ICD2O explained: the Grade 10 digital technology course, and what happened to ICS2O

# Can people read this text? A colour contrast checker (ours)
# Formula: WCAG 2.1 relative luminance and contrast ratio (w3.org/TR/WCAG21)
import csv
import io

PAIRS = """text,background
#000000,#FFFFFF
#777777,#FFFFFF
#30520C,#FBF8F2
#FFFF00,#FFFFFF
"""

def channel(value):
    """One 0 to 255 colour channel, turned into linear light."""
    c = value / 255
    if c <= 0.04045:
        return c / 12.92
    return ((c + 0.055) / 1.055) ** 2.4

def luminance(hex_colour):
    r = int(hex_colour[1:3], 16)
    g = int(hex_colour[3:5], 16)
    b = int(hex_colour[5:7], 16)
    return 0.2126 * channel(r) + 0.7152 * channel(g) + 0.0722 * channel(b)

def contrast(a, b):
    lighter = max(luminance(a), luminance(b))
    darker = min(luminance(a), luminance(b))
    return (lighter + 0.05) / (darker + 0.05)

for row in csv.DictReader(io.StringIO(PAIRS)):
    ratio = contrast(row["text"], row["background"])
    if ratio >= 4.5:
        verdict = "passes for body text"
    else:
        if ratio >= 3:
            verdict = "large text only"
        else:
            verdict = "fails"
    print(row["text"], "on", row["background"], round(ratio, 2), verdict)

Output: #000000 on #FFFFFF 21.0 passes for body text; #777777 on #FFFFFF 4.48 large text only; #30520C on #FBF8F2 8.47 passes for body text; #FFFF00 on #FFFFFF 1.07 fails. The third pair is this page’s own accent colour on its paper background.

# The modification: four levels instead of three (ours)

def verdict(ratio):
    if ratio >= 7:
        return "passes the enhanced level"
    elif ratio >= 4.5:
        return "passes for body text"
    elif ratio >= 3:
        return "large text only"
    return "fails"

for r in (21.0, 8.47, 4.48, 1.07, 7.0, 4.5, 3.0):
    print(r, verdict(r))

Output, in order: passes the enhanced level for 21.0, 8.47 and 7.0; large text only for 4.48 and 3.0; fails for 1.07; passes for body text for 4.5. The boundary values 7.0, 4.5 and 3.0 are there on purpose: at least means greater than or equal to.

print(7 + 3 * 2 ** 2)
print((7 + 3) * 2 ** 2)

What two numbers are printed?

x = "4" + "2"
print(x, type(x).__name__)
print(int("4") + int("2"))

What is printed on each line, and why are they different?

temp = -12
if temp < 0:
    if temp < -10:
        print("Extreme cold warning")
    else:
        print("Below freezing")
else:
    print("Above freezing")

What is printed? What would print if temp were -5? And if it were exactly 0, is the message right?

word = "Winnipeg"
print(len(word), word[0], word[-1], word.upper())

What four things are printed?

score = 0
for answer in ["b", "a", "c", "b"]:
    if answer == "b":
        score = score + 1
print(score)

What is printed? Describe in words what the program counts.

score = 7
print("Score: " + score)

This stops with an error. What kind of error, what does the message mean, and how do you fix it?