MicroPython four-digit display, multiplexed, on an ESP32-DevKitC V4

# Four digits, one 74HC595: the chip sets the segments and GPIO 25, 26,
# 27 and 14 pick which digit is on. Each digit is lit for a moment in
# turn, fast enough that all four look lit: 0123.
from machine import Pin
from hc595 import HC595
import time

chip = HC595(15, 2, 4)
digits = [0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e]
select = [Pin(n, Pin.OUT, value=0) for n in (25, 26, 27, 14)]
show = [0, 1, 2, 3]
frames = 0

while True:
    for place, n in enumerate(show):
        chip.write(0xff, msb_first=False)     # blank, so no ghost of the last digit
        for i, s in enumerate(select):
            s.value(1 if i == place else 0)
        chip.write(digits[n], msb_first=False)
        time.sleep_ms(1)
    frames += 1
    if frames % 200 == 0:
        print("showing 0123")

# hc595.py: send a byte to a 74HC595 on three pins.
# data is DS, latch is ST_CP and clock is SH_CP. Each bit is set on DS
# and clocked in on a rising SH_CP; a rising ST_CP shows all eight.
from machine import Pin

class HC595:
    def __init__(self, data, latch, clock, oe=None):
        self.data = Pin(data, Pin.OUT, value=0)
        self.latch = Pin(latch, Pin.OUT, value=0)
        self.clock = Pin(clock, 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, value, msb_first=True):
        for i in range(8):
            bit = 7 - i if msb_first else i
            self.data.value((value >> bit) & 1)
            self.clock.value(1)
            self.clock.value(0)

    def write(self, value, msb_first=True):
        self.latch.value(0)
        self.shift(value, msb_first)
        self.latch.value(1)