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Truthiness

Learn values considered true/false.

Truthiness

Python evaluates every value as bool. Falsy values: 0, 0.0, , [], None. Others are truthy.

name = "Alex"
if name:  # truthy
    print("Has a name")

This gives a very short way to say "if not empty". if text: is True when text is non-empty.

Checking the opposite with not

not flips the truthiness of a value. not name is True when name is empty.

name = ""
if not name:
    print("No name")

This is a short way to say "if empty". With if not text: you can check for an empty string, empty list or None.

Practice Print with truthiness

Assign name = "Alex". Write if name: print("Has a name").

Starter code

main.py
# Use truthiness

Sample solution

main.py
name = "Alex"
if name:
    print("Has a name")

Expected output

Has a name

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which is falsy?

  • "text"
  • 0 Correct answer
  • 1
  • [1, 2]

Explanation: 0 is a falsy value.

2 Empty string check

Question 
name = "Alex"
if ____:
    print("Has a name")
Answer 
name = "Alex"
if name:
    print("Has a name")

Explanation: if name is True for a non-empty string (truthy).

3 Match the values

Term Meaning
0 Zero (falsy)
"text" String (truthy)
[] Empty list
None None value

All lessons in Beginner

1 Python basics

  1. What is Python?
  2. REPL and print
  3. Comments
  4. Indentation blocks
  5. python -c and scripts
  6. Summary - Python basics

2 Variables

  1. Variable assignment
  2. Multiple assignment
  3. Naming variables
  4. id and type
  5. Swapping variables
  6. Summary - Variables

3 Data types

  1. int and float
  2. bool
  3. str basics
  4. None
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Membership and identity
  6. Summary - Operators

6 String basics

  1. f-string
  2. Concatenation
  3. str.format
  4. Raw strings
  5. Triple-quote
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. elif and else
  3. Nested if
  4. Truthiness
  5. Conditional expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. range
  3. The while loop
  4. break and continue
  5. Loop else
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Lists

  1. Declaring lists
  2. Index and slice
  3. List methods
  4. in and count
  5. Sorting lists
  6. Summary - Lists

11 List comprehension

  1. Comprehension basics
  2. Filtered comprehension
  3. Dict and set comprehension
  4. Nested comprehension
  5. Generator expression
  6. Summary - List comprehension

12 Tuple, set and dict

  1. Tuple
  2. Set
  3. Dict basics
  4. Dict methods
  5. Dict comprehension
  6. Summary - Tuple, set and dict

13 Functions

  1. def
  2. return
  3. Docstring
  4. Default parameters
  5. *args and **kwargs
  6. Summary - Functions

14 Function parameters

  1. Positional parameters
  2. Keyword parameters
  3. Keyword-only
  4. Positional-only
  5. Type hints basics
  6. Summary - Function parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string methods

  1. split and join
  2. strip, lstrip, rstrip
  3. replace
  4. find and index
  5. startswith, endswith
  6. Summary - Advanced strings

17 Input and output

  1. input()
  2. int/float conversion
  3. print parameters
  4. f-string formatting
  5. sys.argv
  6. Summary - Input and output

18 Error handling

  1. try/except
  2. else and finally
  3. raise
  4. Exception hierarchy
  5. Custom exceptions
  6. Summary - Error handling

19 Modules

  1. import
  2. from import
  3. as alias
  4. __name__ == '__main__'
  5. Standard library
  6. Summary - Modules

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together