Lists are used in python to store data when we need to access them sequentially. In this article, we will discuss how we can create a list of lists in python. We will also implement programs to perform various operations like sorting, traversing, and reversing a list of lists in python.
Table of Contents
- What Is a List of Lists in Python?
- Create a List of Lists in Python
- List of Lists Using the append() Method in Python
- Create List of Lists Using List Comprehension in Python
- Access Elements in a List of Lists in Python
- Traverse a List of Lists in Python
- Delete an Element From a List of Lists in Python
- Delete an Element From a List of Lists Using the pop() Method
- Remove an Element From a List of Lists Using the remove() Method
- Flatten List of Lists in Python
- Reverse List of Lists in Python
- Reverse the Order of Inner List in List of Lists in Python
- Reversing the Order of Elements of Inner List in List of Lists in Python
- Sort List of Lists in Python
- Sort List of Lists in Python Using the sort() Method
- Sorting List of Lists in Python Using the sorted() Function
- Concatenate Two Lists of Lists in Python
- Copy List of Lists in Python
- Shallow Copy List of Lists in Python
- Deep Copy List of Lists in Python
- Conclusion
What Is a List of Lists in Python?
A list of lists in python is a list that contains lists as its elements. Following is an example of a list of lists.
myList=[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Here, myList contains five lists as its elements. Hence, it is a list of lists.
Create a List of Lists in Python
To create a list of lists in python, you can use the square brackets to store all the inner lists. For instance, if you have 5 lists and you want to create a list of lists from the given lists, you can put them in square brackets as shown in the following python code.
list1 = [1, 2, 3, 4, 5]print("The first list is:", list1)list2 = [12, 13, 23]print("The second list is:", list2)list3 = [10, 20, 30]print("The third list is:", list3)list4 = [11, 22, 33]print("The fourth list is:", list4)list5 = [12, 24, 36]print("The fifth list is:", list5)myList = [list1, list2, list3, list4, list5]print("The list of lists is:")print(myList)Output:
The first list is: [1, 2, 3, 4, 5]The second list is: [12, 13, 23]The third list is: [10, 20, 30]The fourth list is: [11, 22, 33]The fifth list is: [12, 24, 36]The list of lists is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]In the above example, you can observe that we have created a list of lists using the given lists.
List of Lists Using the append() Method in Python
We can also create a list of lists using the append() method in python. The append() method, when invoked on a list, takes an object as input and appends it to the end of the list. To create a list of lists using the append() method, we will first create a new empty list. For this, you can either use the square bracket notation or the list() constructor. The list() constructor, when executed without input arguments, returns an empty list.
After creating the empty list, we can append all the given lists to the created list using the append() method to create a list of lists in python as shown in the following code snippet.
list1 = [1, 2, 3, 4, 5]print("The first list is:", list1)list2 = [12, 13, 23]print("The second list is:", list2)list3 = [10, 20, 30]print("The third list is:", list3)list4 = [11, 22, 33]print("The fourth list is:", list4)list5 = [12, 24, 36]print("The fifth list is:", list5)myList = []myList.append(list1)myList.append(list2)myList.append(list3)myList.append(list4)myList.append(list5)print("The list of lists is:")print(myList)Output:
The first list is: [1, 2, 3, 4, 5]The second list is: [12, 13, 23]The third list is: [10, 20, 30]The fourth list is: [11, 22, 33]The fifth list is: [12, 24, 36]The list of lists is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]If you want to create a list of lists like a 2-d array using only integer data types, you can use nested for loops with the append()method to create a list of lists.
In this approach, we will first create a new list, say myList. After that, we will use nested for loop to append other lists to myList. In the outer for loop of the nested loop, we will create another empty list, say tempList. In the inner for loop, we will append the numbers to tempList using the append() method.
After appending the numbers to tempList, we will get a list of integers. After that, we will come to the outer for loop and will append tempList to myList. In this way, we can create a list of lists.
