“I need to limit users to 100 requests per minute. I’ll just stick a counter in a dictionary and reset it when the minute changes.” If you’ve ever protected an API endpoint, that thought has probably crossed your mind. On a whiteboard, rate limiting looks like five lines of …

“Why would you need a dedicated caching library? A cache is just a dictionary.” It is very easy to think that way about what, on the surface, looks like a subclass of a dictionary. When you notice a slow database query or a CPU-intensive calculation, reaching for an in-memory dictionary …

“Please enter a valid email address.” “Please provide a valid website URL.” If you build web applications, APIs, or user interfaces, you have almost certainly written or reviewed code that displays those two demands. Because every user recognises an email address and …

When you build an application that displays a collection of items, synchronisation feels deceptively straightforward at first. Your client fetches the current list from an API, your user makes a few edits or removes a row, and you send the updated collection back to the server. If you only test …

Every software engineer has, at some point, written a CSV parser in a single line of code. When you receive a comma-separated file, calling line.strip().split(",") feels delightfully clean and efficient. You run a quick test on three rows of mock data, confirm the output matches your …

At first glance, numbers appear to be the simplest data type in computer science. Unlike natural languages with irregular grammar and complex idioms, numbers feel purely mathematical, universal, and unambiguous. You collect a string of digits from an input field, pass it to your language’s …

When building an application, you inevitably reach a screen where money enters the picture. You need to calculate a 20% VAT rate, split an invoice between team members, or apply a discount code at checkout. You see a price like £19.99 with two neat decimal digits and assume a standard …

At some point in every developer’s career, a tempting thought arrives. You need to add seven days to an appointment, schedule a task for tomorrow morning, or calculate the duration between two events. You glance at your standard library, see a hefty date module, and think: “A day is …