  u   18446744073702667240  gt  gt  gt   u  amp    1  lt  lt  63  - 1   -  u  amp   1  lt  lt  63   -6884376   This inverse process will leave the value unchanged if the sign bit is 0  but obviously it isn t a true inverse because if you started with a value that wouldn t fit within the mask size then those bits are gone

User · Answer

Since version 3 2   def toSigned n  byte count      return int from bytes n to bytes byte count   little     little   signed True   output   In  8   toSigned 5  1                                                                                                                                                                                                                                                                                                       Out 8   5  In  9   toSigned 0xff  1                                                                                                                                                                                                                                                                                                    Out 9   -1

User · Answer

just use abs for converting unsigned to signed in python    a -12 b abs a  print b    Output     12

[python] How to convert signed to unsigned integer in python

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