Leveling Up: Comprehensions and Lambdas

You now know enough Python to build real programs. This lesson levels you up with two tools that make code shorter and more "Pythonic": comprehensions and lambda functions. They are common in professional code, so recognizing them matters.

What You'll Learn

• List comprehensions to build and filter lists
• Dict and set comprehensions
• Lambda functions for quick one-line logic
• Using lambdas with sorted, map, and filter

List Comprehensions

A comprehension builds a list in one line. Compare the loop to the comprehension:

The pattern is [expression for item in iterable].

Filtering With if

Add an if at the end to keep only items that match:

Dict and Set Comprehensions

The same idea builds dictionaries and sets:

Lambda Functions

A lambda is a tiny anonymous function written in one line: lambda args: expression. It is handy when you need a quick function to pass to another function:

Lambdas With sorted, map, and filter

This is where lambdas earn their keep. Give sorted a key to sort by something custom, or transform and filter whole lists:

When to Use Which

• Reach for a comprehension to build or filter a collection
• Reach for a lambda for a short throwaway function passed to sorted, map, or filter
• For anything longer or reused, write a normal def function

Key Takeaways

• List comprehension: [expr for item in iterable]
• Filter by adding if condition at the end
• Dict and set comprehensions use { }
• lambda args: expression is a one-line function
• Lambdas pair naturally with sorted, map, and filter