Python Lists

A list is a value which contains multiple values in an ordered sequence. In a string the values are characters but in a list the values can be at any type. A list starts with an opening square bracket and ends with a closing square bracket. Values inside the list are also called items. Items are separated with commas. For example:

list1 = ["c", "python", "java", "javascript"]
list2 = [5, 6, 7, 8]

Just the string values are typed with quote characters to mark where the string begins and ends. Like string the list indices also start with 0. The items of a list don’t have to be the same type. A list can contain a string, a float, an integer and other data types also. For example:

list1 = ["python", 7, 3.75, True, None]

Accessing List Items

You can access the list items by referring to the index number.

Example:

list1 = ["python", 7, 3.75, True, None]
print(list1[0])
print(list1[3])

Output:

python
True

Just an index can get a single value from a list but by specifyling a range you can get several values from a list.

list1 = ["python", 7, 3.75, True, None]
print(list1[0:3])
print(list1[1:4])

['python', 7, 3.75]
[7, 3.75, True]

You can also ignore one or both of the indices on either side of the colon. Ignore the first side is just same as using 0 and ignore the right side will give the value to the end of the list.

list1 = ["python", 7, 3.75, True, None]
print(list1[:3])
print(list1[1:])

['python', 7, 3.75]
[7, 3.75, True, None]

Changing Values in a List

You can change a specific item use an index of a list.

Example:

list1 = ["python", 7, 3.75, True, None]
list1[0] = "programming"
print(list1)

Output:

['programming', 7, 3.75, True, None]

List Concatenation

There are several way in python to concatenate multiple lists. The easiest way is to using the + operator. It combines two list into a new list.

Example:

list1 = ["c", "python", "java"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)

Output:

['c', 'python', 'java', 1, 2, 3]

You can also replicate a list using * operator with a list and an integer value.

Example:

list1 = ["c", "python", "java"]
list2 = list1 * 3
print(list2)

Output:

['c', 'python', 'java', 'c', 'python', 'java', 'c', 'python', 'java']

Removing List Items

You can remove a list item using the del statement.

Example:

list1 = ["c", "python", "java"]
del list1[2]
print(list1)

Output:

['c', 'python']

You can also remove the list completely using the del statement.

Example:

list1 = ["c", "python", "java"]
del list1
print(list1)

Output:

Traceback (most recent call last):
  File "C:\Users\Hp\Desktop\py\python.py", line 3, in <module>
    print(list1)
NameError: name 'list1' is not defined

Note: Since the total tuple is deleted an error is raised in the output.

Length of a List

You can define the length of a list using the len() method.

Example:

list1 = ["c", "python", "java"]
print(len(list1))

Output:

3

List Methods

There are a set of built-in methods in python which you can use on lists.