Display CPU temperature on CrowPi2 7-segment display

import time
from Adafruit_LED_Backpack import SevenSegment

# Digit value to bitmask mapping:
DIGIT_VALUES = {
    ' ': 0x00,
    '-': 0x40,
    '0': 0x3F,
    '1': 0x06,
    '2': 0x5B,
    '3': 0x4F,
    '4': 0x66,
    '5': 0x6D,
    '6': 0x7D,
    '7': 0x07,
    '8': 0x7F,
    '9': 0x6F,
    'A': 0x77,
    'B': 0x7C,
    'C': 0x39,
    'D': 0x5E,
    'E': 0x79,
    'F': 0x71
}

# ===========================================================================
# display cpu temperature
# ===========================================================================
segment = SevenSegment.SevenSegment(address=0x70)

# Initialize the display. Must be called once before using the display.
segment.begin()

while(True):
        segment.clear()
        with open("/sys/class/thermal/thermal_zone0/temp", "r") as f:
            line = f.readline()
            for pos in range(4):
                c = line[pos]
                if c:
                    segment.buffer[pos*2] = DIGIT_VALUES.get(str(c).upper())
        segment.write_display()
        time.sleep(0.25)