For instance, suppose that we have to create a 3×3 array of numbers. For this, we will use the range() function and the for loop to create a list of lists in python as follows.
myList = []for i in range(3): tempList = [] for j in range(3): element = i + j tempList.append(element) myList.append(tempList)print("The list of lists is:")print(myList)Output:
The list of lists is:[[0, 1, 2], [1, 2, 3], [2, 3, 4]]Create List of Lists Using List Comprehension in Python
Instead of using the for loop, you can use list comprehension with the range() function to create a list of lists in a concise way as shown in the following example.
myList = [[i+j for i in range(3)] for j in range(3)]print("The list of lists is:")print(myList)Output:
The list of lists is:[[0, 1, 2], [1, 2, 3], [2, 3, 4]]Access Elements in a List of Lists in Python
We can access the contents of a list using the list index. In a flat list or 1-d list, we can directly access the list elements using the index of the elements. For instance, if we want to use positive values as the index for the list elements, we can access the 1st item of the list using index 0 as shown below.
myList = [1, 2, 3, 4, 5]print("The list is:")print(myList)print("The first item of the list is:")print(myList[0])Output:
The list is:[1, 2, 3, 4, 5]The first item of the list is:1Similarly, if we use the negative values as the list indices, we can access the last element of the list using the index -1 as shown below.
myList = [1, 2, 3, 4, 5]print("The list is:")print(myList)print("The last item of the list is:")print(myList[-1])Output:
The list is:[1, 2, 3, 4, 5]The last item of the list is:5If you want to access the inner lists from a list of lists, you can use list indices in a similar way as shown in the above example.
If you are using positive numbers as list indices, you can access the first inner list from the list of lists using index 0 as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The list of lists is:")print(myList)print("The first item of the nested list is:")print(myList[0])Output:
The list of lists is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The first item of the nested list is:[1, 2, 3, 4, 5]Similarly, if you are using negative numbers as list indices, you can access the last inner list from the list of lists as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The list of lists is:")print(myList)print("The last item of the nested list is:")print(myList[-1])Output:
The list of lists is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The last item of the nested list is:[12, 24, 36]To access the elements of the inner lists, you need to use double square brackets after the list name. Here, the first square bracket denotes the index of the inner list, and the second square bracket denotes the index of the element in the inner list.
For example, you can access the third element of the second list from the list of lists using square brackets as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The list of lists is:")print(myList)print("The third element of the second inner list is:")print(myList[1][2])Output:
The list of lists is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The third element of the second inner list is:23Traverse a List of Lists in Python
To traverse the elements of a list of lists, we can use a for a loop. To print the inner lists, we can simply iterate through the list of lists as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]for inner_list in myList: print(inner_list)Output:
[1, 2, 3, 4, 5][12, 13, 23][10, 20, 30][11, 22, 33][12, 24, 36]Instead of printing the whole list while traversing the list of lists, we can also print the elements of the list. For this, we will use another for loop in addition to the for loop shown in the previous example. In the inner for loop, we will iterate through the inner lists and print their elements as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]for inner_list in myList: for element in inner_list: print(element, end=",") print("")Output:
1,2,3,4,5,12,13,23,10,20,30,11,22,33,12,24,36,Delete an Element From a List of Lists in Python
To delete an inner list from a list of lists, we can use different methods of list-objects.
Delete an Element From a List of Lists Using the pop() Method
We can use the pop() method to delete the last item from the list of lists. The pop() method, when invoked on the list of lists, deletes the last element and returns the list present at the last position. We can understand this using a simple example shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.pop()print("The modified list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The modified list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33]]To delete any other inner list, we will need to know its index. For instance, we can delete the second element of the list of lists using the pop() method. For this, we will invoke the pop() method on the list and will pass the index of the second list i.e. 1 to the pop() method. After execution, the pop() method will delete the second inner list from the list of lists and will return it as shown in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.pop(1)print("The modified list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The modified list is:[[1, 2, 3, 4, 5], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Remove an Element From a List of Lists Using the remove() Method
If we know the element that has to be deleted, we can also use the remove() method to delete an inner list. The remove() method, when invoked on a list, takes the element to be deleted as its input argument. After execution, it deletes the first occurrence of the element passed as the input argument. To delete any inner list, we can use the remove() method as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.remove([1, 2, 3, 4, 5])print("The modified list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The modified list is:[[12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Flatten List of Lists in Python
Sometimes, we need to flatten a list of lists to create a 1-d list. To flatten the list of lists, we can use a for loop and the append() method. In this approach, we will first create an empty list say outputList.
