Some Basic Python List Programs-3


Python program to remove duplicates from a list

list1 = [2, 6, 9, 8, 4, 8, 6, 6, 5, 7, 2, 4]

#using list comprehension
list2 = [] 
[list2.append(ele) for ele in list1 if ele not in list2] 
print(list2) 
#Output: [2, 6, 9, 8, 4, 5, 7]

#using list comprehension and enumerate()
list3 = [ele for i,ele in enumerate(list1) if ele not in list1[:i]]
print(list3) 
#Output: [2, 6, 9, 8, 4, 5, 7] 

#using set() 
list4 = list(set(list1))
print(list4)
#Output: [2, 4, 5, 6, 7, 8, 9]
  • List comprehension is a compact method that defines a list and its contents at the same time. The basic syntax of list comprehension consists of a square bracket with an expression that is executed for each element along with for loop to iterate over each element. Read more: List Comprehension in Python – Explained with Examples
  • The append() built-in list method adds the element of the iterable passed as an argument to the end of the list.
  • The built-in enumerate() function assigns an index to each element in an iterable and each time returns a tuple of the form (index, element). Read more: What is indexing, iterating and enumerating in python?
  • Slicing extracts a subset of elements from a sequence. It mainly uses three parameters strat, stop, and step enclosed in square brackets []. Read more: Slicing in python
  • The set() built-in method creates a set of the iterable passed. A set is an unordered collection of immutable and unique elements in python.
  • The list() built-in method takes an iterable and creates a new list of its elements.

Python program to check if one list is a subset of another list

list1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
list2 = [5, 8, 6, 4]

#using all()
if all(ele in list1 for ele in list2):
    print(f"{list2} is a sublist of {list1}")
else:
    print(f"{list2} is not a sublist of {list1}") 
#Output: [5, 8, 6, 4] is a sublist of [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

#using issubset() 
if set(list2).issubset(set(list1)):
    print(f"{list2} is a sublist of {list1}") 
else:
    print(f"{list2} is not a sublist of {list1}") 
#Output: [5, 8, 6, 4] is a sublist of [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

#using & operator
if set(list2) & set(list1) == set(list2):
    print(f"{list2} is a sublist of {list1}") 
else:
    print(f"{list2} is not a sublist of {list1}") 
#Output: [5, 8, 6, 4] is a sublist of [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  • The all() built-in method returns True If all the elements in the iterable passed are true else it returns False.
  • Python treats everything as an object and objects are always true in python. However, null values, None, 0, empty data types are observed as false in python.
  • The format() built-in string method returns a formatted representation of the string controlled by the format specifier. The prefix f before a string tells Python that the string is a format string. The replacement fields are expressions enclosed in curly brackets in a format string. They are evaluated at run time and then formatted.
  • The issubset() built-in method returns True if all the elements of a set are present in the iterable passed else it returns False.
  • A set in python represents a mathematical notion of a set and performs set operations like union, intersection, difference, etc. The ‘&’ operator executes the intersection between sets. Read more: Set Data Type in Python

Python program to check if all elements in a List are same

list = ['Python', 'Python', 'Python', 'Python', 'Python', 'Python']

#using all()
if all(ele == list[0] for ele in list):
    print("All the elements in the list are same")
else:
    print("All the elements in the list are different")
#Output: All the elements in the list are same

#using count() 
if list.count(list[0]) == len(list):
    print("All the elements in the list are same") 
else: 
    print("All the elements in the list are different")
#Output: All the elements in the list are same

#using set()
if len(set(list)) == 1:
    print("All the elements in the list are same") 
else: 
    print("All the elements in the list are different")
#Output: All the elements in the list are same
  • The count() built-in list method returns the number of times a specified element appears in the list.

Python program to insert a given string at the beginning of all elements in a list

list1 = [1, 2, 3, 4, 5]
str1 = 'number'

#using list comprehension and format()
str2 = str1 + '{}'
list2 = [str2.format(ele) for ele in list1]
print(list2)
#Output: ['number1', 'number2', 'number3', 'number4', 'number5']

#using list comprehension and % operator
str3 = str1 + '% s'
list3 = [str3 % ele for ele in list1]
print(list3)
#Output: ['number1', 'number2', 'number3', 'number4', 'number5']

#using map() and format()
str4 = str1 + '{}'
list4 = list(map(str4.format, list1))
print(list4)
#Output: ['number1', 'number2', 'number3', 'number4', 'number5']
  • The % operator is a format place holder for C-style formatting in a string. The “s” after the “%” signifies that the variable inserting in that position is of the string type.
  • The built-in map() function applies a given function to each element of an iterable and returns a list of the results.

Python program to pair consecutive elements in a list

list1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

#using list comprehension
list2 = [[list1[i], list1[i+1]] for i in range(len(list1)-1)]
print(list2)
#Output: [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9]]

#using zip()
list3 = list(zip(list1, list1[1:]))
print(list3)
#Output: [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 6), (6, 7), (7, 8), (8, 9)]
  • The zip() built-in method returns an iterator of tuples, grouping the similar index of multiple sequences so that they can be used as a single entity.

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