Python Lists

In Python, a list is an ordered collection of elements. It's a type of array that can contain heterogeneous data of various types, such as numerical and alphanumeric values.

list = [element1, element2, element3, ... ]

What's the difference between lists and variables?

Both lists and variables have a name, but a variable can hold only one piece of data. In contrast, a list can store multiple pieces of data.

How to create a list in Python

You assign a name to the list just like you would with a variable.

After the equals sign, you write the ordered collection of data within square brackets, separated by commas.

year = [2010, 2011, 2012]

In Python, square brackets [ ] distinguish lists from other types of arrays such as tuples, sets, and dictionaries.

A list can contain heterogeneous data of different types.

For example, the following list includes both numerical and alphanumeric values.

[2010, 2011, 2012, 2013, 'leap year']

A list can also contain other nested lists and even libraries.

[2010, 2011, 2012, 2013, ['leap year', 'non-leap year']]

How to display a list

To display the elements of a list, use the list's name in the PRINT statement.

print(year)

The result on the screen will be:

[2010, 2011, 2012]

To display a single element from the list, you need to specify the position of the element within square brackets.

print(year[2])

In this case, the interpreter will display only the content of that specific element.

2012

The first element of the list is at position zero [0].

How to find out the number of elements in a list

To find out the number of elements in a list, use the len function.

len(listname)

The len function returns a positive integer that indicates the size of the list, i.e., the number of elements it contains.

A practical example

Given the following list:

year = [2010, 2011, 2012]

To get the size of the list, you write:

print(len(year))

The command returns the number of elements in the list, which is three (3).

3

In this case, I printed the result on the screen.

However, you could use this information for many other useful purposes.

For example, as the upper limit of a loop.

i = 0
while i < len(year):
print(year[i])
i = i + 1

How to modify list elements

To modify a list, you assign new values to its elements.

Example

Given the following list:

year = [2010, 2011, 2012, 2013]

To change the first element, you type:

year[0] = 2009

Now the list is:

[2009, 2011, 2012, 2013]

To modify a group of elements, you use slicing.

Instead of a single index, you specify the start and end positions of the elements.

year[0:2] = [2008, 2009]

After the modification, the list becomes:

[2008, 2009, 2012, 2013]

And so on.