MicroPython 4x4 keypad on a Pico, GP13 to GP6

# A 4x4 keypad: rows on GP13 to GP10, columns on GP9 to GP6. keypad.py,
# in the next tab, scans it; each key is printed once per press.
import time
from keypad import Keypad

keys = Keypad(rows=(13, 12, 11, 10), cols=(9, 8, 7, 6))
print("Press a key")

while True:
    key = keys.scan()
    if key:
        print("key", key)
    time.sleep_ms(20)

# keypad.py: a 4x4 matrix keypad.
# Each row is driven high in turn; a held key joins its row to its column,
# so that column reads high. The columns are pulled down when nothing is held.
from machine import Pin
import time

KEYS = ("123A", "456B", "789C", "*0#D")

class Keypad:
    def __init__(self, rows, cols):
        self.rows = [Pin(n, Pin.OUT, value=0) for n in rows]
        self.cols = [Pin(n, Pin.IN, Pin.PULL_DOWN) for n in cols]
        self.last = None

    def held(self):
        for r, row in enumerate(self.rows):
            row.value(1)
            time.sleep_us(50)
            for c, col in enumerate(self.cols):
                if col.value():
                    row.value(0)
                    return KEYS[r][c]
            row.value(0)
        return None

    def scan(self):
        """The key just pressed, once per press, or None."""
        key = self.held()
        pressed = key if key != self.last else None
        self.last = key
        return pressed