List in Python, List example in python

List in Python

A list is a collection of items stored in a proper sequence. Unlike arrays in other languages (which store only similar items), Python lists can store similar and dissimilar items together.

Lists are ordered and mutable, which means we can add, modify, and delete elements dynamically.

Syntax of List

var = [item1, item2, item3]
x = [12, 23]

---

Add Elements

x.append(24)      # [12, 23, 24]

Delete Elements

del x[0]

Modify Elements

x[index] = value

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List Program to Implement All Operations

x = ["vegetable","rice","fruit","oil","flour"]

# Print using index
for i in range(0, len(x)):
    print(x[i])

# Print using for-each
for value in x:
    print(value)

# Slicing
print(x[3:])
print(x[2:4])
print(x[-4:-1])
print(x[-4])
print(x[:3])
print(x[:])

# Append
x.append("noodles")
print(x)

# Delete
del x[0]
print(x)

# Modify
x[4] = "maggi"
print(x)

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Another Example

x = [12, 23, 34, 11, 67, 89]

x.append(101)     # append
del x[0]          # delete
x[0] = 120        # modify

for i in range(0, len(x)):
    print(x[i])

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List Assignments

1. WAP to display prime elements in list
2. WAP to display nested list elements

   [12,21,[1,2,3,[4,5],6,7]]  
   [12,11,[2,5],[1,[1,2]]]

3. WAP to find max element in list
4. WAP to arrange list elements:

   [1,2,3,1,1,5,2,3,4,5]  
   Output → [1,1,1,2,2,3,3,4,5,5]

5. WAP to calculate factorial of even numbers and table of odd numbers in list

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Arithmetic Operations on List

Addition

a = [1,2,3]
b = [4,5,6]
c = a + b       # Combines lists
# Output: [1,2,3,4,5,6]

Multiplication

a * 2           # Repeats list elements

Program — Addition, Multiplication, IN and IS Operator

a = [1,2,3]
b = a * 2
print(b)

x = [1,2,3]
y = [4,5,6]
z = x + y
print(z)

del x[0]
print(x)

if 20 in a:
    print("Found")
else:
    print("NOT Found")

y = x
print(x)
print(y)

if x is y:
    print("equal")
else:
    print("not equal")

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Multidimensional or Nested List

A list inside another list is called a nested list or multidimensional list. It represents rows and columns like a matrix.

x = [[1,2,3],[4,5,6]]

for i in range(0,2):
    for j in range(0,3):
        print(x[i][j], end=" ")
    print()

---

Display Multidimensional List (variable-length rows)

x = [[1,2,3,4,5], [3,4,6,7], [3,3,3]]

for i in x:
    for j in i:
        print(j, end="")
    print()

---

Matrix Multiplication using List

x = [[1,2],[4,5]]
y = [[2,4],[1,2]]
z = [[int]*2, [int]*2]

for i in range(0,2):
    for j in range(0,2):
        s = 0
        for k in range(0,2):
            s = s + x[i][k] * y[k][j]
        z[i][j] = s
    print()

# Display output
for i in range(0,2):
    for j in range(0,2):
        print(z[i][j], end=" ")
    print()

---

Taking Input from User in List

x = []
size = int(input("number of elements: "))

for i in range(0, size):
    x.append(input("Enter item: "))

for i in range(0, len(x)):
    print(x[i])

---

Convert Multidimensional List into Single Dimension

y = [1, [2,3,[4,5]], [6,[7,8]]]

y1 = y[0:1]
y2 = y[1:2]
y21 = y2[0]
y22 = y21[0:2]
y23 = y21[2:3]
y24 = y23[0]
y3 = y[2:3]
y31 = y3[0]
y32 = y31[0:1]
y33 = y31[1:]
y34 = y33[0]

print(y34)
print(y1 + y22 + y24 + y32 + y34)

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More List Assignments

1. WAP to calculate sum of list elements
2. WAP to display prime elements in list
3. WAP to divide list into 3 sub-lists
4. WAP to reverse list
5. WAP to combine 3 lists
6. WAP to create marksheet using list
7. WAP to display unique elements
8. WAP to display repeated elements once
9. WAP to sort list in descending order
10. WAP to find max, second max, third max without sorting

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Predefined List Functions

• len()
• append()
• extend()
• remove()
• min()
• max()
• sort()
• reverse()
• index()
• count()
• list()

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Examples

x = [12,23,34,78,89,23,23,78]

print(len(x))
x.append(22)
print(x)
x.remove(23)
print(x)
x.index(12)
print(x.count(23))

y = [1,2,3]
x.extend(y)
print(x)

x.sort()
print(x)

x.reverse()
print(x)

print(max(x))
print(min(x))

z = (1,2,3)
print(list(z))

---

List Slicing on Nested List

l = [1,2,[3,4,5,[6,7]]]

A = l[0:2]
B = l[2:]
C = []
D = []

for i in B:
    for j in i:
        if type(j).__name__ == "int":
            C.append(j)
        else:
            for k in j:
                D.append(k)

lst = A + C + D
print(lst)