Everything You Should Know About Python Serial Read

Serial ports are serial communication interfaces through which information is transferred sequentially one bit at a time. Parallel ports, on the other hand, transmit multiple bits simultaneously. The PySerial and functions like python serial read make communication with Serial Ports easier.

About the PySerial Package

Python on a computer with the PySerial package installed can communicate with external hardware. It is a useful package for problem solvers because it facilitates data exchange between computers and external hardware like voltmeters, flow meters, lights, and other devices that send information via ports.

Installing the Module

The PySerial package is NOT part of the Python Standard Library. Therefore, install manually. Anaconda Distributions of Python comes with the package pre-installed.

PIP Installation Command
$ pip install pyserial

Anaconda Prompt Command
> conda install pyserial

Importing the Module + Verifying Installation

After installing, the version can be verified with the following command.

import serial
print(serial.version)

About the Function

serial.read()

Arguments – Pass an integer value to specify the number of bytes to be returned.

Returns – Provides us a number of specified bytes

Using the Python serial read function to Fetch Information From Serial Ports

Python serial read is an important function of the module. It allows us to rake in the information that is provided from the ports. Here’s a Python implementation that helps us to do so.

with serial.Serial('/my/sample1', 3443, timeout=1) as serial:
     readOneByte = serial.read()          
     readTenByte = serial.read(10)        

Explanation

By default, .read() reads one byte at a time. By providing an integer value, you can set how many bytes of information are to be read by the function. 

Python Serial Read vs Readline

Using Serial Read + Write on Raspberry Pi

Ensure that your Raspberry Pi is up to date by running the following commands

sudo apt update
sudo apt upgrade

Reading Data

ser = serial.Serial(
        # Serial Port to read the data from
        port='/dev/ttyUSB0',

        #Rate at which the information is shared to the communication channel
        baudrate = 9600,
  
        #Applying Parity Checking (none in this case)
        parity=serial.PARITY_NONE,

       # Pattern of Bits to be read
        stopbits=serial.STOPBITS_ONE,
    
        # Total number of bits to be read
        bytesize=serial.EIGHTBITS,

        # Number of serial commands to accept before timing out
        timeout=1
)
# Pause the program for 1 second to avoid overworking the serial port
while 1:
        x=ser.readline()
        print x

Writing Data

import time
import serial

ser = serial.Serial(
        # Serial Port to read the data from
        port='/dev/ttyUSB0',

        #Rate at which the information is shared to the communication channel
        baudrate = 9600,
  
        #Applying Parity Checking (none in this case)
        parity=serial.PARITY_NONE,

       # Pattern of Bits to be read
        stopbits=serial.STOPBITS_ONE,
    
        # Total number of bits to be read
        bytesize=serial.EIGHTBITS,

        # Number of serial commands to accept before timing out
        timeout=1
)
counter=0

 
# Mentions the Current Counter number for each line written
# Pauses for one second each iteration to avoid overworking the port
while 1:
        ser.write("Write counter: %d \n"%(counter))
        time.sleep(1)
        counter += 1

Python Serial Read in Hex Format

Using the .hex() function we are storing the byte data in hex format in the variable hexData

import serial

ser = serial.Serial(
    port='/samplePort/ttyUSB1',
    baudrate=115200,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout = None
)

while 1:
    print ser.read()
    hexData= ser.read().hex()
    print hexData

Python pySerial in_waiting Function

This function can be used to retrieve the number of bytes in the input buffer.

Return(s) – Integer

Arguments – None

The function out_waiting() performs similarly. It provides the number of bytes in the output buffer.

Here’s an example program implementing the said function.

import serial
ser = serial.Serial(
    port = '/samplePort/myUSB',
    baudrate = 5000,
    parity = serial.PARITY_NONE,
    stopbits = serial.STOPBITS_ONE,
    bytesize = serial.EIGHTBITS,
    timeout=0.5, 
    inter_byte_timeout=0.1 
    )

# Reads one byte of information
myBytes = ser.read(1) 

# Checks for more bytes in the input buffer
bufferBytes = ser.inWaiting()

# If exists, it is added to the myBytes variable with previously read information
if bufferBytes:
    myBytes = myBytes + ser.read(bufferBytes)
    print(myBytes)

Python pySerial flush() function

flush() eliminates the contents of the internal buffer of a file object. It doesn’t take any arguments nor return anything. There are 2 types of flush functions:

• flushInput() – Clears Input Buffer
• flushOutput() – Clears Output Buffer
  

import serial
ser = serial.Serial('/samplePort/myUSB10')
# Clearing Input Buffer
ser.flushInput()

# Clearing Output Buffer
ser.flushOutput()
ser.write("get") 

# Pause for 100 milliseconds
sleep(.1)
print ser.read()

Reading Data From Arduino Boards using Python Serial Read

Arduino is an open-source electronics platform that provides easy-to-use hardware and software. Arduino boards can read inputs from sensors, a finger on a button, or a Twitter message, which they then output in the form of motors, LEDs, or even text.

import serial
import time

ser = serial.Serial('COM4', 9800, timeout=1)
time.sleep(2)

for i in range(50):
    # Reading all bytes available bytes till EOL
    line = ser.readline() 
    if line:
        # Converting Byte Strings into unicode strings
        string = line.decode()  
        # Converting Unicode String into integer
        num = int(string) 
        print(num)

ser.close()

Common Errors

Python AttributeError: 'module' object has no attribute 'Serial'

For this problem, try renaming your project file to ‘serial.py’. Delete serial.pyc if it exists. After that run import serial.

Furthermore, this problem occurs due to the fact that the package you’re importing has the same name as your project file.

FAQs on Python Serial Read

Conclusion

We learned that with the help of the PySerial Module and Python Serial Read we are able to handle information from devices via Serial Ports.