Python how to write to a binary file

Question

I have a list of bytes as integers  which is something like   120  3  255  0  100    How can I write this list to a file as binary   Would this work   newFileBytes    123  3  255  0  100    make file newFile   open  filename txt    wb     write to file newFile write newFileBytes

User · Accepted Answer

This is exactly what bytearray is for   newFileByteArray   bytearray newFileBytes  newFile write newFileByteArray    If you re using Python 3 x  you can use bytes instead  and probably ought to  as it signals your intention better   But in Python 2 x  that won t work  because bytes is just an alias for str  As usual  showing with the interactive interpreter is easier than explaining with text  so let me just do that   Python 3 x    gt  gt  gt  bytearray newFileBytes  bytearray b   x03 xff x00d    gt  gt  gt  bytes newFileBytes  b   x03 xff x00d    Python 2 x    gt  gt  gt  bytearray newFileBytes  bytearray b   x03 xff x00d    gt  gt  gt  bytes newFileBytes    123  3  255  0  100

User · Answer

As of Python 3 2   you can also accomplish this using the to bytes native int method   newFileBytes    123  3  255  0  100    make file newFile   open  filename txt    wb     write to file for byte in newFileBytes      newFile write byte to bytes 1  byteorder  big      I e   each single call to to bytes in this case creates a string of length 1  with its characters arranged in big-endian order  which is trivial for length-1 strings   which represents the integer value byte  You can also shorten the last two lines into a single one   newFile write    join  byte to bytes 1  byteorder  big   for byte in newFileBytes

User · Answer

To convert from integers  lt  256 to binary  use the chr function   So you re looking at doing the following   newFileBytes  123 3 255 0 100  newfile open path  wb   newfile write     join chr i  for i in newFileBytes   encode  charmap

User · Answer

Use pickle  like this  import pickle  Your code would look like this   import pickle mybytes    120  3  255  0  100  with open  bytesfile    wb   as mypicklefile      pickle dump mybytes  mypicklefile    To read the data back  use the pickle load method

User · Answer

You can use the following code example using Python 3 syntax   from struct import pack with open  foo bin    wb   as file    file write pack   lt IIIII    bytearray  120  3  255  0  100       Here is shell one-liner   python -c   from struct import pack nwith open  foo bin    wb   as file  file write pack   lt IIIII    bytearray  120  3  255  0  100

User · Answer

Use struct pack to convert the integer values into binary bytes  then write the bytes  E g   newFile write struct pack  5B    newFileBytes     However I would never give a binary file a  txt extension   The benefit of this method is that it works for other types as well  for example if any of the values were greater than 255 you could use  5i  for the format instead to get full 32-bit integers

[python] Python how to write to a binary file?

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