Grundlæggende om Booleans
Every decision your program makes - whether to show a message, repeat a step, or validate input - relies on a Boolean: True or False. Learn how Booleans work and how regular Python values behave in conditional expressions.
What Is a Boolean?
A Boolean is a value that represents truth: True or False (note the capitalization). You'll often get Booleans from comparisons - age >= 18 yields True when the condition holds - and you'll use them directly in control flow, e.g. if is_adult:.
Truthiness in Practice
In if/while conditions, Python treats many objects as "truthy" or "falsey". Empty or zero-like values are considered false, everything else is true. This lets you write natural checks such as if items: or if name: without extra comparisons.
Common Falsey Values
False;None;0,0.0;""(empty string);- Empty containers:
[],(),{},set().
Non-empty strings are truthy - even "0" or "False".
12345678910profile_complete = True user_name = "" messages_sent = 0 if profile_complete: print("Welcome to your dashboard!") # Printed because profile is complete print(bool(user_name)) # False → no name provided yet print(bool(messages_sent)) # False → user hasn't sent any messages print(bool("ok")) # True → any non-empty string counts as valid input
1. Which value is falsey in Python?
2. What value will this code output?
3. Which if will not execute its body?
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Every decision your program makes - whether to show a message, repeat a step, or validate input - relies on a Boolean: True or False. Learn how Booleans work and how regular Python values behave in conditional expressions.
What Is a Boolean?
A Boolean is a value that represents truth: True or False (note the capitalization). You'll often get Booleans from comparisons - age >= 18 yields True when the condition holds - and you'll use them directly in control flow, e.g. if is_adult:.
Truthiness in Practice
In if/while conditions, Python treats many objects as "truthy" or "falsey". Empty or zero-like values are considered false, everything else is true. This lets you write natural checks such as if items: or if name: without extra comparisons.
Common Falsey Values
False;None;0,0.0;""(empty string);- Empty containers:
[],(),{},set().
Non-empty strings are truthy - even "0" or "False".
12345678910profile_complete = True user_name = "" messages_sent = 0 if profile_complete: print("Welcome to your dashboard!") # Printed because profile is complete print(bool(user_name)) # False → no name provided yet print(bool(messages_sent)) # False → user hasn't sent any messages print(bool("ok")) # True → any non-empty string counts as valid input
1. Which value is falsey in Python?
2. What value will this code output?
3. Which if will not execute its body?
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