Hexlify an integer in Python

Question

file_1 = (r'res\test.png')

with open(file_1, 'rb') as file_1_:
    file_1_read = file_1_.read()    
file_1_hex = binascii.hexlify(file_1_read)
print ('Hexlifying test.png..')

file_1_size_bytes = len(file_1_read)
file_1_size_bytes_hex = binascii.hexlify(file_1_size_bytes)

print (file_1_size_bytes_hex)

TypeError: 'int' does not support the buffer interface

Ok so im trying to hexlify the .png's byte length here. i know its because the len() of file_1_read is a number. im trying to convert decimal to hexidecimal. how would i go about doing that?

Maybe I am missing something, but what about hex? Integer in, hex-representation out. builtin and easy — Dave J
– Dave J, Commented Jan 17, 2015 at 13:41

falsetru · Accepted Answer · 2015-01-17 04:05:21Z

6

You can use str.format with x type:

>>> '{:x}'.format(123)
'7b'
>>> '{:08x}'.format(123)
'0000007b'

or using printf-style formatting:

>>> '%x' % 123
'7b'
>>> '%08x' % 123
'0000007b'

If you want to use binascii.hexlify, convert the int object to bytes using struct.pack:

>>> import struct
>>> import binascii
>>> struct.pack('i', 123)  # Replace 123 with `file_1_size_bytes`
b'{\x00\x00\x00'
>>> binascii.hexlify(struct.pack('i', 123))
b'7b000000'

You can control byte order using >, <, .. format specifier:

>>> binascii.hexlify(struct.pack('>i', 123))
b'0000007b'
>>> binascii.hexlify(struct.pack('<i', 123))
b'7b000000'

See Format characters - python struct module documentation

edited Jan 17, 2015 at 4:05

answered Jan 17, 2015 at 3:59

falsetru

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8 Comments

Death_Dealer Over a year ago

struct.pack( 'i', file_1_size_bytes) binascii.hexlify(struct.pack_into( '>i', file_1_size_bytes)) print (file_1_size_bytes_hex) So i was trying to pack the variable,im getting pack_into expected offset argument. whats the offset?

Death_Dealer Over a year ago

oops: / sorry i wrote that wrong. i included the assignment and im getting the same struct.error pack_into expected offset argument.

falsetru Over a year ago

@Death_Dealer, Use pack instead of pack_into. (pack_into accepts an addition buffer object as the second parameter) docs.python.org/3/library/struct.html#struct.pack_into

Death_Dealer Over a year ago

ok so that fixed that error, now im getting, file_test.write(file_1_size_bytes_hex) TypeError: must be str, not bytes.

falsetru Over a year ago

@Death_Dealer, unpack it, then pack it: struct.pack('>H', *struct.unpack('>I', b'\x00\x00\x00\x11')). IOW, convert it to int, then repack it.

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