from machine import Pin
from utime import sleep

led1 = Pin(0, Pin.OUT)
led2 = Pin(1, Pin.OUT)
led3 = Pin(2, Pin.OUT)
led4 = Pin(3, Pin.OUT)

while True:
    led4.value(0)
    led3.value(0)
    led2.value(0)
    led1.value(0)
    sleep(1)

    led4.value(0)
    led3.value(0)
    led2.value(0)
    led1.value(1)
    sleep(1)

    led4.value(0)
    led3.value(0)
    led2.value(1)
    led1.value(0)
    sleep(1)

    led4.value(0)
    led3.value(0)
    led2.value(1)
    led1.value(1)
    sleep(1)

    led4.value(0)
    led3.value(1)
    led2.value(0)
    led1.value(0)
    sleep(1)

    led4.value(0)
    led3.value(1)
    led2.value(0)
    led1.value(1)
    sleep(1)

    led4.value(0)
    led3.value(1)
    led2.value(1)
    led1.value(0)
    sleep(1)

    led4.value(0)
    led3.value(1)
    led2.value(1)
    led1.value(1)
    sleep(1)

    led4.value(1)
    led3.value(0)
    led2.value(0)
    led1.value(0)
    sleep(1)

    led4.value(1)
    led3.value(0)
    led2.value(0)
    led1.value(1)
    sleep(1)

    led4.value(1)
    led3.value(0)
    led2.value(1)
    led1.value(0)
    sleep(1)

    led4.value(1)
    led3.value(0)
    led2.value(1)
    led1.value(1)
    sleep(1)

    led4.value(1)
    led3.value(1)
    led2.value(0)
    led1.value(0)
    sleep(1)

    led4.value(1)
    led3.value(1)
    led2.value(0)
    led1.value(1)
    sleep(1)

    led4.value(1)
    led3.value(1)
    led2.value(1)
    led1.value(0)
    sleep(1)

    led4.value(1)
    led3.value(1)
    led2.value(1)
    led1.value(1)
    sleep(1)



'''
#Efficient 4-bit Binary-counting LEDs (from PDF)
from machine import Pin
from utime import sleep
 
PORT = [3,2,1,0]                    # port connections
DIR = ["0","0","0","0"]             # port directions
L= [0]*4

#This functions configures the port pins as outputs ("O") or as inputs ("I") 
def configure_port():
    for i in range(0,4):
        if DIR[i] == "0":
            L[i] = Pin(PORT[i],Pin.OUT)
        else:
            L[i] = Pin(PORT[i],Pin.IN)
    return

#This function sends 4-bit data (0 to 15) to the PORT 
def port_output(x):
    b = bin(x)                      # convert into binary
    b = b.replace("0b","")          # remove leading "0b"
    diff = 4 - len(b)               # find the length
    for i in range(0,diff):
        b = "0" + b                 # insert leading os

    for i in range(0,4):
        if b[i] == "1":
            L[i].value(1)
        else:
            L[i].value(0)
    return
 
configure_port()                    # configure port to all outputs

#Main program loop :- Count up in binary every second 
cnt = 0
while True:
    port_output(cnt)                # send cnt to port
    sleep(1)                        # wait 1 second
    cnt = cnt + 1                   # increment cnt
    if cnt > 15:
        cnt = 0
'''


'''
# Optimised Code by Manaswini Ray
from machine import Pin
from utime import sleep
 
led1 = Pin(0,Pin.OUT)
led2 = Pin(1,Pin.OUT)
led3 = Pin(2,Pin.OUT)
led4 = Pin(3,Pin.OUT)
 
led_pins = [led1, led2, led3, led4]

while True:
    for i in range(16):
        for j in range(4):
            led_pins[j].value(i & 1)
            i>>=1
        sleep(1)
'''