Welcome to Python list comprehension! List comprehension is a powerful and concise way to create lists in Python. Instead of writing traditional for loops with append statements, we can create lists in a single, readable line. Let's see how the traditional approach compares to list comprehension for creating a list of squares.
Now let's explore the basic syntax of list comprehension. The general form is: expression for item in iterable, enclosed in square brackets. The expression defines what value to include for each item, the item is a variable representing each element, and the iterable is any sequence we can loop through. Here are examples using different types of iterables: lists, strings, and ranges.
List comprehensions become even more powerful when we add filtering conditions. By adding an 'if' clause at the end, we can filter items based on specific criteria. Only items that meet the condition will be included in the new list. Let's see examples of filtering even numbers, positive values, and strings by length.
List comprehensions also support conditional expressions using if-else statements. Unlike filtering conditions, conditional expressions go BEFORE the for loop and always produce a list of the same length as the input. They transform values based on conditions rather than excluding items. Here are examples showing how to classify numbers as even or odd, calculate absolute values, and assign letter grades based on scores.
To summarize what we've learned about Python list comprehensions: They provide a concise and readable way to create lists. The basic syntax is expression for item in iterable. You can add filtering conditions with if clauses, use conditional expressions for transforming values, and they're generally more efficient than traditional loops. List comprehensions are a powerful tool that makes Python code more elegant and Pythonic.