Is the Truthiness & None lesson free?

Yes. The first 5 lessons on PyRun are free forever — no signup, no card. Truthiness & None runs real Python in your browser via Pyodide.

How long does the Truthiness & None lesson take?

About 5 minutes end-to-end. It's a hands-on lesson — you read a paragraph, edit the code, and run it in the same tab.

Do I need to install Python to try the Truthiness & None lesson?

No install required. PyRun runs real CPython in your browser via Pyodide (Python compiled to WebAssembly). Works on Chrome, Firefox, Safari, and Edge — desktop or mobile.

What level is the Truthiness & None lesson?

Beginner level. No prior Python required — good starting point.

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Beginner·5 min·basics · truthiness

Truthiness & None

You’ll be able to

Recognize what Python treats as truthy vs falsy
Use is vs == correctly, especially with None
Handle empty containers, zero, and empty strings idiomatically
Write concise conditionals using truthiness shortcuts

Why this matters

Python's falsy rules (0, '', [], {}, None all falsy) power idioms like if not users: and trip up devs from Java or C. None versus falsy is the source of countless bugs in Django form handling and API validation.

Common pitfalls

Using if x == None. PEP 8 mandates if x is None; == can be overridden and give false positives.
Treating 0 as missing data. if not count: triggers on both None and 0; use if count is None when zero is valid.
Assuming empty containers raise. bool([]) is False, so if my_list: cleanly guards against empty lists.

Python lets you ask if value: directly. The rule:

What's "falsy"

False, None
0, 0.0
"", [], {}, set() — empty containers

Everything else is "truthy".

`is` vs `==`

== checks equality of values
is checks identity (same object in memory)
Always use is for None: if x is None:

Try it

Write a function that returns the first truthy item from a list, or None.
What does bool("False") return? Why?

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
Given data = [], print "empty" if the list is empty, otherwise print "has items". Use the Pythonic truthiness check (no len(data) == 0).
Exercise 2
Given x = None, print "missing" if x is None, otherwise print its value. Use the correct is check, not ==.
Exercise 3
Write a function first_truthy(items) that returns the first truthy value from a list, or None if there isn't one. Then print first_truthy([0, "", None, "hello", 5]) — expected: hello.

← PreviousDictionaries Next →enumerate, zip, range

Truthiness & None

You’ll be able to

Recognize what Python treats as truthy vs falsy
Use is vs == correctly, especially with None
Handle empty containers, zero, and empty strings idiomatically
Write concise conditionals using truthiness shortcuts

Why this matters

Common pitfalls

Using if x == None. PEP 8 mandates if x is None; == can be overridden and give false positives.
Treating 0 as missing data. if not count: triggers on both None and 0; use if count is None when zero is valid.
Assuming empty containers raise. bool([]) is False, so if my_list: cleanly guards against empty lists.

Python lets you ask if value: directly. The rule:

What's "falsy"

False, None
0, 0.0
"", [], {}, set() — empty containers

Everything else is "truthy".

`is` vs `==`

== checks equality of values
is checks identity (same object in memory)
Always use is for None: if x is None:

Try it

Write a function that returns the first truthy item from a list, or None.
What does bool("False") return? Why?

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
Given data = [], print "empty" if the list is empty, otherwise print "has items". Use the Pythonic truthiness check (no len(data) == 0).
Exercise 2
Given x = None, print "missing" if x is None, otherwise print its value. Use the correct is check, not ==.
Exercise 3
Write a function first_truthy(items) that returns the first truthy value from a list, or None if there isn't one. Then print first_truthy([0, "", None, "hello", 5]) — expected: hello.

Truthiness & None

What's "falsy"

is vs ==

Try it

Truthiness & None

What's "falsy"

is vs ==

Try it

`is` vs `==`

`is` vs `==`