f-strings & String Formatting

Almost every program eventually needs to weave data into text — a greeting with the user's name, a receipt with a price, a log line with a timestamp. f-strings are Python's clean, fast, and readable way to do exactly that.

Learn f-strings & String Formatting in our free Python course — a beginner-friendly interactive lesson with runnable examples, a practice exercise and a…

Part of the free Python course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

By the end of this lesson you'll format money, percentages, tables, and dates like a professional, and you'll understand the format spec mini-language that powers it all.

An f-string (formatted string literal) is a normal string with the letter f placed right before the opening quote. Inside it, anything you wrap in curly braces {' '} is treated as Python code, evaluated, and slotted into the text.

Notice you never call str() inside an f-string — Python converts each value to text for you automatically. That single feature removes a whole category of TypeError bugs.

The same line of output, written three ways. Read each and decide which one you'd want to maintain at 2am during an outage:

The braces are not limited to bare variable names. You can do arithmetic, call methods, index into a list, or even run a small conditional — all inline:

After a value you can add a colon and a format spec : {' '} . This is where f-strings go from convenient to genuinely powerful. Money, percentages, and aligned columns all come from here.

The most common spec by far is :.2f — "show this float with exactly two digits after the decimal point", perfect for currency. The :, spec instantly makes large numbers human-readable.

Use < (left), > (right), or ^ (center) with a width to line text up into columns — the trick behind every console report:

{' '} left-aligns the name in a 12-character field; {' '} right-aligns the price in an 8-character field with 2 decimals. You can even pick the fill character: {" "} centers nothing in a 20-wide field of asterisks.

Put an = right after an expression inside the braces and Python prints both the expression text and its value. It's the fastest way to sprinkle debug prints:

No more typing the variable name twice. Reach for this any time you'd otherwise write print("x", x) .

Because {' '} means "evaluate this", you need a way to print an actual brace. The rule: double it.

Know how to read them, but write f-strings in new code.

These scrambled lines should compute a discounted price and print a clean formatted line. Reorder them so the final output is Final: $42.50 (15% off) .

Why: discount (A) needs both price (B) and rate (D) to exist first. final (C) depends on the discount, and the f-string (E) reads both final and rate . The :.0% spec turns 0.15 into 15% .

7 — the braces evaluate the full expression 3 * 2 + 1 , following normal operator precedence.

50% — the % spec multiplies by 100 and appends a percent sign; .0 means zero decimal places.

{' '} — the outer doubled braces are literal, the inner single pair interpolates n .

Build a single formatted invoice line for a product, then experiment with the format specs.

Lesson complete — you format like a pro now!

You can embed expressions, format money and percentages, align columns, use the = debug trick, and read the older .format() and % styles. f-strings will appear in nearly every Python file you ever write.

🚀 Up next: String Methods — slice, search, clean, and reshape text with Python's built-in string toolkit.

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