Writing an ASCII string as binary in python

Question

I have the string ASCII = "abcdefghijk". I want to write this to a binary file in binary format using python.

I tried the following:

str = "abcdefghijk" fp = file("test.bin", "wb") hexStr = "".join( (("\\x%s") % (x.encode("hex"))) for x in str) fp.write(hexStr) fp.close() 

However, when I open test.bin, I see the following in ascii format instead of binary.

 \x61\x62\x63\x64\x65\x66\x67 

I understand this because there are two abbreviations ("\\ x% s"). How can I solve this problem? Thanks in advance.

Update:

The following is the expected result:

 file = open("test.bin", "wb") file.write("\x61\x62\x63\x64\x65\x66\x67") file.close() 

But how can I achieve this with the string "abcdef" ASCII.

Answer 1

You misunderstood what \xhh does in Python strings. Using the \x notation in Python strings is just the syntax for creating specific code points.

You can use '\x61' to create a string, or you can use 'a' ; both are just two ways to tell me a character string with a hexadecimal value of 61, for example. ASCII character:

 >>> '\x61' 'a' >>> 'a' 'a' >>> 'a' == '\x61' True 

The syntax \xhh then is not a value; in the end result there are no characters \ and no x and no 6 and 1 .

You should just write your line:

 somestring = 'abcd' with open("test.bin", "wb") as file: file.write(somestring) 

There is nothing magical about binary files; the only difference with a file opened in text mode is that the binary will not automatically translate \n newlines to the line separator standard for your platform; for example, when writing to Windows, \n instead produces \r\n .

You certainly do not need to create hexadecimal escape sequences for writing binary data.

In Python 3, strings are Unicode data and cannot simply be written to a file without encoding, but in Python the str type is already encoded. So, in Python 3, you should use:

 somestring = 'abcd' with open("test.bin", "wb") as file: file.write(somestring.encode('ascii')) 

or you should use a byte string literal; b'abcd' .

Answer 2

I think that you do not necessarily understand what binary / ascii is ... all files are binary in the sense that its just bits. ascii is just a representation of some bits ... 99.9999% of file editors will display your bits as ascii if they can, and if there is no other encoding declared in the file itself ...

 fp.write("abcd") 

exactly equivalent

 fp.write("\x61\x62\x63\x64")