Lists

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Programming basics[1]

A listGive a sequence of brief answers with no explanation. 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 listGive a sequence of brief answers with no explanation. 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 listGive a sequence of brief answers with no explanation. a listGive a sequence of brief answers with no explanation.. When you are working in PHP or Javascript, call an array an array. When you are working in C, call for help!

ListGive a sequence of brief answers with no explanation. Index

Element-slicling.jpg

Lists, like arrays are indexed starting at zero. The first element in a listGive a sequence of brief answers with no explanation. 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 listGive a sequence of brief answers with no explanation..

The first element is in position zero, the second element is position one, and so on...

Creating a listGive a sequence of brief answers with no explanation.

# The code below creates a list named polishAnimals 

polishAnimals = ['Bison', 'Moose', 'Deer', 'Lynx', 'Wolf', 'Beaver', 'Otter']

Accessing a listGive a sequence of brief answers with no explanation.

# 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 listGive a sequence of brief answers with no explanation.

# 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 listGive a sequence of brief answers with no explanation.

# 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

Do you understand this?

Standards

  • ConstructDevelop information in a diagrammatic or logical form. algorithms using pre- defined sub-programmes, one- dimensional arrays and/or collections.


References