NEWBIE: how to get text onto 2 lines on a 16x2 lcd display

[RobH]

On 26/09/2019 12:55, Rhodri James wrote:
> On 26/09/2019 11:58, RobH wrote:
>> Thanks, but was is Python REPR.
> 
> DL was referring to the interactive program you get when you type 
> "python" at a Linux or Windows command prompt.  Here's an example, 
> copied from my Linux box:
> 
> rhodri at scrote:~$ python
> Python 2.7.15+ (default, Jul  9 2019, 16:51:35)
> [GCC 7.4.0] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>  >>> import cgi
>  >>> help(cgi)
> [[screeds of documentation for the cgi module cut]]
>  >>> [[type control-D to get out]]
> rhodri at scrote:~$
> 
> (The bits in [[double square brackets]] are my comments, not something 
> either I or Python typed!)
> 
>> This my adaptation of non working code. Bodged from the char_lcd.py code:
>>
>>    GNU nano 2.7.4                          File: char_lcd.py
>>
>> #!/usr/bin/python
>> # Example using a character LCD connected to a Raspberry Pi or 
>> BeagleBone Black.
>> import time
>>
>> import Adafruit_CharLCD as LCD
> 
> Aha, that's the critical information we were lacking earlier.  I found 
> the Adafruit_CharLCD library after a little googling.  It's marked as 
> deprecated (the author now uses something else), but if it works for you 
> you might as well keep on using it.
> 
> [[Much set-up for the Pi cut for brevity]]
> 
>> # Initialize the LCD using the pins above.
>> lcd = LCD.Adafruit_CharLCD(lcd_rs, lcd_en, lcd_d4, lcd_d5, lcd_d6, 
>> lcd_d7,
>>                             lcd_columns, lcd_rows, lcd_backlight)
>>
>> # Print a two line message
>> # lcd.message('Hello\nworld!')
>> lcd.message( "Hello" 1)
> 
> It looks like lcd.message() takes a text string and displays on the LCD, 
> starting at the current cursor position (I'll get back to that).  You 
> optimistically added an extra argument, the line number to start at 
> (you're missing a comma, but that's an easy typo to make and I assume 
> you already caught it).  Unfortunately lcd.message() only takes the one 
> argument, the text string.  This is where that error message comes from: 
> "TypeError: message() takes exactly 2 arguments (3 given)" means that 
> you gave the function more arguments than it knew what to do with.
> 
> (Why 2 and 3 instead of 1 and 2?  "lcd" itself is an argument to 
> message(), telling it which lcd to send the message to if you had more 
> than one.  When you look at the function definition, you'll see that it 
> start with "def message(self, text):" which makes that a bit more 
> explicit.  Anyway, that's beside the point.)
> 
> So how do you control where you start your message on the LCD?  It looks 
> like the answer is the lcd.set_cursor() function.  The cursor is the 
> point from which your printing starts.  In your text editor it's 
> probably a blinking vertical line (or underscore, or blob... editors 
> vary).  On your LCD display it's probably invisible, though it looks 
> like there's another function to change that.
> 
> Anyway, you give set_cursor() a column number and a row number in that 
> order.  I think they start from 0, so to write "Hello" to the second 
> line of your display you would write:
> 
>    lcd.set_cursor(0, 1)
>    lcd.message("Hello")
> 
> The gotcha here is that message() is only going to write the characters 
> you tell it to, and won't overwrite anything else.  If for example you 
> followed up the two lines above with:
> 
>    lcd.set_cursor(0, 1)  # Back to the start of the line
>    lcd.message("Bye")
> 
> you would end up with "Byelo" displayed on the LCD.  You would need to 
> put extra spaces on the end of your message to overwrite the characters 
> you don't want any more, but not so many that you overwrite what you 
> want to keep.  Working out how many spaces that is for any given message 
> could be quite tedious.  You may well find it easier to lcd.clear() the 
> whole display and rewrite everything when you want to change anything.
> 
> Anyway, I hope that helps.
> 

Thank you, that does help me just great.
So simple as well. Actually I have worked quite a lot with Arduinos and 
the code or sketch for an lcd there is just the same to write to the 2nd 
line. I didn't think it would work for python, but it does!
Other lines like lcd.delay(1000) and lcd.begin(16,2), do not work in 
python, but I thought to try them to find out.

I am using a Raspberry Pi Zero for this little project, which now does 
what I want for now.

Thanks again.