After creating outputList, we will use a nested for loop to traverse the list of lists. In the outer for loop, we will select an inner list. After that, we will traverse the elements of the inner list in the inner for loop. In the inner for loop, we will invoke the append() method on outputList and will pass the elements of the inner for loop as an input argument to the append() method.
After execution of the for loops, we will get a flat list created from the list of lists as shown in the following code.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = []for inner_list in myList: for element in inner_list: outputList.append(element)print("The flattened list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The flattened list is:[1, 2, 3, 4, 5, 12, 13, 23, 10, 20, 30, 11, 22, 33, 12, 24, 36]Instead of using the for loop, you can also use list comprehension to flatten a list of lists as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = [x for l in myList for x in l]print("The flattened list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The flattened list is:[1, 2, 3, 4, 5, 12, 13, 23, 10, 20, 30, 11, 22, 33, 12, 24, 36]Reverse List of Lists in Python
We can reverse a list of lists in two ways. One approach is to reverse the order of the inner lists only and leave the order of the elements in the inner lists intact. Another approach is to reverse the order of the elements in the inner lists too.
Reverse the Order of Inner List in List of Lists in Python
To simplify reverse the order of the inner lists, we will first create an empty list, say outputList. After that, we will traverse through the list of lists in reverse order. While traversal, we will append the inner lists to outputList. In this way, we will get the reversed list of lists outputList after the execution of the for loop. You can observe this in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = []listlen = len(myList)for i in range(listlen): outputList.append(myList[listlen - 1 - i])print("The reversed list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The reversed list is:[[12, 24, 36], [11, 22, 33], [10, 20, 30], [12, 13, 23], [1, 2, 3, 4, 5]]Instead of using the for loop, you can use the reverse() method to reverse the list of lists. The reverse() method, when invoked on a list, reverses the order of the elements in the list. When we will invoke the reverse() method on the list of lists, it will reverse the order of the inner lists as shown in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.reverse()print("The reversed list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The reversed list is:[[12, 24, 36], [11, 22, 33], [10, 20, 30], [12, 13, 23], [1, 2, 3, 4, 5]]In the above approach, the original list is modified. However, that wasn’t the situation in the previous example. Thus, you can choose an approach depending on whether you have to modify the original list or not.
Reversing the Order of Elements of Inner List in List of Lists in Python
In addition to reversing the order of the inner lists, you can also reverse the order of the elements in the inner lists. For this, we will first create an empty list, say outputList. After that, we will traverse through the list of lists in reverse order using a for a loop. Inside the for loop, we will create an empty list, say tempList. After that, we will traverse through the elements of the inner list in reverse order using another for loop. While traversing the elements of the inner list, we will append the elements to the tempList. Outside the inner loop, we will append the tempList to outputList.
After execution of the for loops, we will get a list with all the elements in reverse order as shown in the following code.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = []listlen = len(myList)for i in range(listlen): tempList = [] currList = myList[listlen - 1 - i] innerLen = len(currList) for j in range(innerLen): tempList.append(currList[innerLen - 1 - j]) outputList.append(tempList)print("The reversed list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The reversed list is:[[36, 24, 12], [33, 22, 11], [30, 20, 10], [23, 13, 12], [5, 4, 3, 2, 1]]Instead of using the for loop to reverse the elements of the inner lists, you can use the reverse() method as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = []listlen = len(myList)for i in range(listlen): myList[listlen - 1 - i].reverse() outputList.append(myList[listlen - 1 - i])print("The reversed list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The reversed list is:[[36, 24, 12], [33, 22, 11], [30, 20, 10], [23, 13, 12], [5, 4, 3, 2, 1]]Here, we have first reversed the inner list inside the for loop. After that, we have appended it to outputList. In this way, we have obtained the list of lists in which the inner lists, as well as the elements of the inner lists, are present in the reverse order as compared to the original list.
Sort List of Lists in Python
To sort a list of lists in python, we can use the sort() method or the sorted function.
Sort List of Lists in Python Using the sort() Method
The sort() method, when invoked on a list, sorts the elements of the list in increasing order. When we invoke the sort() method on a list of lists, it sorts the inner lists according to the first element of the inner lists.
