How to format Python String for particular POS printer

Question

I am using a Thermal Receipt Printer POS-8330 found HERE

I am writing code that sends a python string to the printer, here is the code that accomplishes this

Answer 1

Looking at the manual, this printer uses control characters (the first 32 characters in ASCII) to start commands and separate them from text.

So you can intersperse text and printer commands. Just make sure to open the output file in binary mode!

For example, looking at page 17 of the programming manual, the command ESC @ resets the printer. This command consists of two characters (bytes); decimal 27 followed by decimal 64. You can create that command as follows:

In [7]: bytes([27,64])
Out[7]: b'\x1b@'

You have to set the left margin (command GS L, page 37) and the printing area width (command GS W, page 38). Note that "horizontal motion units" is explained in the GS P command on page 38. The default horizontal motion unit is 25.4/180 = 0.1411 mm or 1/180 = 0.0055 inches.

So if you want to set the left margin to approximately 5 mm (4.94 mm to be precise), you have to send the following command:

dIn [14]: bytes([29, 76, 35,0])
Out[14]: b'\x1dL#\x00'

The value 35 is calculated like this:

In [13]: round(5/(25.4/180))
Out[13]: 35

If you also want to set the printing width to 60 mm, then the argument for the GS W command would have to be:

In [15]: round(60/(25.4/180))
Out[15]: 425

This is larger than 255, so it would have to be spread over two bytes;

In [17]: 425-256
Out[17]: 169

The command would be:

In [18]: bytes([29, 87, 169,1])
Out[18]: b'\x1dW\xa9\x01'

You can combine these commands, I think:

In [20]: bytes([29, 76, 35, 0, 29, 87, 169,1])
Out[20]: b'\x1dL#\x00\x1dW\xa9\x01'

Edit:

Adding the print commands to the data is easy:

printdata = b'\x1dL#\x00\x1dW\xa9\x01' + finalString.encode('utf-8')

Note that you do need to encode the string, since the printer commands are binary.

Also note that you need to write the string to a file in binary mode.

with open(self.filename, "wb") outf:
    outf.write(printdata)
os.startfile(self.filename, "print")

Finally, I used with so that the file is properly closed after writing. The way you are using it leaves the file open.