pinout.vvzero.com/description/overlay/i2c.md

#I2C - Inter Integrated Circuit

The Raspberry Pi's I2C pins are an extremely useful way to talk to many different types of external peripheral; from the MCP23017 digital IO expander, to a connected ATmega.

You can verify the address of connected I2C peripherals with a simple one-liner:

sudo apt-get install i2c-tools
sudo i2cdetect -y 1

You can access i2c from Python using the smbus library:

sudo apt-get install python-smbus

And then in Python:

import smbus
DEVICE_BUS = 1
DEVICE_ADDR = 0x15
bus = smbus.SMBus(DEVICE_BUS)
bus.write_byte_data(DEVICE_ADDR, 0x00, 0x01)