Introduction
- Data structures are basically structures which can hold some data together.
- They are used to store a collection of related data.
- There are built-in data structures in Python:
List
Tuple
Dictionary
List:-
- A list is a data structure that holds an ordered collection of items.
- A list can be composed by storing a sequence of different type of values separated by commas.
- The elements are stored in the index basis with starting index as 0.
- The elements are stored in the index basis with starting index as 0.
- The list of items should be enclosed in square brackets.
- Once a list is created, user can add, remove or search for items in the list.
- Python lists are mutable i.e., Python will not create a new list if we modify an element in the list.
Accessing List: A list can be created by putting the value inside the square bracket and separated by comma.
Syntax:
<list_name>=[value1,value2,value3,...,valuen];
Updating Lists:-
You can update single or multiple elements of lists by giving the slice on the left-hand side of the assignment operator.
Example:-
list = ['physics', 'chemistry', 1997, 2000]
print ("Value available at index 2 : ", list[2])
list[2] = 2001
print ("New value available at index 2 : ", list[2])
Delete List Elements:-
To remove a list element, you can use either the del statement if you know exactly which element(s) you are deleting.
Example:-
list = ['physics', 'chemistry', 1997, 2000]
print (list)
del list[2]
del list[2]
print ("After deleting value at index 2 : ", list)
Basic List Operations:-
Lists respond to the + and * operators much like strings; they mean concatenation and repetition here too, except that the result is a new list, not a string.
Indexing, Slicing and Matrixes
Since lists are sequences, indexing and slicing work the same way for lists as they do for strings. Assuming the following input −
L = ['C++'', 'Java', 'Python']
Hear ALL LIst OPeration Given
List Operations – cmp()
The cmp() method compares the elements of two lists.
Syntax:-
cmp(list1, list2)
Return value If elements are of the same type, perform the compare and return the result.
Example:-
list1, list2 = [123, 'xyz'], [456, 'abc']
print cmp(list1, list2) #-1
print cmp(list2, list1) #1
list3 = list2 + [786];
print cmp(list2, list3)#-1
List Operations – len()
The len() method returns the number of elements in the list.
Syntax:-
len(list)
Example:-
list1 = ['physics', 'chemistry', 'maths']
print (len(list1)) # 3
list2 = list(range(5)) #creates list of numbers between 0-4
list2 = list(range(5)) #creates list of numbers between 0-4
print (len(list2)) # 5
List Operations – max()
The max() method returns the elements from the list with maximum value.
Syntax:-
max(list)
Example:-
list1, list2 = ['C++','Java', 'Python'], [456, 700, 200]
print ("Max value element : ", max(list1)) # Python
print ("Max value element : ", max(list2)) #700
List Operations – min()
The min() method returns the elements from the list with minimum value.
Syntax:-
min(list)
Example:-
list1, list2 = ['C++','Java', 'Python'], [456, 700, 200]
print ("min value element : ", min(list1)) # C++
print ("min value element : ", min(list2)) # 200
List Operations – list()
The list() method takes sequence types and converts them to lists. This is used to convert a given tuple into list.
Syntax:-
list( seq )
Example:-
Tuple = (123, 'C++', 'Java', 'Python')
list1 = list(Tuple)
print ("List elements : ", list1)
str = "Hello World" list2 = list(str)
str = "Hello World" list2 = list(str)
print ("List elements : ", list2)
Output:-
List elements : [123, 'C++', 'Java', 'Python']
List elements : ['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd']
List Operations - append()
The append() method adds an item to the end of the list.
Syntax:-
list.append(item)
Example:-
List = ['Mathematics', 'chemistry', 1997, 2000]
List.append(20544) print(List)
Output:-
['Mathematics', 'chemistry', 1997, 2000, 20544]
List Operations: extend()
Extends the list by adding all items of a list (passed as an argument) to the end.
Syntax:-
list1.extend(list2)
Example:-
List1 = [1, 2, 3]
List2 = [2, 3, 4, 5]
List1.extend(List2) # Add List2 to List1
print(List1)
List2.extend(List1) #Add List1 to List2 now
print(List2)
Output:-
[1, 2, 3, 2, 3, 4, 5]
[2, 3, 4, 5, 1, 2, 3, 2, 3, 4, 5]
List Operations: insert()
Inserts the element to the list at the given index.
