UnboundLocalError (“local variable referenced before assignment”) means a function reads a variable that Python has decided is local, before that local variable has been given a value. It almost always happens because the function assigns to a name that also exists outside it. Newer versions of Python, including the Python 3.12.5 I used for every … Read more >>
Scope decides where a Python variable can be seen: a name created inside a function is local, and a name at the top of a file is global. Python looks names up in Local, Enclosing, Global, then Built-in scope, the LEGB rule. These examples ran on Python 3.12.5, and the screenshots come straight from the … Read more >>
Recursion in Python is when a function calls itself to solve a smaller version of the same problem. Every recursive function needs a base case that stops the calls and a recursive case that moves toward it; without a base case Python stops with RecursionError after about 1,000 calls. This guide shows how Python recursion … Read more >>
Regular expressions in Python are patterns for finding, checking, extracting and replacing text, and they are provided by the built-in re module. re.search(r”\d+”, text) finds the first number in a string, re.findall() returns every match, and re.sub() replaces them. This guide covers every re function, the pattern syntax, groups, greedy and lazy matching, flags, lookarounds, … Read more >>
When I build a small reporting script, I often receive an unfamiliar object from a library, API response, or custom class. I need to know what that object contains before I can use it safely. Rather than guessing method names or digging through code first, I use the Python dir() function. The dir() function gives … Read more >>
When I build a small reporting script, I often need a fast way to organize related details. For example, an employee record may need a name, department, email, and monthly sales figure. Keeping those values in separate variables becomes messy quickly. That is where the Python dict() function helps. It creates a dictionary, which stores … Read more >>
When I build small automation scripts, I often create objects to hold temporary report data—such as a customer’s draft notes, an API token, or a calculated status. Once that information is no longer valid, I do not want it sitting on the object and getting reused accidentally. That is where the Python delattr() function helps. … Read more >>
A few years ago, I worked on a small signal-analysis script for a Chicago engineering team. The input data included values such as 12+5j, and the script needed to calculate magnitudes, phase angles, and combined signals. Regular integers and floats were not enough. That is where Python’s built-in complex() function becomes useful. It creates complex … Read more >>
To initialize an array in TypeScript, declare the element type and give it a value: const cities: string[] = [“Austin”, “Denver”], or const ids: string[] = [] to start empty. Array<string> means the same as string[]. For a fixed number of slots use Array.from({ length: n }, …) rather than new Array(n), which leaves holes. … Read more >>
To check if an array is null or empty in TypeScript, write if (!items || items.length === 0), or the shorter if (!items?.length), which covers null, undefined and [] in one test. The order matters: reading .length before the null check throws at runtime. This guide shows both forms running against all four cases, the … Read more >>
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