The FiftyPage blog

Short answers to real coding questions. One topic, one working example, no fluff, the same way our books teach.

• DevOps & CloudKubernetes Deployment YAML explainedRead a Kubernetes Deployment YAML line by line, then change the replica count and quickly scale your app up with kubectl apply.November 2, 2026 · 2 min read
• Machine LearningCross-validation in scikit-learn explainedLearn how sklearn cross_val_score runs 5-fold cross-validation and why a single train/test split can give a misleading score.November 2, 2026 · 2 min read
• Data Sciencepandas groupby explained with examplesLearn how pandas groupby totals sales per product and how agg builds a summary table with several statistics, with a runnable example.November 2, 2026 · 1 min read
• Backend & APIsHow to build your first REST API with FastifyBuild a GET /products route in Fastify that returns JSON, then run it with an npm script and test it with curl. Beginner friendly.November 2, 2026 · 2 min read
• Databases & SQLSQL JOIN vs LEFT JOIN with examplesLearn the difference between SQL JOIN and LEFT JOIN with a customers and orders example, and see exactly which rows each one keeps.November 1, 2026 · 2 min read
• Web DevelopmentReact useEffect: dependencies, fetching and cleanupLearn how useEffect runs, how its dependency array works, and how to fetch products and cancel a stale request in the cleanup function.November 1, 2026 · 2 min read
• AI & LLMsLLM Structured Output with Pydantic in PythonTurn an LLM reply into a validated Python object: define a Pydantic model, extract order details from an email, and catch bad JSON early.November 1, 2026 · 2 min read
• JavaScript & TypeScriptJavaScript closures explained simplyLearn what a JavaScript closure is by building a counter factory whose inner function remembers its variable, plus the classic var loop mistake.October 31, 2026 · 2 min read
• PythonHow to count items with a Python dictionaryLearn how to count occurrences in Python with a dictionary, dict.get and a loop, by building a small word-frequency counter step by step.October 31, 2026 · 1 min read
• AI at WorkHow to write a good AI prompt: the five-part recipeLearn the five-part recipe for AI prompts: goal, context, example, format and tone, shown by rewriting a vague email request into a clear one.October 31, 2026 · 2 min read
• Career & InterviewsBig-O notation explained in plain wordsLearn what O(1), O(n) and O(n²) mean by timing three small Python functions and watching how each one grows when the input doubles.October 31, 2026 · 2 min read
• C# & .NETC# LINQ basics: Where, Select and OrderByLearn how to filter, sort and reshape a list in C# with LINQ's Where, Select and OrderBy, using a small coffee menu you can run.October 30, 2026 · 2 min read
• Java & KotlinJava ArrayList explained with examplesLearn how to add, remove, loop over and sort a Java ArrayList, using a small list of prices, plus the remove() mistake that trips up beginners.October 30, 2026 · 2 min read
• Go, Rust & C++Go slices and maps explained with examplesLearn how to append to a Go slice, loop with range and count words with a map, using one small runnable example and its real output.October 30, 2026 · 2 min read
• MobileSwiftUI @State and @Binding explainedLearn how @State owns a value and @Binding lets a child view change it, by building a quantity stepper you can run in Xcode.October 29, 2026 · 2 min read
• Git & ToolsGit rebase vs merge: what's the difference?Merge or rebase? See the same feature branch integrated both ways, compare the resulting history, and learn the golden rule of rebasing.October 29, 2026 · 2 min read
• DevOps & CloudHow to write a Dockerfile for a Python appWrite a Dockerfile for a small Flask app, then build and run it with Docker. Learn what each line does and avoid the two most common mistakes.October 29, 2026 · 2 min read
• Machine Learningscikit-learn train_test_split and your first modelLearn how to split data with train_test_split, fit a KNeighborsClassifier, score it on test data and compare it with a baseline.October 29, 2026 · 2 min read
• Data ScienceHow to read a CSV file with pandasLearn how to load a CSV into a pandas DataFrame with read_csv, then check it with head, shape and info and load only some columns with usecols.October 28, 2026 · 1 min read
• Backend & APIsNode.js environment variables and .env filesRead process.env with defaults, convert strings to numbers and booleans, and load a .env file with node --env-file without committing secrets.October 28, 2026 · 1 min read
• Databases & SQLSQL GROUP BY and HAVING explained with examplesLearn how SQL GROUP BY totals rows per group with SUM and COUNT, and how HAVING filters those groups, with a runnable example and output.October 28, 2026 · 2 min read
• Web DevelopmentReact useState Explained for BeginnersLearn how React useState works by building a quantity counter, and see why a plain variable never updates the screen in React.October 27, 2026 · 2 min read
• AI & LLMsHow to Call the Claude API from Python with StreamingSend your first Claude API message from Python, read the stop reason and token usage, then stream the reply text as it is written.October 27, 2026 · 2 min read
• JavaScript & TypeScriptJavaScript map and filter explained with examplesLearn how JavaScript map and filter work on arrays of objects, with a runnable example that filters products by price and chains map.October 27, 2026 · 2 min read