unsigned char array from int array in python

Question

I try to define a new character (a capital german umlaut "Ä") on my 2004 lcd on a raspberry pi using wiringPi's lcdCharDef()

This is my code

import wiringpi2 as wiringpi
# Ä
cap_umlaut_a = [
 int('0b01010', 2),
 int('0b00100', 2),
 int('0b01010', 2),
 int('0b10001', 2),
 int('0b11111', 2),
 int('0b10001', 2),
 int('0b10001', 2),
 int('0b00000', 2)
]
print(cap_umlaut_a) # [10, 4, 10, 17, 31, 17, 17, 0]
wiringpi.lcdCharDef(lcd_handle, 0, cap_umlaut_a)

When I run this code I get the following error:

TypeError: in method 'lcdCharDef', argument 3 of type 'unsigned char [8]'

I expected these ints to be the same as unsigned chars

[edit]
In a different part of the code I use ord(char) to convert only one character to an unsigned int. Can this lead to the correct anser?

How can I cast/convert the array to a type that can be accepted?

P.S. (Note that (as far as I understand it) the python wiringPi library simply wraps the C functions of wiringPi)

[edit]
I opened an issue on github: https://github.com/WiringPi/WiringPi2-Python/issues/20

• speendo: you mean something like wiringpi.lcdCharDef(self.lcd_handle, 0, array.array('B',cap_umlaut_a))? Sorry, that gives me the same error...
• Patrick Maupin: Have you tried using chr() or byte() instead of int()? Also, you will need to join them together into a string (python 2) or byte string (python 3) and then decode() them into the Unicode you want. But why not just use the Unicode \Uxxxxx definition?
• speendo: @PatrickMaupin I think the Unicode would not work, as I have to define the pixels of the new character myself (the Hitachi HD44780U LCDs are not very smart - they don't know capital umlauts themselves). Or did I get you wrong? However, chr() did not work and byte() is not a built-in type in python
• Patrick Maupin: chr() doesn't take a string, but it would take your actual number...
• WorldSEnder: Maybe it takes a bytestring. can you try wiringpi.lcdCharDef(self.lcd_handle, 0, struct.pack('8B', *cap_umlaut_a))

Answer 1

I did a bit of research and found the source of the relevant python binding at this github repo.

The line in question is

res3 = SWIG_ConvertPtr(obj2, &argp3,SWIGTYPE_p_unsigned_char, 0 | 0 );

as you can see, you have to pass in the python equivalent of a pointer to unsigned char. According to this thread, the equivalent is a byte-string. This means that the correct call would be

import struct
wiringpi.lcdCharDef(lcd_handle, 0, struct.pack('8B', *cap_umlaut_a))

which should be equivalent to

wiringpi.lcdCharDef(lcd_handle, 0, b'\x0A\x04\x0A\x11\x1F\x11\x11\x00')

• speendo: Thank you for the answer. I really appreciate that! I just tried it. wiringpi.lcdCharDef(self.lcd_handle, 0, b'\x0A\x04\x0A\x11\x1F\x11\x11\x0') gives an error "ValueError: invalid \x escape" and wiringpi.lcdCharDef(lcd_handle, 0, struct.pack('8B', *cap_umlaut_a)) gives "struct.error: pack requires exactly 8 arguments"
• WorldSEnder: I fixed the first error, but I can't reproduce the second one (with the definitions from your question)
• speendo: hm. thanks for fixing the first one - I've seen it myself now :) now I also get the TypeError here... Maybe there is something else wrong in my code. I will try to make a running minimal example tomorrow and either post it or accept your answer, if I can locate the mistake.
• speendo: ... well, who needs sleep anyway. I just created the minimal example. Still get the same error. You can find it here: gist.github.com/anonymous/0fd82d376cd22763faf1
• WorldSEnder: @speendo, can you try with a normal string instead of a byte string? :<