Python: Strange extra f added to bytes object

Question

I am using python and pyserial to talk to an embedded pic processor in a piece of scientific equipment. I sometimes find the when I construct the bytes object to write it adds an extra f to the first byte.

For example if I have bx03x66x02x01xaaxbb it evaluates to bx03fx02x01xaaxbb, which doesnt even seem valid. Can anyone shine some light this?

Comments

"f" is the same as x66; nothing has been changed.

Answer 1

 >>> b'x66' == b'f'
True

Python always prints a bytestring the same way. It doesn't 'remember' how it was originally created. Another example:

 >>> b'x68x65x6cx6cx6fx20x77x6fx72x6cx64'
b'hello world'

Answer 2

b'x66' == b'f' . The hex for "f" is 66. The f isn't inserted, it's the second byte of your string. When Python displays a string, is uses the ASCII character if it can, and a hex escape if it can't. When you use a hex value that is a valid ASCII character, it will display the character.