The Python os module reads operating-system environment variables so a robot can take configuration from its shell instead of hard-coded values. Use os.environ for a required setting; a missing key raises KeyError. Use os.environ.get(name, default) when a setting is optional, then convert the returned string to the type the program needs. section 3.5
Tune motor power from the environment
Read right and left motor adjustments with defaults of '1', convert them with float(), and store them in an ADJUST dictionary. A set_throttle function multiplies each requested throttle value by its adjustment, allowing wheel-specific tuning without requiring both variables to be set. section 3.5
Listing 3.2 envforward.py: Reading configuration values from environment variables
#!/usr/bin/env python3
from adafruit_crickit import crickit
import time
import os
DC_ADJUST_R = float(os.environ.get('ROBO_DC_ADJUST_R', '1'))
DC_ADJUST_L = float(os.environ.get('ROBO_DC_ADJUST_L', '1'))
ADJUST = dict(R=DC_ADJUST_R, L=DC_ADJUST_L)
MOTOR = dict(R=crickit.dc_motor_1, L=crickit.dc_motor_2)
def set_throttle(name, value):
MOTOR[name].throttle = value * ADJUST[name]
def forward():
set_throttle('R', 0.9)
set_throttle('L', 0.9)
time.sleep(0.2)
set_throttle('R', 0)
set_throttle('L', 0)
forward()
This runnable script reads optional ROBO_DC_ADJUST_R and ROBO_DC_ADJUST_L values, applies them to named motors, and drives forward. section 3.5
