Lists: Difference between revisions
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Lists, like arrays are indexed starting at zero. The first element in a list is the "zero-th" element. In the example above (thank you for permission to use this image, programiz.com) <ref>https://www.programiz.com/python-programming/list</ref> we can see also negative numbers, which are helpful if you want to select (or slice) a range of elements from a list. | Lists, like arrays, are indexed starting at zero. The first element in a list is the "zero-th" element. In the example above (thank you for permission to use this image, programiz.com) <ref>https://www.programiz.com/python-programming/list</ref> we can see also negative numbers, which are helpful if you want to select (or slice) a range of elements from a list. | ||
The first element is in position zero, the second element is position one, and so on... | The first element is in position zero, the second element is position one, and so on... | ||
Revision as of 11:37, 20 June 2019
A list is a data structure in Python that is a mutable, or changeable, ordered sequence of elements. Each element or value that is inside of a list is called an item. Just as strings are defined as characters between quotes, lists are defined by having values between square brackets [ ].[2]
Please be careful as lists can be thought of as analogous to arrays, but they aren't the same thing. Arrays traditionally have a fixed memory size whilst lists have dynamic memory allocation. When you are working in Python, call a list a list. When you are working in PHP or Javascript, call an array an array. When you are working in C, call for help!
List Index[edit]
Lists, like arrays, are indexed starting at zero. The first element in a list is the "zero-th" element. In the example above (thank you for permission to use this image, programiz.com) [3] we can see also negative numbers, which are helpful if you want to select (or slice) a range of elements from a list.
The first element is in position zero, the second element is position one, and so on...
Creating a list[edit]
# The code below creates a list named polishAnimals
polishAnimals = ['Bison', 'Moose', 'Deer', 'Lynx', 'Wolf', 'Beaver', 'Otter']
Accessing a list[edit]
# If you want to print a list (kind of ugly) you can simply:
print(polishAnimals)
# However, it is far more common to slice into a list
# The code below accesses the 2nd item in the list named 'polishAnimals'
print(polishAnimals[2])
# there is a lot more to slicing in Python.
Inserting into a list[edit]
# if we want to add onto a list (append) we could simply use the append method. The code below appends wild board onto the end of our list.
polishAnimals.append('wild boar')
# if we wanted to replace a certain element, we could simply overwrite it. Below we are replacing the 2nd item of our list with a new animal:
polishAnimals[1] = 'Stork'
Deleting an element from a list[edit]
# There are a few different ways to remove an element from a list. The first way is to call the remove method.
# The remove method works by finding the name of an element.
polishAnimals.remove('Moose')
# another way to remove an element from a list is to call the pop method. Pop-ing removes an index and return the value you removed.
# the line below removes the 2nd element from our list and makes it available for us to use.
polishAnimals.pop(1)
# we might use the pop method like this:
animalsDeleted = polishAnimals.pop[1]
# we can also use the del function.
del polishAnimals[2]
# to delete an entire list, call the clear method (this is only available in Python 3+
polishAnimals.clear
Standards[edit]
- Construct algorithms using pre- defined sub-programmes, one- dimensional arrays and/or collections.