In other words, the inner list whose first element is smallest among the first element of all the inner lists is assigned the first position in the list of lists. Similarly, the inner list whose first element is largest among the first element of all the inner lists is assigned the last position.
Also, if two inner lists have the same element at the first position, their position is decided on the basis of the second element. If the second element of the inner lists is also the same, the position of the lists will be decided on the basis of the third element, and so on. You can observe this in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.sort()print("The sorted list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[1, 2, 3, 4, 5], [10, 20, 30], [11, 22, 33], [12, 13, 23], [12, 24, 36]]You can also change the behavior of the sort() method. For this, you can use the ‘key’ parameter of the sort() method. The ‘key’ method takes an operator or a function as an input argument. For example, if you want to sort the list of lists according to the third element of the inner lists, you can pass an operator that uses the third element of the inner list as follows.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.sort(key=lambda x: x[2])print("The sorted list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]If you want to sort the list of lists according to the last elements of the inner lists, you can do it as follows.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.sort(key=lambda x: x[-1])print("The sorted list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Similarly, if you want to sort the list of lists according to the length of the inner lists, you can pass the len() function to the parameter ‘key’ of the sort() method. After execution, the sort() method will sort the list of lists using the length of the inner lists. You can observe this in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)myList.sort(key=len)print("The sorted list is:")print(myList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36], [1, 2, 3, 4, 5]]Sorting List of Lists in Python Using the sorted() Function
If you are not allowed to modify the original list of lists, you can use the sorted() function to sort a list of lists. The sorted() function works in a similar manner to the sort() method. However, instead of sorting the original list, it returns a sorted list.
To sort a list of lists, you can pass the list to the sorted() function. After execution, the sorted() function will return the sorted list as shown in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = sorted(myList)print("The sorted list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[1, 2, 3, 4, 5], [10, 20, 30], [11, 22, 33], [12, 13, 23], [12, 24, 36]]You can also use the key parameter to sort the list of lists using the sorted() function. For instance, you can sort the list of lists according to the third element of the inner lists using the sorted() function as shown below.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = sorted(myList, key=lambda x: x[2])print("The sorted list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]If you want to sort the list of lists according to the last elements of the inner lists, you can do it as follows.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = sorted(myList, key=lambda x: x[-1])print("The sorted list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Similarly, if you want to sort the list of lists according to the length of the inner lists, you can pass the len() function to the parameter ‘key’ of the sorted() function. After execution, the sorted() function will return the sorted list of lists using the length of the inner lists. You can observe this in the following example.
myList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = sorted(myList, key=len)print("The sorted list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The sorted list is:[[12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36], [1, 2, 3, 4, 5]]Concatenate Two Lists of Lists in Python
If you are given two lists of lists and you want to concatenate the list of lists, you can do it using the + operator as shown below.
list1 = [[1, 2, 3, 4, 5], [12, 13, 23]]list2 = [[10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The first list is:")print(list1)print("The second list is:")print(list2)print("The concatenated list is:")myList = list1 + list2print(myList)Output:
The first list is:[[1, 2, 3, 4, 5], [12, 13, 23]]The second list is:[[10, 20, 30], [11, 22, 33], [12, 24, 36]]The concatenated list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Here, the inner elements of both lists are concatenated into a single list of lists.
Copy List of Lists in Python
To copy a list of lists in python, we can use the copy() and the deepcopy() method provided in the copy module.
Shallow Copy List of Lists in Python
The copy() method takes a nested list as an input argument. After execution, it returns a list of lists similar to the original list. You can observe this in the following example.
import copymyList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = copy.copy(myList)print("The copied list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The copied list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The operation discussed in the above example is called shallow copy. Here, the inner elements in the copied list and the original list point to the same memory location. Thus, whenever we make a change in the copied list, it is reflected in the original list. Similarly, if we make a change in the original list, it is reflected in the copied list. To avoid this, you can use the deepcopy() method.
