Python Data Type - List

Creating List

# A simple List
l1 = [1, 2, 3, 4]
l2 = ["a", "b", "c"]

# List inside list
l3 = ["e", "f", [1, 2, 3], "g"]

# Tuple inside list
l4 = [5, 6, ("x", "y", "z"), 7, 8]

# Dictionary inside List
l5 = ["p", "q", {"r": 11, "s": 12}, "t"]

Accessing elements of List

print(l1[2])
print(l1[-2])
print(l2[1:])
print(l3[2][1])  # Prints 2
print(l4[2][0])  # Prints x
print(l5[2]["s"])  # Prints 12

Updating the List: Python List are Mutable

l1[2] = 33  # Replaces 3 with 33
l3[2][1] = 22  # Replaces 2 with 22

Deleting elements from the list

# Deleting the whole list
del l1

# Deleting only specific elements from the list

# 1. Using element
l2.remove("a")

# 2. Using index number of element
del l3[1]

l3.pop(0)
print(l4.pop(0))

Adding extra elements in the list

# Adding elements at last
l4.append(9)

# Adding elements at specific place using index number
l5.insert(1, "qq")

List Operations and Built-in Functions

# Multiplication
print(l4 \* 3) # Prints l4 3 times

# Membership
# Checks whether 5 is in l4 or not return either true or false
print(5 in l4) 

# List Comprehension
# Creates list having elements from 1 to 19 that are divisible 2
l6 = [i for i in range(1, 20) if i % 2 == 0] 

# Length
print(len(l6))

# Max
print(max(l6))

# Min
print(min(l6))

# Sum: Gives the sum of elements of list
print(sum(l6))

# Sort
l7 = [3, 2, 1]
print(sorted(l7)) # Print sorted version of l7 i.e prints [1,2,3]

# List: Converts any other data type into List
l8 = list("abcde") # Creates List as ['a', 'b', 'c', 'd', 'e']

# any(): It returns True if even one item in the Python list has a True value.
print(any(["a" in ["a", "b"], "b" not in [1, 2, 3]])) # Prints True
print(any([])) # Returns False for empty list

# all(): It returns True if all items in the list have a True value
print(all(["a" in ["a", "b"], "b" in [1, 2, 3]])) # Prints false
print(all([])) # Returns True for empty list

# Clear
l9 = [1, 2, 3, 4, 5]
l9.clear() # It clears the whole list and makes it empty

# index()
print(l7.index(2)) # Gives the index number of 2 from l7

# count()
print(l7.count(2)) # it counts how many times the element is repeated

# reverse()
print(l7.reverse()) # returns reverse of the list l7

List map

Maps every element of list with the given function

>>> l = [1, 2, 3, 4]
>>> def fun(a):
...     return a*a
...
>>> map(fun, l)
<map object at 0x0000023459D6B8E0>
>>> list(map(fun, l))
[1, 4, 9, 16]