python python lists

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Lists

A list in python is a collection of various elements. A list can be a collection of integers, characters, dictionaries, or all of the above, not to be confused with an array. An array requires all elements to be of the same type.

# Empty List empty_list = [] # List of integers number_list = [1, 2, 3, 4, 5] # List of strings alpha_list = ["alpha", "beta", "charlie", "delta", "echo"] # List of dictionaries dict_list = [{"id": 1, "role": "admin"}, {"id": 2, "role": "manager"}] # List of mixed value types mixed_list = [1, "two", 3, False] # check the type type(number_list) # OUTPUT: <class 'list'>

# Access list items by a positive index alpha_list[1] # OUTPUT: 'beta' # Negative index can also be used to access list elements number_list[-2] # OUTPUT: 4 # Length of the list len(alpha_list) # OUTPUT: 5

Slicing

Using indexes, access a subset of a list by using two indexes seperated by a colon [x:y], x element is inclusive, y element is not. Omitting the first index, the slice starts at index 0. Omitting the second index, the slice continues until the end of the string.

number_list[1:3] # OUTPUT: [2, 3] number_list[:4] # OUTPUT: [1, 2, 3, 4] number_list[2:] # OUTPUT: [3, 4, 5] # Negative indexes with slicing can also be used number_list[-3:] # OUTPUT: [3, 4, 5] number_list[:-3] # OUTPUT: [1, 2]

Join & Split

String variables can be split into a list. Default delimiter is a space but a character delimeter can be specified.

"Hello world".split() # OUTPUT: ['Hello', 'world'] "Hello world".split('o') # OUTPUT: ['Hell', ' w', 'rld'] # The Join method does the opposite and combines a list into a string " ".join(['Hello', 'world']) # OUTPUT: 'Hello world' "-".join(['Hello', 'world']) # OUTPUT: 'Hello-world'

Mutable

Lists are mutable.

# Add elements by appending to the end of the list alpha_list = ["alpha", "beta"] alpha_list.append("charlie") alpha_list # OUTPUT: ['alpha', 'beta', 'charlie'] #Insert elements at a specific index alpha_list.insert(0, "delta") alpha_list #OUTPUT; ['delta', 'alpha', 'beta', 'charlie']

Remove/ Delete

Elements can also be removed/deleted from the list.

# del will remove the element at a specific index del alpha_list[3] alpha_list #OUTPUT; ['delta', 'alpha', 'beta'] # Remove will remove the first match in the list # If multiple matches exist in the list, not all elements are removed alpha_list.remove('alpha') alpha_list #OUTPUT; ['delta', 'beta']

For Loop

# Create a List of grades grades = [90, 80, 95, 100, 75] # Iterate over the list and print each individual grade for i in grades: print(i) # OUTPUT: # 90 # 80 # 95 # 100 # 75 # Show indexes for elements in list using the enumerate function in a for loop alpha_list = ["alpha", "beta", "charlie"] for index, alpha in enumerate(alpha_list): print(f"The word at index: {index} is {alpha} ") # OUTPUT: # The word at index: 0 is alpha # The word at index: 1 is beta # The word at index: 2 is charlie

Part 2 of this series will include the more functional programming concepts such as map() and list comprehension examples.

Python Lists, Part 1

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Lists

Index & Length

Slicing

Join & Split

Mutable

Remove/ Delete

Other Helper Methods

For Loop

Command Palette

Comments

More from this blog

Lists

Index & Length

Slicing

Join & Split

Mutable

Remove/ Delete

Other Helper Methods

For Loop