Phase 1: Programming Fundamentals I · ~35 minutes · Python · uv

Control Flow — Conditionals

Python physically will not let you write if x = 5: — and that refusal is a safety feature, not an inconvenience.

Hiring signal: Distinguishes = from == on sight and correctly reasons about truthy/falsy edge cases instead of guessing

What you will learn

Write if/elif/else chains that branch correctly, including boundary values
Explain the difference between = (assignment) and == (comparison), and why confusing them is a real error class
List Python's falsy values and explain why they're falsy
Predict whether a truthy/falsy edge case executes a given branch

Introduction

Type: Learn Languages: Python Prerequisites: Lesson 01 (Variables, Types, and the Assignment Trap) Time: ~35 minutes

Objective

Learning objectives

Write if/elif/else chains that branch correctly, including at boundary values
Explain the difference between = (assignment) and == (comparison), and why confusing them is a real, common error class
List Python's falsy values and explain why they're falsy
Predict whether a truthy/falsy edge case executes a given branch

What you're building

A script (grade_calculator.py) that:

Defines a grade_band(score) function using the boundaries above (90/80/70/60), using >= correctly at every boundary
Tests it against at least six values, including at least two exact boundary values (like 90 and 80) and one just-below-boundary value (like 89.999)
A short written note (as a comment or a printed line) diagnosing what would happen if >= were replaced with > at the 90 boundary specifically

A student writes if []: inside their program and is confused that the branch never runs, "even though [] is a real, valid list, not nothing." What's the accurate explanation?

"Falsy" is not the same claim as "invalid" or "doesn't exist." [] is a completely real, valid Python list — you can call methods on it, pass it to functions, check its type. It is simply also one of the specific values Python treats as False when used directly as a condition, exactly like 0 is a real, valid number that's also falsy. This is consistent everywhere a value is used as a condition — if, while, and boolean operators like and/or all use the same truthy/falsy rules, not a special case for if alone.

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