Deep Copy List of Lists in Python
The deepcopy() method takes a nested list as its input argument. After execution, it creates a copy of all the elements of the nested list at a different location and then returns the copied list. Thus, whenever we make a change in the copied list, it is not reflected in the original list. Similarly, if we make a change in the original list, it is not reflected in the copied list. You can observe this in the following example.
import copymyList = [[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]print("The original list is:")print(myList)outputList = copy.deepcopy(myList)print("The copied list is:")print(outputList)Output:
The original list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]The copied list is:[[1, 2, 3, 4, 5], [12, 13, 23], [10, 20, 30], [11, 22, 33], [12, 24, 36]]Conclusion
In this article, we have discussed the list of lists in python. We have discussed how we can perform various operations on a list of lists. We have also discussed how shallow copy and deep copy work with a list of lists. Additionally, we have discussed how to sort, reverse, flatten, and traverse a list of lists in python, To know more about the python programming language, you can read this article on dictionary comprehension in python. You might also like this article on file handling in python.
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FAQs
What does list [:] Do Python? ›
Definition and Usage. The list() function creates a list object. A list object is a collection which is ordered and changeable. Read more about list in the chapter: Python Lists.
How do I get a list of lists in Python? ›To create a list of lists in python, you can use the square brackets to store all the inner lists. For instance, if you have 5 lists and you want to create a list of lists from the given lists, you can put them in square brackets as shown in the following python code.
What is a list of lists in Python? ›A list of lists is a list where each element is a list by itself. The List is one of the 4 built-in data types in Python. One can learn more about other Python data types here.
How do I find out how many lists are in a list Python? ›There is a built-in function called len() for getting the total number of items in a list, tuple, arrays, dictionary, etc. The len() method takes an argument where you may provide a list and it returns the length of the given list.
How does list list work? ›A List is an ordered Collection. Lists may contain duplicate elements. In addition to the operations inherited from Collection , the list interface includes operations for the following: Positional access (random access): manipulates elements based on their numerical position in the list.
How do you create a list in Python? ›To create a list in Python, we use square brackets ( [] ). Here's what a list looks like: ListName = [ListItem, ListItem1, ListItem2, ListItem3, ...] Note that lists can have/store different data types.
How do I turn a list into a list of lists? ›- Using for loop. This is a very straight forward approach in which we create for loop to read each element. ...
- With split. In this approach we use the split function to extract each of the elements as they are separated by comma. ...
- Using map.
Using the * symbol to print a list in Python. To print the contents of a list in a single line with space, * or splat operator is one way to go. It passes all of the contents of a list to a function. We can print all elements in new lines or separated by space and to do that, we use sep=”\n” or sep=”, ” respectively.
How do I get a list of values from a list of keys in Python? ›Method 1: Get dictionary keys as a list using dict.
The dict. keys() method in Python Dictionary, returns a view object that displays a list of all the keys in the dictionary in order of insertion.
Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.
What are examples of lists? ›
A list is an ordered data structure with elements separated by a comma and enclosed within square brackets. For example, list1 and list2 shown below contains a single type of data. Here, list1 has integers while list2 has strings. Lists can also store mixed data types as shown in the list3 here.
What are the three types of lists? ›- unordered list — used to group a set of related items in no particular order.
- ordered list — used to group a set of related items in a specific order.
- description list — used to display name/value pairs such as terms and definitions.
Using Len() function to Get the Number of Elements
We can use the len( ) function to return the number of elements present in the list.
If you want to count multiple items in a list, you can call count() in a loop. This approach, however, requires a separate pass over the list for every count() call; which can be catastrophic for performance. Use couter() method from class collections , instead.
How to count elements in list in Python without count function? ›The most straightforward way to get the number of elements in a list is to use the Python built-in function len() . As the name function suggests, len() returns the length of the list, regardless of the types of elements in it.
How do you add a variable to a list in Python? ›- append() : append the element to the end of the list.
- insert() : inserts the element before the given index.
- extend() : extends the list by appending elements from the iterable.
- List Concatenation: We can use the + operator to concatenate multiple lists and create a new list.
To insert a list item at a specified index, use the insert() method.
Is list making good? ›Writing a daily gratitude list helps you consciously focus on what's good in your life, and can really shift your thinking. And often, the process of writing a list tackles procrastination head-on and subsequently boosts productivity. “We often put off the things that we need to do because we don't know where to start.
