![]() ![]() Remember to increase the index by 1 after each iteration. Use the len () function to determine the length of the list, then start at 0 and loop your way through the list items by referring to their indexes. The defaultdict class from the collections module can be used to create a dictionary with default values, but it requires a sort of factory function: it needs a callable passed into it that will create those default values. You can loop through the list items by using a while loop. Example: Based on a list of fruits, you want a new list, containing only the fruits with the letter 'a' in the name. The list function is also a handy way to make a "factory function" that creates a new empty list. List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list. ![]() mylist for i in range(50): mylist. ![]() symbol to represent multiplication, but when the operand on the left. That's by far the most handy reason to use list and I very often see folks forget that list is a great tool for exactly this purpose! In python, as far as I know, there are at least 3 to 4 ways to create and initialize lists of a given size: Simple loop with append. Lists can be created using the repetition operator. Those first three reasons to use list are all about taking an old iterable and making a new list out of it. It is a very concise way to create a new list by. for number in numbers: if number in unique: continue else: unique. You use lists in Python to store information. A list is a series of values that contain variables of any type. I use a for loop to iterate through each number in the numbers list. As a developer, youll work with many lists. Eventually, this list will hold all of the unique numbers. Inside the function, I create an empty list, unique. This use case for list is really just a variation of the last two, but this is an important enough concept that it's worth repeating in 3 different ways! Using list as a factory function List comprehension in Python is an easy and compact syntax for creating a list from a string or another list. I pass this list into my function, getuniquenumbers. In fact, many new Pythonistas might assume that readlines would return an iterator ( many built-in functions return iterators after all). With my_file.readlines(), it's not quite as obvious that we're creating a list of lines. With list(my_file), it's clear that we're looping over a file and storing each line in a new list (assuming you know that looping over a file provides lines). ![]()
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