PySerial: Working with COM Ports in Python

Introduction

Serial port communication remains essential in industrial, IoT, robotics, and microcontroller systems. Controlling devices via COM (RS-232/RS-485/USB-Serial) requires a stable, cross-platform, and flexible tool. In Python, the go-to solution is the PySerial library.

PySerial provides a simple yet powerful interface for connecting, configuring, and transferring data over serial lines. It's widely used to communicate with Arduino, Raspberry Pi, modems, GPS receivers, controllers, sensors, and many other devices.

About PySerial

PySerial is a cross-platform Python library for working with serial ports. Created by Chris Liechti, it has become the de facto standard for serial communication in the Python ecosystem. The library supports Windows, Linux, macOS, and many other operating systems.

Key Features of PySerial

The library provides a unified API for working with various types of serial connections. It automatically handles platform-specific port operations and gives developers a clean, straightforward interface.

PySerial supports not only physical COM ports but also virtual connections, including USB-to-Serial adapters, Bluetooth Serial Port Profile, and even network connections via the RFC2217 protocol.

Installation and Setup

Install the library using the pip package manager:

pip install pyserial

Import the library in your Python script with a standard import statement:

import serial

Basic Workflow Architecture

Connection Lifecycle

Typical PySerial usage follows a simple pattern:

1. Create a Serial object — initialize with port parameters
2. Open the connection — establish communication with the device
3. Exchange data — send commands and read responses
4. Close the connection — properly terminate the session

ser = serial.Serial('COM3', baudrate=9600, timeout=1)
ser.write(b'command')
data = ser.readline()
ser.close()

Key Configuration Parameters

When creating a Serial object, you can set many parameters:

• port — device name (COM1, /dev/ttyUSB0, /dev/ttyAMA0)
• baudrate — data transfer speed (typically 9600, 38400, 115200)
• bytesize — character size in bits (5, 6, 7, 8)
• parity — parity checking (PARITY_NONE, PARITY_EVEN, PARITY_ODD)
• stopbits — number of stop bits (1, 1.5, 2)
• timeout — read operation timeout in seconds

Reading Data Methods

Basic Reading Methods

PySerial offers several ways to read data from the port:

Serial.read(size=1) — reads exactly the specified number of bytes. If not enough data is available, the method blocks until all bytes are received or the timeout expires.

data = ser.read(10)  # Read 10 bytes

Serial.readline() — reads data until a newline character (\n). This is the most popular method for text-based protocols.

line = ser.readline().decode('utf-8').strip()

Serial.read_all() — reads all available data from the input buffer immediately.

all_data = ser.read_all()

Advanced Reading Methods

Serial.read_until(expected) — reads data until a specified delimiter is encountered.