List Flashcards
Complete List with List funtions
Question: What is a list in Python?
Answer: A list is an ordered collection of elements enclosed in square brackets [ ] and separated by commas. Lists are mutable and can store multiple data types.
Question: What are the key properties of a list in Python?
Lists are ordered sequences.
Lists can store multiple values in a single object.
Lists are mutable (modifiable).
Lists can contain heterogeneous elements (different data types).
Elements are enclosed in square brackets [ ] and separated by commas.
Question: How do you create a list in Python?
L = [1, 5, 7, 2] # List with integers
L = [1.5, 2, “Hello”, ‘S’] # List with mixed data types
L = list(“Hello”) # Creating a list from a string
L = [] # Empty list
L = list() # Another way to create an empty list
Question: What is a sequence in Python?
Answer: A sequence is a positional ordered collection of elements that can be accessed using indexing. Examples include List, Tuple, and String.
Question: What is indexing in a list?
Answer: Indexing refers to accessing elements in a list using their position.
Positive Indexing starts from 0.
Negative Indexing starts from -1 (last element).
Example:L = [5, 8, 6, 1, 9]
print(L[0]) # Output: 5
print(L[-1]) # Output: 9
Question: What is slicing in lists?
list[start:stop:step]
L = [5, 8, 6, 1, 9]
print(L[1:4]) # Output: [8, 6, 1]
print(L[::-1]) # Reverse list: [9, 1, 6, 8, 5]
Question: How do you concatenate two lists?
L1 = [1, 2, 3]
L2 = [‘a’, ‘b’, ‘c’]
print(L1 + L2) # Output: [1, 2, 3, ‘a’, ‘b’, ‘c’]
Question: How do you repeat a list multiple times?
L = [1, 2, 3] * 3
print(L) # Output: [1, 2, 3, 1, 2, 3, 1, 2, 3]
Question: What are membership operators in lists?
Answer:
in checks if an element exists in a list.
not in checks if an element does not exist in a list.
L = [5, “India”, 8, 6, 1]
print(5 in L) # Output: True
print(9 not in L) # Output: True
1: len():
It returns the total number of elements in the list i.e. length of the list.
For ex:
»> L = [8, 6, 3, 9, 1]
»> len(L)
5
2: list()
list() is a function used to convert an iterable into a list.
For Ex:
»> S=”Python”
»> L=list(S)
»> L
[‘P’, ‘y’, ‘t’, ‘h’, ‘o’, ‘n’]
3: append()
appends an element at the end of the list.
list.append(item)
append() adds a single element to the end of a list.
The length of the list increases by one.
The method doesn’t return any value
»> L = [4,5,9,2,6]
»> L.append(1)
»> L
[4, 5, 9, 2, 6, 1]
A list is an object. If we append another list onto a list, the parameter list will be a single object at the end
of the list.
»> L1=[1,2,3]
»> L2=[4,5,6]
»> L1.append(L2)
»> L1
[1, 2, 3, [4, 5, 6]]
4: extend()
extend() is a method of list, which is used to merge two lists.
extend() iterates over its argument and adds each element at the end of the list.
list.extend(iterable)
Argument of extend() method is any iterable (list, string, set, tuple etc.)
The length of the list increases by a number of elements in its argument.
The method doesn’t return any value
»> L1=[1,2,3]
»> L2=[4,5,6]
»> L1.extend(L2)
»> L1
[1, 2, 3, 4, 5, 6]
A string is iterable, so if you extend a list with a string, you’ll append each character as you iterate over
the string.
»> L1=[1,2,3]
»> S=”Python”
»> L1.extend(S)
»> L1
[1, 2, 3, ‘P’, ‘y’, ‘t’, ‘h’, ‘o’, ‘n’]
5: insert()
append() and extend() method is used to add an element and elements of an iterable object respectively at
the end of the list. If we want to add an element at any index then we can use insert() method of list.
Syntax: list_name.insert(index, element)
»> L=[1,2,3]
Insert element 8 at index 1 i.e. at 2nd position
»> L.insert(1,8)
»> L
[1, 8, 2, 3]
6: count()
count() method returns how many times a given element occurs in a List i.e. it returns the frequency of an
element in the list.
Syntax: list_name.count(element)
»> L = [1, 2, 8, 9, 2, 6, 2]
»> L
[1, 2, 8, 9, 2, 6, 2]
»> L.count(2)
3
7: index()
index() is a method of the list, which returns the index of the first occurrence of the element.
Syntax: list_name.index(element, start, end)
element – The element whose index for first occurrence is to be returned.
start (Optional) – The index from where the search begins. Start is included.
end (Optional) – The index from where the search ends. End is excluded.
