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We make lists all the time: shopping lists, TODO lists, wish lists. Thus, it’s
natural that Python would provide a list
class for just that purpose. Lists
can contain any Python objects that you choose as a comma-delimited sequence
surrounded with brackets:
x = 1
l = [2, "cat", x]
print(l)
This will output:
[2, 'cat', 1]
We see here that our list contains a number, a string, and a variable! A very eclectic collection of Python objects if you ask me. :)
Python also supports multiple useful operations when it comes to handling lists, such as:
Adding Elements
You can add elements to a list by using the append
method, which takes a single
Python object to be added to the end of the list:
l = [1, 2, 3]
l.append("anything")
print(l)
This will output:
[1, 2, 3, 'anything']
Removing Elements
You can remove elements from a list by using the remove
method, which takes
any Python object to be removed from the list:
l = [1, 2, 3]
l.remove(2)
print(l)
This will output:
[1, 3]
What happens if we try to remove an element that already does not exist?
l = [1, 2, 3]
l.remove(4)
If we try to do this, Python will raise an error:
...
ValueError: list.remove(x): x not in list
Indexing
If we want to access the nth
element in a list, we write out the list object
(or the variable assigned to that list), followed by brackets containing the
index corresponding to the element that we want:
l = [1, 2, 3]
print(l[1])
This will output:
2
That’s odd! Isn’t Python returning the 2nd
element in the list? That’s because
Python uses zero-indexing, meaning list indices begin at 0
. Thus, the 2nd
element of the list corresponds to an index of 1
. More generally, the nth
element of the list corresponds to an index of n - 1
.
What happens if we try to access an index that does not exist?
l = [1, 2, 3]
print(l[1000])
If we try to do this, Python will raise an error:
...
IndexError: list index out of range
There are a lot of other list
methods that are available beyond the ones
listed, but we’ll stop here for the time being and practice what we have learned:
Create a
list
with the following elements:23
,"dog"
, and5
. (solution)With your newly created list, append the element
"cat"
and remove the element23
from your list. (solution)With your modified list, how would you print the
1st
element? (solution)
If you’re comfortable handling lists, feel free to proceed to Lesson 7!