Sample code to display decimal numbers on a 4-digit 7-segment display

display_decimals.py

# code modified, tweaked and tailored from code at
# http://raspi.tv/2015/how-to-drive-a-7-segment-display-directly-on-raspberry-pi-in-python
import RPi.GPIO as GPIO
import random
import time

NUMBER_OF_DIGITS = 4

def format_num(num):
    digits_left = NUMBER_OF_DIGITS
    format_str = ''
    if num < 0:
        digits_left -= 1
        format_str += '-'
        num *= -1
    if isinstance(num, int):
        len_int = len(str(num))
    else:
        len_int = len(str(int(round(num))))
    if len_int > digits_left:
        return ''
    else:
        if isinstance(num, int):
            format_str += '%d'
        else:
            len_frac = digits_left - len_int
            format_str += '%%.%df' % len_frac
    return format_str % num


GPIO.setmode(GPIO.BCM)
 
# GPIO ports for the 7seg pins
segments = (11,4,23,8,7,10,18,25)
# 7seg_segment_pins (11,7,4,2,1,10,5,3) +  100R inline
 
for segment in segments:
    GPIO.setup(segment, GPIO.OUT)
    GPIO.output(segment, 0)
 
# GPIO ports for the digit 0-3 pins 
digits = (22,27,17,24)
# 7seg_digit_pins (12,9,8,6) digits 0-3 respectively
 
for digit in digits:
    GPIO.setup(digit, GPIO.OUT)
    GPIO.output(digit, 1)
 
num = {
    ' ':(0,0,0,0,0,0,0),
    '-':(0,0,0,0,0,0,1),
    '0':(1,1,1,1,1,1,0),
    '1':(0,1,1,0,0,0,0),
    '2':(1,1,0,1,1,0,1),
    '3':(1,1,1,1,0,0,1),
    '4':(0,1,1,0,0,1,1),
    '5':(1,0,1,1,0,1,1),
    '6':(1,0,1,1,1,1,1),
    '7':(1,1,1,0,0,0,0),
    '8':(1,1,1,1,1,1,1),
    '9':(1,1,1,1,0,1,1)
}

RAND_MAX = (10 ** NUMBER_OF_DIGITS) - 1
RAND_MIN = (-10 ** (NUMBER_OF_DIGITS - 1)) + 1

r = random.uniform(-1, 1)
max_scale = NUMBER_OF_DIGITS
if r < 0:
    max_scale -= 1
n = r * (10 ** random.randint(0, max_scale))
print(n)
next_mode = 'int'
last_change = time.time()

try:
    while True:
        s = format_num(n).rjust(NUMBER_OF_DIGITS)
        digit = 0
        for char in s:
            if char == '.':
                continue
            for loop in range(0,7):
                GPIO.output(segments[loop], num[char][loop])
                if digit < (NUMBER_OF_DIGITS-1) and s[digit+1] == '.':
                    GPIO.output(25, 1)
                else:
                    GPIO.output(25, 0)
            GPIO.output(digits[digit], 0)
            time.sleep(0.001)
            GPIO.output(digits[digit], 1)
            digit += 1
        if (time.time() - last_change) > 2:
            r = random.uniform(-1, 1)
            max_scale = NUMBER_OF_DIGITS
            if r < 0:
                max_scale -= 1
            n = r * (10 ** random.randint(0, max_scale))
            if next_mode == 'int':
                n = int(n)
                next_mode = 'float'
            elif next_mode == 'float':
                next_mode = 'int'
            print(n)
            last_change = time.time()
finally:
    GPIO.cleanup()