Read it before you run it
A friend writes 10 - 4 / 2 and says the answer is 3. Is your friend right?
A good programmer can read code and say the answer before running it. This is the skill of interpreting code. It also helps you find bugs.
Key words
| Word | What it means | Example |
|---|---|---|
| Interpret | Read code and work out what it does. | say what 7 // 2 gives |
| Debug | Find and fix mistakes. | change = to == |
| Trace table | A table where you write each value after every step. | step, value |
| Operator | A symbol that does something to values. | + |
| Relational operator | An operator that compares two values. | >= |
| Boolean operator | And, or, not. They join True and False values. | a and b |
| Logic error | The program runs and gives a wrong answer. | > instead of >= |
The cells students fill in are left blank in this preview.
Is your friend right?
Have a go
Is your friend right?
3 questionsHave a go: your answers are marked here and then forgotten. Sign in if you would like your score kept, and to pick up where you left off.Sign in to keep your score
Your answers are marked here and are not kept. A college account keeps every student’s marks.
Worked example: trace an expression
| Step | What Python does | Value so far |
|---|---|---|
| Code | `result = 7 // 2 + 7 % 2 * 3` | |
| 1 | 7 // 2 is the whole part of 7 divided by 2 | 3 |
| 2 | 7 % 2 is the remainder | 1 |
| 3 | 1 * 3 (multiply before add) | 3 |
| 4 | 3 + 3 | 6 |
| Result | result is 6 | 6 |
The cells students fill in are left blank in this preview.
Try it: predict, then run
a = 7 // 2 + 7 % 2 * 3
b = (2 + 3) * 4 - 1
c = 5 > 3 and not 2 > 4
d = 17 % 5 == 2
print(a)
print(b)
print(c)
print(d)
# Write your predictions on paper first.
# Then run it and check.
Interpret the code
Have a go
Interpret the code
4 questionsHave a go: your answers are marked here and then forgotten. Sign in if you would like your score kept, and to pick up where you left off.Sign in to keep your score
Your answers are marked here and are not kept. A college account keeps every student’s marks.