»> L = [5, 8, 9, 6, 1, 8]
»> L.index(8)
1
»> L.index(8,2)
5
»> L.index(8,2,6)
5
»> L.index(8,2,5)
ValueError: 8 is not in list
»> L.index(8,2,7)
5
8: remove()
remove() method of list is used to delete the first occurrence of the given element. If the given element is
not exist in the list then it will give the ValueError
Syntax: list_name.remove(element)
»> L
[5, 8, 9, 6, 1, 8]
»> L.remove(8)
»> L
[5, 9, 6, 1, 8]
»> L.remove(4)
ValueError: list.remove(x): x not in list
9: pop()
Syntax: list_name.pop(index)
Index is optional. If index is not given, pop() method of list is used to remove and return the last element
of the list, otherwise remove and return the element of the given index. If Index is out of range then it
gives IndexError.
»> L = [5, 8, 9, 6, 1]
»> L
[5, 8, 9, 6, 1]
#remove the last element from the list
»> L.pop()
100
1
»> L
[5, 8, 9, 6]
#remove the element from the list whose index is 1
»> L.pop(1)
8
»> L
[5, 9, 6]
»> L.pop(4)
IndexError: pop index out of range
10: reverse()
reverse() method of the list used to reverse the order of the elements of the list
Syntax: list_name.reverse()
»> L = [5, 8, 9, 6, 1]
»> L
[5, 8, 9, 6, 1]
»> L.reverse()
»> L
[1, 6, 9, 8, 5]
11: sort()
sort() method can be used to sort List in ascending, descending, or user-defined order. It sort the existing
list.
Syntax: List_name.sort(reverse=True/False)
»> L = [5, 8, 9, 6, 1]
»> L
[5, 8, 9, 6, 1]
#sort the elements of the list in ascending order
»> L.sort()
»> L
[1, 5, 6, 8, 9]
#sort the elements of the list in descending order
»> L.sort(reverse=True)
»> L
[9, 8, 6, 5, 1]
12: sorted()
sorted() is a function of list. sorted() function returns a sorted list in ascending order by default. It does not
sort or change the existing list.
101
»> L = [5, 8, 9, 6, 1]
»> L
[5, 8, 9, 6, 1]
»> sorted(L)
[1, 5, 6, 8, 9]
»> L
[5, 8, 9, 6, 1]
#Create a list which contains the element of another list in descending order.
»> L1=sorted(L, reverse=True)
»> L1
[9, 8, 6, 5, 1]
13: min()
If the elements of the list are string then min() returns the minimum element based on the ASCII values.
> > > L = [5, 8, 1, 6, 9]
min(L)
1
> > > > > > L=[‘a’,’D’,’c’]
min(L)
‘D’
14: max()
If the elements of the list are string then max() returns the maximum element based on the ASCII
max() function of the list is used to find the maximum element from the list.
»> L = [5, 8, 1, 6, 9]
»> max(L)
9
values.
> > > > > > L=[‘a’,’D’,’c’]
max(L)
‘c’
15: sum()
sum() is a function of list, which returns the sum of all elements of the list.
»> L = [5, 8, 9, 6, 1]
»> sum(L)
29
Nested List:
A list within another list is called the nested list i.e. list of list.
»> L = [1, [2, 3, 4], ‘Python’, 3.5]
»> L[1]
[2, 3, 4]
»> L[1][0]
2
»> L[2]
‘Python’
»> L[2][2]
‘t’
Write a program in Python to find the maximum and minimum number from the
given List.
L=[]
c=’y’
while c==’y’ or c==’Y’:
a=int(input(“Enter an integer number to append in the list: “))
L.append(a)
c=input(“Do you want to add more elements in the list (Y/N): “)
print(“List is: \n”, L)
print(“Minimum(Smallest) number of the list = “,min(L))
print(“Maximum(Largest) number of the list = “,max(L))
Write a program in Python to find the mean of numeric values stored in the given List.
L=eval(input(“Enter a list: “))
print(“List is: \n”, L)
NL=[ ]
for i in L:
if isinstance(i, (int, float)) ==True:
NL.append(i)
print(“Numeric List is: \n”, NL)
mean=sum(NL)/len(NL)
print(“Mean of the numeric values of the list = “,mean)
Write a program in Python to count the frequency of all elements of a list
L= [10, 20, 30, 20, 40, 30, 20, 50]
print(“List is: “,L)
Uni= []
Freq= []
for i in L:
if i in Uni:
index=Uni.index(i)
Freq[index]+= 1
else:
Uni.append(i)
Freq.append(1)
for i in range(len(Uni)):
print(Uni[i],”:”,Freq[i])