How do I manually create a list in Python? ›To initialize a list in Python assign one with square brackets, initialize with the list() function, create an empty list with multiplication, or use a list comprehension. The most common way to declare a list in Python is to use square brackets.
How do we create a list? ›- Tap Blank List, then give it a Name and a Description.
- Choose a color and an icon.
- Choose whether to save it under My Lists or on a specific SharePoint site.
- Tap Create. ...
- To add a column, tap More, then tap Add New Column.
- Choose the type of column data you want, then define the columns settings.
How do I convert a single list to multiple lists in Python? ›
Thus, converting the whole list into a list of lists. Use another list 'res' and a for a loop. Using split() method of Python we extract each element from the list in the form of the list itself and append it to 'res'. Finally, return 'res'.
How do I turn a list into an array? ›- Initialize an ArrayList.
- Add elements to the List through the list. ...
- Create an Array with the same size as the list.
- Convert the List into an Array by using the variable name of the array created in step 3 as an argument.
- Print the contents of the Array.
- Using numpy.array() This function of the numpy library takes a list as an argument and returns an array that contains all the elements of the list. See the example below: import numpy as np. ...
- Using numpy. asarray() This function calls the numpy.array() function inside itself.
To convert a list to a string, use Python List Comprehension and the join() function. The list comprehension will traverse the elements one by one, and the join() method will concatenate the list's elements into a new string and return it as output.
How can I get a list of specific field values from objects stored in a list? ›- Create a inner class with required variables. ...
- Create a List of the inner class created above and dont forget to encapsulate it. ...
- Get the value stored to the list as a inner class object. ...
- create a DATAMODEL and push the list to the datamodel. ...
- get the warpped data to another list.
count() to check if the list contains. Another built-in method in Python, count() returns the number of times the passed element occurs in the list. If the element is not there in the list then the count() will return 0. If it returns a positive integer greater than 0, it means the list contains the element.
What will list D keys ()) return? ›d. keys() Returns a list of keys in a dictionary.
How do I get a list of values from a list of dictionary? ›To obtain the list, we can utilise dictionary. values() in conjunction with the list() function. The values() method is used to access values from the key: value pairs and the values are then converted to a list using the list() function.
How to find the values of a key in a list of dictionaries in Python? ›- (1) Using a list() function: my_list = list(my_dict.values())
- (2) Using a List Comprehension: my_list = [i for i in my_dict.values()]
- (3) Using For Loop: my_list = [] for i in my_dict.values(): my_list.append(i)
An example of the three list types, which are unordered list, ordered list, and definition list.
How many methods does list have? ›
The List interface provides four methods for positional (indexed) access to list elements. Lists (like Java arrays) are zero based. Note that these operations may execute in time proportional to the index value for some implementations (the LinkedList class, for example).
What is the use of (*) operator in list? ›Repetition Operator(*) on List Items. Python List also includes the * operator, which allows you to create a new list with the elements repeated the specified number of times.
What are the 4 types of list? ›- Ordered List or Numbered List (ol)
- Unordered List or Bulleted List (ul)
- Description List or Definition List (dl)
- Bulleted lists, when list elements could appear in any order.
- Numbered lists, when list elements must appear in a particular order.
Punctuation for Lists of Items Within a Sentence
Use commas after each item in a list of three or more items. Nurses monitor a patient's vital signs including temperature, blood pressure, respiratory rate, and pulse. Use semi-colons after each item in a list if one or more items already includes a comma.
A list is any information displayed or organized in a logical or linear formation. Below is an example of a numerical list, often used to show several steps that need to be performed to accomplish something.
What are the different methods in list? ›| Method | Description |
|---|---|
| count() | Returns the number of elements with the specified value |
| extend() | Add the elements of a list (or any iterable), to the end of the current list |
| index() | Returns the index of the first element with the specified value |
| insert() | Adds an element at the specified position |
Also called a series, a catalog, an inventory, and (in classical rhetoric) enumeratio. Lists are often used in works of fiction and creative nonfiction (including essays) to evoke a sense of place or character.
How many times a value appears in a list Python? ›1) Using count() method
count() is the in-built function by which python count occurrences in list. It is the easiest among all other methods used to count the occurrence. Count() methods take one argument, i.e., the element for which the number of occurrences is to be counted.
