Python 2 3 Convert Integer to bytes Cleanly

Question

The shortest ways I have found are   n   5    Python 2  s   str n  i   int s     Python 3  s   bytes str n    ascii   i   int s    I am particularly concerned with two factors  readability and portability   The second method  for Python 3  is ugly   However  I think it may be backwards compatible   Is there a shorter  cleaner way that I have missed   I currently make a lambda expression to fix it with a new function  but maybe that s unnecessary

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In Python 3 x  you can convert an integer value  including large ones  which the other answers don t allow for  into a series of bytes like this   import math  x   0x1234 number of bytes   int math ceil x bit length     8    x bytes   x to bytes number of bytes  byteorder  big    x int   int from bytes x bytes  byteorder  big   x    x int

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I have found the only reliable  portable method to be  bytes bytearray  n      Just bytes  n   does not work in python 2   Taking the scenic route through bytearray seems like the only reasonable solution

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from int to byte   bytes string   int v to bytes  lenth  endian     where the lenth is 1 2 3 4      and endian could be  big  or  little   form bytes to int   data list   list  bytes

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You can use the struct s pack   In  11   struct pack   gt I   1  Out 11     x00 x00 x00 x01    The     is the byte-order  big-endian  and the  I  is the format character  So you can be specific if you want to do something else   In  12   struct pack   lt H   1  Out 12     x01 x00   In  13   struct pack  B   1  Out 13     x01    This works the same on both python 2 and python 3   Note  the inverse operation  bytes to int  can be done with unpack

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Converting an int to a byte in Python 3       n   5         bytes   n      gt  gt  gt  b  x05       guess that ll be better than messing around with strings  source  http   docs python org 3 library stdtypes html binaryseq

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Answer 1   To convert a string to a sequence of bytes in either Python 2 or Python 3  you use the string s encode method  If you don t supply an encoding parameter  ascii  is used  which will always be good enough for numeric digits   s   str n  encode      Python 2  http   ideone com Y05zVY Python 3  http   ideone com XqFyOj   In Python 2 str n  already produces bytes  the encode will do a double conversion as this string is implicitly converted to Unicode and back again to bytes  It s unnecessary work  but it s harmless and is completely compatible with Python 3   Answer 2   Above is the answer to the question that was actually asked  which was to produce a string of ASCII bytes in human-readable form  But since people keep coming here trying to get the answer to a different question  I ll answer that question too  If you want to convert 10 to b 10  use the answer above  but if you want to convert 10 to b  x0a x00 x00 x00  then keep reading   The struct module was specifically provided for converting between various types and their binary representation as a sequence of bytes  The conversion from a type to bytes is done with struct pack  There s a format parameter fmt that determines which conversion it should perform  For a 4-byte integer  that would be i for signed numbers or I for unsigned numbers  For more possibilities see the format character table  and see the byte order  size  and alignment table for options when the output is more than a single byte   import struct s   struct pack   lt i   5    b  x05 x00 x00 x00

[python] Python 2,3 Convert Integer to "bytes" Cleanly

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