insert() adds the element at the particular index of the list that you choose.,You can add elements to an empty list using the methods append() and insert():,💡 Tip: We commonly use append() to add the first element to an empty list, but you can also add this element calling the insert() method with index 0:,In the example below, we create an empty list and assign it to the variable num. Then, using a for loop, we add a sequence of elements (integers) to the list that was initially empty:
For example:
num = []
The empty list will have length 0, as you can see right here:
>>> num = [] >>> len(num) 0
Empty lists are falsy values, which means that they evaluate to False in a boolean context:
>>> num = [] >>> bool(num) False
The output of this code is:
This list is empty
In the example below, we create an empty list and assign it to the variable num. Then, using a for loop, we add a sequence of elements (integers) to the list that was initially empty:
>>> num = [] >>> for i in range(3, 15, 2): num.append(i)
July 23, 2021July 23, 2021
Use Python List append() Method to append to an empty list. This method will append elements (object) to the end of an empty list.
list.append("obj")You can also use the + operator to concatenate a list of elements to an empty list.
list = list + ["obj"]a_list = []
a_list.append("New item")
print(a_list)append actually changes the list. Also, it takes an item, not a list. Hence, all you need is
for i in range(n):
list1.append(i)I assume your actual use is more complicated, but you may be able to use a list comprehension, which is more pythonic for this:
list1 = [i for i in range(n) ]
append returns None, so at the second iteration you are calling method append of NoneType. Just remove the assignment:
for i in range(0, n):
list1.append([i])I personally prefer the + operator than append:
for i in range(0, n):
list1 += [
[i]
]Note that you also can use insert in order to put number into the required position within list:
initList = [1, 2, 3, 4, 5] initList.insert(2, 10) # insert(pos, val) => initList = [1, 2, 10, 3, 4, 5]
In Python, an empty list can be created by just writing square brackets i.e. []. If no arguments are provided in the square brackets [], then it returns an empty list i.e. ,Inside the constructor it checks if an iterable sequence is passed, if no then only it creates an empty list.,We can create an empty list in python either by using [] or list(), but the main difference between these two approaches is speed. [] is way faster than list() because,,There are two ways to create an empty list in python i.e. using [] or list(). Let’s check out both of them one by one,
In Python, an empty list can be created by just writing square brackets i.e. []. If no arguments are provided in the square brackets [], then it returns an empty list i.e.
# Creating empty List using[]
sample_list = []
print('Sample List: ', sample_list)Sample List: []
Python’s list class provide a constructor,
list([iterable])We will use the range() function like the previous example to generate an iterable sequence of numbers from 0 to 9. But instead of calling append() function, we will use List comprehension to iterate over the sequence and add each number at the end of the empty list. Let’s see how to do that,
# Append 10 numbers in an empty list from number 0 to 9 sample_list = [i for i in range(10) ]
Python provides a function insert() i.e.
list.insert(index, item)
Last Updated : 16 Aug, 2022
The original list is: [5, 6, [], 3, [], [], 9 ] List after empty list removal: [5, 6, 3, 9]
5.1.3. List Comprehensions,5.7. More on Conditions,5.1.2. Using Lists as Queues,5.1.1. Using Lists as Stacks
>>> fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana'] >>>
fruits.count('apple')
2
>>>
fruits.count('tangerine')
0
>>>
fruits.index('banana')
3
>>>
fruits.index('banana', 4) # Find next banana starting a position 4
6
>>>
fruits.reverse() >>>
fruits['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange'] >>>
fruits.append('grape') >>>
fruits['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape'] >>>
fruits.sort() >>>
fruits['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear'] >>>
fruits.pop()
'pear'>>> stack = [3, 4, 5] >>> stack.append(6) >>> stack.append(7) >>> stack[3, 4, 5, 6, 7] >>> stack.pop() 7 >>> stack[3, 4, 5, 6] >>> stack.pop() 6 >>> stack.pop() 5 >>> stack[3, 4]
>>> from collections
import deque
>>>
queue = deque(["Eric", "John", "Michael"]) >>>
queue.append("Terry") # Terry arrives >>>
queue.append("Graham") # Graham arrives >>>
queue.popleft() # The first to arrive now leaves 'Eric' >>>
queue.popleft() # The second to arrive now leaves 'John' >>>
queue # Remaining queue in order of arrival
deque(['Michael', 'Terry', 'Graham'])>>> squares = [] >>> for x in range(10): ...squares.append(x ** 2) ... >>> squares[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
squares = list(map(lambda x: x ** 2, range(10)))
squares = [x ** 2 for x in range(10) ]