The Python count() method calculates how many times a particular element appears in a list or a string. count() accepts one argument: the value for which you want to search in the list. The count() method is appended to the end of a list or a string object.
How to count the number of repeated elements in a list in Python? ›
Given a list in Python and a number x, count the number of occurrences of x in the given list. Examples: Input: lst = [15, 6, 7, 10, 12, 20, 10, 28, 10], x = 10 Output: 3 Explanation: 10 appears three times in given list.
How do you flatten a list in Python? ›- List_2D = [[1,2,3],[4,5,6],[7,8,9]] #List to be flattened. List_flat = [] for i in range(len(List_2D)): #Traversing through the main list. ...
- import functools. import operator. ...
- import itertools. List_2D = [[1,2,3],[4,5,6],[7,8,9]] #List to be flattened.
PYTHON List Count() method: The count() method in Python returns the number of elements that appear in the specified list. This method takes a single argument as input. It iterates the list and counts the number of instances that match it.
How do you find the index of a value in a list in Python? ›- my_list is the name of the list you are searching through.
- . index() is the search method which takes three parameters. ...
- item is the required parameter. ...
- start is the first optional parameter. ...
- end the second optional parameter.
The LIST command displays information about a program such as values of specified variables, structures, arrays, registers, statement numbers, frequency information, and the flow of program execution.
What do lists do in coding? ›A list is a sequence of several variables, grouped together under a single name. Instead of writing a program with many variables x0 , x1 , x2 , … you can define a single variable x and access its members x[0] , x[1] , x[2] , etc.
What does a list do to the reader? ›Lists allow you to emphasize important ideas. They also increase the readability of text by simplifying long sentences or paragraphs and adding aesthetic passive space to make reading more pleasant. However, using the wrong kind of list or poorly formatting a list can create confusion rather than enhance readability.
Why do people use lists? ›By keeping such a list, you make sure that your tasks are written down all in one place so you don't forget anything important. And by prioritizing tasks, you plan the order in which you'll do them, so that you can tell what needs your immediate attention, and what you can leave until later.
Which command is used to list? ›The ls command is used to list files. "ls" on its own lists all files in the current directory except for hidden files.
Which command displays a list? ›The dir command displays a list of files and subdirectories in a directory. With the /S option, it recurses subdirectories and lists their contents as well.
What are command lists? ›
A command list is a sequence of GPU commands that can be recorded and played back. A command list may improve performance by reducing the amount of overhead generated by the runtime.
Can you put a variable in a list? ›Since a list can contain any Python variables, it can even contain other lists.
Why is it important not to do lists? ›To-do lists can work for you, but if you are not using them effectively, they can actually leave you feeling more disillusioned and stressed than you did before. Think of a filing system: the concept is good, but if you merely file papers away with no structure or system, the filing system will have an adverse effect.
How do you make lists easier to read? ›Use a consistent pattern for list items. Write items in a list so they follow a consistent pattern. The pattern is made up by the number of words you use and grammatical structure. If items follow a consistent pattern, it makes a list easier to scan and understand.
What is a list example? ›What is a List? A list is an ordered data structure with elements separated by a comma and enclosed within square brackets. For example, list1 and list2 shown below contains a single type of data. Here, list1 has integers while list2 has strings.
What is the correct way to write a list? ›You should create bulleted lists starting with a lead-in then using between 4-10 list items. For most list items, you will use bullet points. A bulleted list delineates items in which the order doesn't matter, such as items on a grocery list or types of software.
Do successful people use to do lists? ›But as it turns out, it's not a to do list at all. Successful people do not work from a list of everything they need to do. Successful people use a calendar to break their days into 15-minute intervals. The world's most successful and productive people schedule everything.
Why do I obsessively make lists? ›People with OCD often fear they will forget something important, so they may make excessive lists to remind them to do daily routine activities (i.e. brush teeth, make breakfast, etc.) However, research has shown that people with OCD do not have memory problems, so the lists are actually unnecessary.
What kind of person makes lists? ›ENFJs enjoy making lists in order to keep everything organized and together. They have so much going on in their lives and they want to be sure to keep everything maintained properly. Without lists the ENFJ can feel like they are missing or forgetting something important.