Syntax:-
list.insert(index, element)
Position mentioned should be within the range of List, as in this case between 0 and 4, elsewise would throw IndexError.
Example:-
List = ['Mathematics', 'chemistry', 1997, 2000]
# Insert at index 2 value 10087
List.insert(2,10087)
print(List)
Output:-
['Mathematics', 'chemistry', 10087, 1997, 2000]
List Operations: sum()
Calculates sum of all the elements of List.
Syntax:-
sum(list)
Example:-
List = [1, 2, 3, 4, 5]
print(sum(List))
Output:-
15
List Operations: remove()
searches for the given element in the list and removes the first matching element.
Syntax:-
list.remove(element)
Example:-
list1 = ['physics', 'Biology', 'chemistry', 'maths']
list1.remove('Biology')
print ("list now : ", list1)
list1.remove('maths')
print ("list now : ", list1)
Output:-
list now : ['physics', 'chemistry', 'maths']
list now : ['physics', 'chemistry']
List Operations: index()
searches an element in the list and returns its index/position.
Syntax:-
list.index(element)
Example:-
list1 = ['physics', 'chemistry', 'maths']
print ('Index of chemistry', list1.index('chemistry'))
print ('Index of C#', list1.index('C#'))
Output:-
Index of chemistry 1
Traceback (most recent call last):
File "test.py", line 3, in <module>
print ('Index of C#', list1.index('C#'))
ValueError: 'C#' is not in list
List Operations: count()
returns the number of occurrences of an element in a list.
Syntax:-
list.count(element)
Example:-
aList = [123, 'xyz', 'zara', 'abc', 123];
List Operations: pop()
removes and returns the element at the given index from the list.
Syntax:-
list.pop(index, element)
The parameter passed to the pop() method is optional. If no parameter is passed, the default index -1 is passed as an argument which returns the last element.
Example:-
list1 = ['physics', 'Biology', 'chemistry', 'maths']
list1.pop()
print ("list now : ", list1)
list1.pop(1)
print ("list now : ", list1)
Output:-
list now : ['physics', 'Biology', 'chemistry']
list now : ['physics', 'chemistry']
List Operations: reverse()
reverses the elements of a given list. Also it doesn't return any value.
Syntax:-
list.reverse()
The parameter passed to the pop() method is optional. If no parameter is passed, the default index -1 is passed as an argument which returns the last element.
Example:-
list1 = ['physics', 'Biology', 'chemistry', 'maths']
list1.reverse()
print ("list now : ", list1)
Output:-
list now : ['maths', 'chemistry', 'Biology', 'physics']
List Operations: sort()
sorts the elements of a given list in a specific order - Ascending or Descending.
Syntax:-
list.sort(key=..., reverse=...)
Above parameter is optional:
List Operations: remove()
searches for the given element in the list and removes the first matching element.
Syntax:-
list.remove(element)
Example:-
list1 = ['physics', 'Biology', 'chemistry', 'maths']
list1.remove('Biology')
print ("list now : ", list1)
list1.remove('maths')
print ("list now : ", list1)
Output:-
list now : ['physics', 'chemistry', 'maths']
list now : ['physics', 'chemistry']
List Operations: index()
searches an element in the list and returns its index/position.
Syntax:-
list.index(element)
Example:-
list1 = ['physics', 'chemistry', 'maths']
print ('Index of chemistry', list1.index('chemistry'))
print ('Index of C#', list1.index('C#'))
Output:-
Index of chemistry 1
Traceback (most recent call last):
File "test.py", line 3, in <module>
print ('Index of C#', list1.index('C#'))
ValueError: 'C#' is not in list
List Operations: count()
returns the number of occurrences of an element in a list.
Syntax:-
list.count(element)
Example:-
aList = [123, 'xyz', 'zara', 'abc', 123];
print ("Count for 123 : ", aList.count(123))
print ("Count for zara : ", aList.count('zara'))
Output:-
Count for 123 : 2
Count for zara : 1
List Operations: pop()
removes and returns the element at the given index from the list.
Syntax:-
list.pop(index, element)
The parameter passed to the pop() method is optional. If no parameter is passed, the default index -1 is passed as an argument which returns the last element.
Example:-
list1 = ['physics', 'Biology', 'chemistry', 'maths']
list1.pop()
print ("list now : ", list1)
list1.pop(1)
print ("list now : ", list1)
Output:-
list now : ['physics', 'Biology', 'chemistry']
list now : ['physics', 'chemistry']
List Operations: reverse()
reverses the elements of a given list. Also it doesn't return any value.
