Lesson 06 of 55
9 mins readPython Booleans, Nil & Truth Values
In Plain English
In Lua, **only `false` and `nil` evaluate to false**. Crucially, the number `0` and the empty string `""` are truthy in Lua! Logic operators are `and`, `or`, and `not`.
Deep Dive: How It Works
The Only Two Falsy Values: `false` and `nil`. Everything else (including `0` and `""`) is TRUE.
Short-Circuit `and`: Returns its first argument if false/nil; otherwise returns its second argument.
Short-Circuit `or`: Returns its first argument if truthy; otherwise returns its second argument.
Ternary Idiom: `condition and val_if_true or val_if_false` (requires val_if_true to not be false/nil).
Core Rules to Remember
0 and "" are TRUTHY: Major difference from C/JS/Python: 0 is completely true in Lua boolean conditions.
Default Value Idiom: `x = x or "default"` is standard Lua idiom for defaults.
Live Interactive Example
Hit Run Code to see it liveLua Truth Values and Idioms
Python 3.12
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Output Console
Click "Run Code" to view the rendered output.
How it works: 0 and "" both evaluated to true. or provided default 8080.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Implement Default Fallback with or
- Declare `local user_name = nil`.
- Set `local display_name = user_name or "Guest"`.
- Print `"Welcome: " .. display_name`.
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Sandbox Output
Click "Run & Check" to test your solution.
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