PCAP Strings Practice Question
Which of the following is the correct way to format a string to include a variable value with two decimal places in Python?
⚠ Common exam trap
The Python Institute often tests the distinction between the width specifier (e.g., `:2f`) and the precision specifier (e.g., `:.2f`), so candidates mistakenly choose Option D thinking `:2f` means two decimal places, when it actually sets a minimum field width of 2 characters.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
f"{value:.2f}"
Uses the correct f-string format specifier `:.2f`, where `f` stands for fixed-point notation and `.2` specifies two decimal places. This is the standard Python syntax for formatting a floating-point number to two decimal places within an f-string.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
f"{value:.2f}"
Why this is correct
Correct. The format specifier `.2f` is a dot (precision marker) followed by `2` (the number of digits) and the fixed-point type `f`. This tells Python to render `value` as a float rounded to exactly two decimal places, so 3.14159 becomes `3.14`. This is the official way to force a fixed number of digits after the decimal point in f-string formatting.
- ✗
f"{value:.2}"
Why it's wrong here
Incorrect because omitting the type suffix `f` causes Python to fall back to the default `g` format. With `g`, the precision `2` is interpreted as two significant digits, not two digits after the decimal point; for instance, 12.345 becomes `12` rather than `12.35`. To display a fixed number of decimal places, you must explicitly include a float type such as `f` after the precision.
- ✗
f"{value%:.2f}"
Why it's wrong here
Incorrect because the percent sign appears before the colon, so Python parses `value%` as the expression part of the f-string and attempts to evaluate a modulo operation with no right-hand operand, producing a `SyntaxError`. To display a percentage, the `%` must come after the precision as the type suffix, e.g., `f"{value:.2%}"`, which multiplies the value by 100 and appends a percent sign.
- ✗
f"{value:2f}"
Why it's wrong here
Incorrect because the digit `2` is not preceded by a dot, so the format spec parser treats it as a minimum field width rather than a precision. In `2f`, `width=2` and `type=f`, meaning the value is printed with the default six decimal places and only padded to a minimum width of two characters—not rounded to two decimals. A precision must be written with a leading dot, as in `.2f`.
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