Python - List - Python - DYclassroom

In this tutorial we will learn about list in Python.

We briefly talked about list in the Python - Data Type tutorial.

What is a list?

A list is an ordered sequence of items. We use square brackets [ ] to create a list in Python.

The items of a list are comma , separated and can be of multiple types like integer, floating point number, string, boolean, complex number.

A list can have an item repeated multiple times.

In the following example we are creating a list of integer numbers.

myList = [1, 2, 3]

The `list()` constructor

We use the list() constructor to create a list in Python.

# list
myList = list((1, 3.14, 'yusufshakeel', 1+2j, True))

print("Type of myList:", type(myList))
print(myList)

Output

Type of myList: <class 'list'>
[1, 3.14, 'yusufshakeel', (1+2j), True]

Accessing list items

Items of a list are indexed and the first item of the list gets index 0, the second item of the list gets index 1 and so on.

Index of a list in Python is an integer value like other programming languages - C and Java.

If a list has 10 items then the last item will be at index (n - 1) i.e. 9.

We access list items using list[index] notation.

Where, list represents the list variable and index is the index of the item that we want to access.

In the following example we are printing the items at index 1 and 3 for the given list.

# list
myList = [1, "two", True, 3.14, 2+3j]

print(myList[1])    # "two"
print(myList[3])    # 3.14

Manipulating list items

We manipulate (change) list items using list[index] = value notation.

Where, list denotes a list variable, index is the index of the item that we want to change and value is the new value that we are assigning to the list item at the given index.

In the following Python program we are changing the value at index 3.

# list
myList = [1, "two", True, 3.14, 2+3j]

print("Before", myList)

# change
myList[2] = False

print("After", myList)

We will get the following output.

Before [1, 'two', True, 3.14, (2+3j)]
After [1, 'two', False, 3.14, (2+3j)]

Counting list items

We can find the total number of items present in a given list using the len() method.

In the following Python program we are printing out the total number of items present in the given list.

# list
myList = [1, "two", True, 3.14, 2+3j]

print("Total number of items:", len(myList))

We will get the following output.

Total number of items: 5

Loop through list items

We can use for loop and while loop to loop through items of a given list.

In the following example we are printing all the items of a given list using for loop.

# list
myList = [1, "two", True, 3.14, 2+3j]

for i in myList:
    print(i)

The above Python program will give us the following output.

1
two
True
3.14
(2+3j)

We can also use the while loop to achieve the same result.

# list
myList = [1, "two", True, 3.14, 2+3j]

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

Checking list items

If we want to check whether a given item is present or not present in a list we use the in - membership operator.

If the item we are looking for exists in the list then we will get True, otherwise False.

In the following Python program we are checking if 3 and "Hello" are present in the given list.

# list
myList = ["Food", 2, 3.14, "Hello", False]

# is 3 present
if 3 in myList:
    print("3 is present in the list")
else:
    print("3 is not present in the list")

# is "Hello" present
if "Hello" in myList:
    print("Hello is present in the list")
else:
    print("Hello is not present in the list")

The program will give us the following output.

3 is not present in the list
Hello is present in the list

In the next tutorial we are going to learn about useful list methods to work with lists.

See you there. Have fun coding :)

Python - List