MicroPython 7-segment digit on a Pico through a 74HC595

# One 7-segment digit through a 74HC595 (DS GP18, ST_CP GP20, SH_CP
# GP21): the hex digits 0 to F, one a second. The display is common
# anode, so a segment lights when its output is low: each pattern below
# has a 0 for every lit segment, in the order DP G F E D C B A.
import time
from hc595 import HC595

DIGITS = [0xC0, 0xF9, 0xA4, 0xB0, 0x99, 0x92, 0x82, 0xF8,
          0x80, 0x90, 0x88, 0x83, 0xC6, 0xA1, 0x86, 0x8E]

chip = HC595(ds=18, stcp=20, shcp=21)

while True:
    for n, pattern in enumerate(DIGITS):
        chip.write(pattern, msb_first=False)   # A goes out first, to Q7
        print("digit %X" % n)
        time.sleep(1)

# hc595.py: a 74HC595 shift register on three pins.
# Each bit goes out on DS and is clocked in on a rising SH_CP; a rising
# ST_CP then copies all eight to the outputs Q0 to Q7 at once.
from machine import Pin

class HC595:
    def __init__(self, ds, stcp, shcp, oe=None):
        self.ds = Pin(ds, Pin.OUT, value=0)
        self.stcp = Pin(stcp, Pin.OUT, value=0)
        self.shcp = Pin(shcp, Pin.OUT, value=0)
        if oe is not None:
            self.oe = Pin(oe, Pin.OUT, value=0)    # OE low: the outputs are on

    def shift(self, byte, msb_first=True):
        for i in range(8):
            bit = 7 - i if msb_first else i
            self.ds.value((byte >> bit) & 1)
            self.shcp.value(1)
            self.shcp.value(0)

    def latch(self):
        self.stcp.value(1)
        self.stcp.value(0)

    def write(self, byte, msb_first=True):
        self.shift(byte, msb_first)
        self.latch()