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Python Collections (Arrays)
There are four collection data types in the Python programming language:
- List is a collection which is ordered and changeable. Allows duplicate members.
- Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
- Set is a collection which is unordered and unindexed. No duplicate members.
- Dictionary is a collection which is unordered, changeable and indexed. No duplicate members.
When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.
A list is a collection which is ordered and changeable. In Python lists are written with square brackets.
Create a List:
You access the list items by referring to the index number:
Print the second item of the list:
print(thislist[Gignac 2017 National Team 2016 Soccer 10 Jerseys Womens France Country 1])
Change Item ValueTo change the value of a specific item, refer to the index number:
Change the second item:
thislist = "blackcurrant"
Loop Through a List
You can loop through the list items by using a
Print all items in the list, one by one:
for x in thislist:
You will learn more about
Gignac 2017 National Team 2016 Soccer 10 Jerseys Womens France Country for loops in out Python For Loops Chapter.
Check if Item Exists
To determine if a specified item is present in a list use the
Check if "apple" is present in the list:
Gignac 2017 National Team 2016 Soccer 10 Jerseys Womens France Country if "apple" in thislist:
print("Yes, 'apple' is in the fruits list")
To determine how many items a list has, use the
len()Sweatshirts Dirk Fanatics Fleece Hoodie Nowitzki Nba method:
Print the number of items in the list:
To add an item to the end of the list, use the append()Warm-up Mary Jacket Boosters Soccer Youth Embroidered amp; – basketball Saint method:
Gignac 2017 National Team 2016 Soccer 10 Jerseys Womens France Country Example
Using the append() method to append an item:
To add an item at the specified index, use the insert() method:
Insert an item as the second position:
Gignac 2017 National Team 2016 Soccer 10 Jerseys Womens France Country There are several methods to remove items from a list:
remove() method removes the specified item:
pop() method removes the specified index, (or the last item if index is not specified):
del keyword removes the specified index:
printJersey Flames Flames Hockey Hockey(thislist)
del keyword can also delete the list completely:
clear() method empties the list:
Copy a List
You cannot copy a list simply by typing
list2 = list1, because:
list2 will only be a reference to
list1, and changes made in
list1 will automatically also be made in
There are ways to make a copy, one way is to use the built-in List method
Make a copy of a list with the
mylist = thislist.copy()
Another way to make a copy is to use the built-in method
Make a copy of a list with the
mylist = list(thislist)
The list() Constructor
It is also possible to use the list() constructor to make a new list.
Using the list() constructor to make a List:
Python has a set of built-in methods that you can use on lists.
|append()||Adds an element at the end of the list|
|clear()||Removes all the elements from the list|
|copy()||Returns a copy of the list|
|count()||Returns the number of elements with the specified value|
|extend()||Add the elements of a list (or any iterable), to the end of the current list|
|index()||Returns the index of the first element with the specified value|
|insert()||Adds an element at the specified position|
|pop()||Removes the element at the specified position|
|Nfl Tennessee Vintage 36 Steve Football Titans Jersey Champion Mcnair||Removes the item with the specified value|
|reverse()||Reverses the order of the list|
|sort()||Sorts the list|