Clever Geek Handbook

Python error in If-Then statement

I am writing a program in python that works like this:

  • Enter an input string through the serial port when hit enter (carriage return)
  • Mark $

    the first character of the input line, then continue if present
  • Delete all unnecessary characters and alphabets except numerics

    and ,

    , then print it.

Problem

The program gets stuck if a character is $

missing from the input line because next time if it receives an input line with $

it doesn't print the values

kindly review my codes below and tell me how to resolve it?

CODE

import serial,re

x = [0,0,0]
ser = serial.Serial('/dev/ttyAMA0', 9600)
buffer = ''

while True:
    buffer += ser.read(ser.inWaiting())
    if '\n' in buffer:
        if buffer[0] == '$':
            x= re.sub("[^0-9\,]","", buffer)
            x1 = x.rstrip()
            x2= x1.split(",")
            print((x2[0]),(x2[1]),(x2[2]))            
            buffer = ""
+3


source to share


2 answers


While it's not entirely obvious what the purpose of your code is, you can just remove the last line to clear the buffer every time, otherwise you keep adding to it and if it doesn't start with $

, it never will.



while True:
    buffer += ser.read(ser.inWaiting())
    if '\n' in buffer:
        if buffer[0] == '$':
            x= re.sub("[^0-9\,]","", buffer)
            x1 = x.rstrip()
            x2= x1.split(",")
            print((x2[0]),(x2[1]),(x2[2]))            
        buffer = ""
+2


source


The problem is that you keep adding new lines to the end of the buffer, freeing it only if you have a command. So, once you get a line that is not a command, your buffer will never be started with the command.

I think the riddle question is what you asked for.



But it still won't work correctly if you can get two lines (or worse, part of one line and part of the next) in the same buffer. So, you really want something more:

while True:
    buffer += ser.read(ser.inWaiting())
    lines = buffer.split('\n')
    for line in lines[:-1]:
        if line[0] == '$':
            x= re.sub("[^0-9\,]","", line)
            x1 = x.rstrip()
            x2= x1.split(",")
            print((x2[0]),(x2[1]),(x2[2]))            
    buffer = lines[-1]

split

splits the buffer into all full lines plus an empty line or the remaining partial line. So, you process full lines and insert the remaining blank line or partial line into a buffer that will be appended to the next read.

+2


source






More articles:


All Articles