Functions

Learning outcomes

• What functions are and how to define them
• What is a DRY principle?
• How to invoke functions?
• How to return values?
• How to specify function parameters?
• What are default parameters?
• What is a variable scope in Python?

Learning material

Watch these two videos on functions:

• Python Functions
• Scope

Knowledge check

• What is the def keyword used for?
• What keyword lets you give back the result of a function?
• How to specify default parameters?
• How to deal with the unknown number of function parameters?
• What is the LEGB rule?
• What two keywords help you change the score of a variable?

Exercises

1. Define a function that prints a string that you pass in it as a parameter, and call it 5 times using a loop.
2. Create a function calculator that takes three arguments: 2 numbers and a string. The string's value can be one of the 4 values: add, substract, multiply, or divide. Return a result of an operation that corresponds to the string. (Use Python's switch statement, about which you can read more here). Don't forget to put a default case that displays a meaningful message.
3. Make a function that prints out some message. Define the second function that takes a function as a parameter. Call the second function and pass first function as a parameter.
4. Solve a Fibonacci Number problem. Here's the problem formulation on LeetCode.

Additional Resources

• Python Language Reference
• PEP 257 - docstring conventions