The rtkmcb Python library allows you to independently control left and right motors, in addition to controlling both at once with a variety of, hopefully, intuitive commands;
# Move forwards at speed 0 ( stopped ) to 100
mcb.left_motor.forwards( speed )
# Move backwards at speed 0 ( stopped ) to 100
mcb.left_motor.backwards( speed )
# Set speed of the motor from -100 ( full reverse ) to 100 ( full forward )
mcb.left_motor.speed( speed )
# Stop
mcb.left_motor.stop()
All of these also work for the "right_motor"
# Set speed of both motors from -100 to 100
mcb.speed( speed )
# Alternatively, set speed independently
mcb.speed( left_speed, right_speed )
# Turn left
mcb.left( speed )
# Turn right
mcb.right( speed )
# Turn -100 left to 100 right
mcb.turn( speed )
# Stop
mcb.stop()