Controlling a motor on nodeMCU (ESP8266)

I have bought a CQRobot Metal DC Geared Motor w/Encoder with Metal Mounting Bracket -12V/40RPM /80Kg.cm

From the specs:

This is a Gear Motor w/Encoder, Support 6V and 12V working voltage, for Projects Such as Robot, Custom Servo, Arduino and 3D Printers.

The schematics suggested

The nodeMCU has this pinout

node MCU pinout

I used this nice class from OutOfCheeseError to control the motor.

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from machine import Pin, ADC, PWM

class DCMotor:
    def __init__(self, pwm_pin, direction_pin1, direction_pin2):
        """
        pwm_pin: PWM capable pin id. This pin should be connected to ENA/B.
        direction_pin1 and direction_pin1: Direction pins to be connected to
                                           N1/2 or N3/4.
        """
        self.dir_pin1 = Pin(direction_pin1, mode=Pin.OUT)
        self.dir_pin2 = Pin(direction_pin2, mode=Pin.OUT)
        self.pwm_pin = Pin(pwm_pin, mode=Pin.OUT)
        self.pwm = PWM(self.pwm_pin, freq=100, duty=0)

    def forward(self):
        self.dir_pin1.on()
        self.dir_pin2.off()

    def backward(self):
        self.dir_pin1.off()
        self.dir_pin2.on()

    def stop(self):
        self.dir_pin1.off()
        self.dir_pin2.off()

    def set_speed(self, ratio):
        """
        sets speed by pwm duty cycle value.
        ratio: The speed ratio ranging from 0 to 1.
               Anything above 1 will be taken as 1 and negative
               as 0.
        """
        if ratio < 0:
            self.pwm.duty(0)
        elif ratio <= 1.0:
            self.pwm.duty(int(1024*ratio))
        else:
            self.pwm.duty(1024)

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# D1,D2, D3
motor = DCMotor(5, 4, 0)

print("forward")
motor.forward()
motor.set_speed(0)
sleep(5)
motor.set_speed(0.5)

print("backward")
sleep(5)
motor.backward()
motor.set_speed(1)

print("stop")
sleep(2)
motor.set_speed(0)
motor.stop()