Python f-strings — 7 Things You Can Do

An f-string is the modern way to build strings in Python. The f prefix turns the string into a template, and anything inside curly braces gets evaluated and dropped in. That much most people know. But f-strings have a much deeper format spec mini-language — number formatting, alignment, percentages, the = debugging shortcut, conversion flags, multi-line templates, and date formatting all live inside the same braces. This tutorial walks seven things you can do with f-strings, on a tiny demo with a name, a price, and a date. Each example is one or two lines. The point is to leave you with a mental shelf of patterns to reach for the next time you build a string in Python. What You'll Build: - f_string_examples.py — one file, seven numbered patterns, runs in under a second. - Pattern 1: basic interpolation — f"Hello, {name}". Drop a variable into a string. - Pattern 2: format spec — f"${price:,.2f}" for thousand-separator + 2 decimals, f"{count:gt6}" for right-padding, f"{pct:.2%}" for percentage. Same colon-and-spec syntax as the old .format method. - Pattern 3: expressions inside the braces — f"{items[0]}", f"{sum(items)}", f"{name.upper()}". Anything that evaluates to a value works. Method calls, indexing, arithmetic. - Pattern 4: = for debugging (Python 3.8+) — f"{x=}" prints x=10. Saves typing the variable name twice when you're sticking print statements into code to figure out what's wrong. - Pattern 5: !r / !s / !a conversion flags — f"{val!r}" calls repr(), !s calls str(), !a calls ascii(). The !r form is the most useful — it quotes strings, so you can tell "5" from 5 in your debug output. - Pattern 6: multi-line f-strings — triple-quote a template, embed values across multiple lines. Useful for printing structured reports. - Pattern 7: date and time formatting — f"{today:%Y-%m-%d}". The format spec accepts strftime codes for dates and datetimes. No more importing strftime separately. Timestamps: 0:00 - Intro — f-strings in one minute 0:22 - Preview — seven patterns coming up 1:07 - Open f_string_examples.py in nvim 1:25 - Pattern 1 — basic interpolation 1:42 - Pattern 2 — format spec for numbers 2:05 - Pattern 3 — expressions in braces 2:25 - Pattern 4 — = for debugging 2:45 - Pattern 5 — conversion flags 3:08 - Pattern 6 — multi-line 3:30 - Pattern 7 — date formatting 3:55 - Save and run 4:10 - Walk through the output 4:30 - End screen — recap Key Takeaways: 1. An f-string is a template — the f prefix turns the string into one. Anything inside curly braces gets evaluated and substituted in at runtime. The expression can be a variable, a method call, an index, arithmetic — anything that produces a value. 2. The format spec mini-language lives after a colon inside the braces. {price:,.2f} is comma-separator, 2 decimals. {count:gt6} is right-pad to width 6. {pct:.2%} is percentage with 2 decimals. Same syntax as the old .format method and the format() built-in. 3. The = debug shortcut (Python 3.8+) is the killer feature for sticking print statements into code. f"{x=}" prints x=10. Saves you from typing the variable name twice as both label and value. Use everywhere you'd reach for print-debugging. 4. Conversion flags — !r, !s, !a — call repr, str, and ascii respectively before formatting. !r is the most useful in practice: it quotes strings in the output, so you can tell empty strings from None and a string '5' from the number 5 in your debug logs. 5. The format spec accepts strftime codes for dates and datetimes. f"{today:%Y-%m-%d}" formats a date without importing strftime separately. Same for percentage, hex, binary, scientific notation — all the format codes from the format-spec mini-language work inside f-string braces. 📺 Deeper dive: Common Questions Ep 12 (List Comprehensions) is a similar "patterns you'll meet in real code" walk-through for another Python idiom. https://www.youtube.com/watch?v=-ZJmrY48290 This channel is run by Claude AI. Tutorials AI-produced; reviewed and published by Codegiz. Source code at codegiz.com. #Python #FStrings #PythonTutorial #LearnPython #PythonFormatting #PythonBasics #PythonTips --- Generated by Claude AI · part of the Common Questions in Python series