Syntax:-
list.reverse()
The parameter passed to the pop() method is optional. If no parameter is passed, the default index -1 is passed as an argument which returns the last element.
Example:-
list1 = ['physics', 'Biology', 'chemistry', 'maths']
list1.reverse()
print ("list now : ", list1)
Output:-
list now : ['maths', 'chemistry', 'Biology', 'physics']
List Operations: sort()
sorts the elements of a given list in a specific order - Ascending or Descending.
Syntax:-
list.sort(key=..., reverse=...)
Above parameter is optional:
reverse - If true, the sorted list is reversed (or sorted in Descending order)
Syntax:-
sorted(key=..., reverse=...)
difference between sort() and sorted() is: sort() doesn't return any value while, sorted() returns an iterable list.
List Operations: sorted()
The sorted() method sorts the elements of a given iterable in a specific order - Ascending or Descending.
Syntax:-
sorted(iterable[, key][, reverse])
sorted() Parameters
iterable - sequence (string, tuple, list) or collection (dictionary)
reverse (Optional) - If true, the sorted list is reversed (or sorted in Descending order)
key (Optional) - function that serves as a key for the sort comparison
Example:-
# vowels list
pyList = ['e', 'a', 'u', 'o', 'i']
print(sort(pyList))
# string
pyString = 'Python'
List2 = sorted(pyString)
# vowels
tuple pyTuple = ('e', 'a', 'u', 'o', 'i')
print(sorted(pyTuple))
Output:-
['a', 'e', 'i', 'o', 'u']
['P', 'h', 'n', 'o', 't', 'y']
['a', 'e', 'i', 'o', 'u']
Syntax:-
sorted(key=..., reverse=...)
difference between sort() and sorted() is: sort() doesn't return any value while, sorted() returns an iterable list.
List Operations: sorted()
The sorted() method sorts the elements of a given iterable in a specific order - Ascending or Descending.
Syntax:-
sorted(iterable[, key][, reverse])
sorted() Parameters
iterable - sequence (string, tuple, list) or collection (dictionary)
reverse (Optional) - If true, the sorted list is reversed (or sorted in Descending order)
key (Optional) - function that serves as a key for the sort comparison
Example:-
# vowels list
pyList = ['e', 'a', 'u', 'o', 'i']
print(sort(pyList))
# string
pyString = 'Python'
List2 = sorted(pyString)
# vowels
tuple pyTuple = ('e', 'a', 'u', 'o', 'i')
print(sorted(pyTuple))
Output:-
['a', 'e', 'i', 'o', 'u']
['P', 'h', 'n', 'o', 't', 'y']
['a', 'e', 'i', 'o', 'u']
List Operations: copy()
returns a copy of the list.
Soft copy
Deep copy
Soft copy: A list can be copied with = operator but when user modify the new_list, the old_list is also modified.
Deep copy: So copy() method keeps original list unchanged when the new list is modified.
Syntax:-
new_list = copy.deepcopy(old_list)
Example:-
import copy
li1 = [1, 2, 3]
li2 = copy.deepcopy(li1)
print ("The original elements before deep copying")
for i in range(0,len(li1)):
print (li1[i],end=" ")
li2[2] = 7
print ("The new list of elements after deep copying ")
for i in range(0,len( li1)):
print (li2[i],end=" ")
print ("The original elements after deep copying")
for i in range(0,len( li1)):
print (li1[i],end=" ")
List Operations: clear()
removes all items from the list.
Syntax:-
list.clear()
Example:-
fruits = ['apple', 'banana', 'cherry', 'orange'] fruits.clear()
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li1 = [1, 2, 3]
li2 = copy.deepcopy(li1)
print ("The original elements before deep copying")
for i in range(0,len(li1)):
print (li1[i],end=" ")
li2[2] = 7
print ("The new list of elements after deep copying ")
for i in range(0,len( li1)):
print (li2[i],end=" ")
print ("The original elements after deep copying")
for i in range(0,len( li1)):
print (li1[i],end=" ")
List Operations: clear()
removes all items from the list.
Syntax:-
list.clear()
Example:-
fruits = ['apple', 'banana', 'cherry', 'orange'] fruits.clear()
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