Question 1

Question 1Why are dictionaries called mutable types?

Accepted Answer

Dictionaries can be changed by adding new key-value pairs and by deleting or changing the existing ones. Hence they are called as mutable types.For example:d = {"a" : 1 , "b" : 2}
d["c"] = 3 
d["b"] = 4
del d["a"]
print(d)Output{'b': 4, 'c': 3} 
dict["c"] = 3 adds a new key-value pair to dict.dict["b"] = 4 changes existing key-value pair in dict.del dict["a"] removes the key-value pair "a" : 1

Question 2

Question 2What are different ways of creating dictionaries?

Accepted Answer

The different ways of creating dictionaries in Python are:1. By using curly brackets and separating key-value pairs with commas as per the syntax below: = {:, :...} For example: d = {'a': 1, 'b': 2, 'c': 3} 2. By using dictionary constructor dict(). There are multiple ways to provide keys and values to dict() constructor:i. Specifying key:value pairs as keyword arguments to dict() function:For example:Employee = dict(name = 'john' , salary = 1000, age = 24) print(Employee)Output{'name': 'john', 'salary': 1000, 'age': 24} ii. Specifying comma separated key:value pairs:Key:value pairs are enclosed in curly braces in this format.For example:Employee = dict({'name': 'john', 'salary': 1000, 'age': 24})Output{'name': 'john', 'salary': 1000, 'age': 24} iii. Specifying keys and its corresponding values separately:Keys and Values are enclosed separately in parentheses and are given as arguments to zip() function.For example:Employee = dict(zip(('name','salary','age'),('John',10000,24))) Output{'name': 'John', 'salary': 10000, 'age': 24} iv. Specifying key:value pairs separately in form of sequences:One list or tuple that contains lists/tuples of individual key:value pairs is passed as an argument to dict().For example:Employee = dict([['name','John'],['salary',10000],['age',24]]) print(Employee)Output{'name': 'John', 'salary': 10000, 'age': 24} 3. By using fromkeys() function:fromkeys() function is used to create a new dictionary from a sequence containing all the keys and a common value, which will be assigned to all the keys.For example:x = ('list', 'set', 'dictionary') y = 'mutable' my_dict = dict.fromkeys(x, y) print(my_dict)Output{'list': 'mutable', 'set': 'mutable', 'dictionary': 'mutable'}

Question 3

Question 3What values can we have in a dictionary?

Accepted Answer

A dictionary can have values of all data types i.e., integers, floats, strings, booleans, sequences and collections, etc. For example:d = {1:'a' , 2: 2 , 3: True , 4: 3.5 , 5: "python",(1,2,3) : 4}

Question 4

Question 9How do you add key:value pairs to an existing dictionary?

Accepted Answer

There are three ways by which new key:value pairs can be added to an existing dictionary:1. By using assignment as per the following syntax:[] = For example:d = {1 : 'a' , 2 : 'b'} d[3] = 'c' print(d)Output{1: 'a', 2: 'b', 3: 'c'}2. By using update() method:update() method merges key:value pairs from new dictionary into the original dictionary adding or replacing as needed. The syntax to use this method is:.update() For example:d = {1 : 'a' , 2 : 'b'} d.update({3 : 'c'}) print(d)Output{1: 'a', 2: 'b', 3: 'c'}3. Using setdefault() method:It inserts a new key:value pair only if the key doesn't already exist. If the key already exists, it returns the current value of the key. The syntax to use this method is:.setdefault(,) For example:d = {1 : 'a' , 2 : 'b'} d.setdefault(3,'c') print(d)Output{1: 'a', 2: 'b', 3: 'c'}

Question 5

Question 10Can you remove key:value pairs from a dictionary and if so, how?

Accepted Answer

Yes, key:value pairs can be removed from a dictionary. The different methods to remove key:value pairs are given below:1. By using del command:It is used to delete an item with the specified key name. The syntax for doing so is as given below:del []For example:dict = {'list': 'mutable', 'tuple': 'immutable', 'dictionary': 'mutable'} del dict["tuple"] print(dict)Output{'list': 'mutable', 'dictionary': 'mutable'} 2. By using pop() method:This method removes and returns the dicitionary element associated to the passed key. It is used as per the syntax:.pop(key, )For example:dict = {'list': 'mutable', 'tuple': 'immutable', 'dictionary': 'mutable'} dict.pop("tuple") print(dict)Output{'list': 'mutable', 'dictionary': 'mutable'} 3. popitem() method:This method removes and returns the last inserted item in the dictionary. It is used as per the syntax:.popitem()For example:dict = {'list': 'mutable', 'tuple': 'immutable', 'dictionary': 'mutable'} dict.popitem() print(dict)Output{'list': 'mutable', 'tuple': 'immutable'} Here, the last element of dict was 'dictionary': 'mutable' which gets removed by function popitem().

Question 6

Question 8Which of the following can be used to delete item(s) from a dictionary?del statementpop( )popitem( )all of these

Accepted Answer

all of theseReason —del keyword is used to delete an item with the specified key name.For example:d =	{'list': 'mutable', 'tuple': 'immutable', 'dictionary': 'mutable'} 
del dict["tuple"]
print(d)Output{'list': 'mutable', 'dictionary': 'mutable'} 
del keyword deletes the key "tuple" and it's corresponding value.pop() method removes the item with the specified key name: For example:d =	{'list': 'mutable', 'tuple': 'immutable', 'dictionary': 'mutable'} 
d.pop("tuple")
print(d)Output{'list': 'mutable', 'dictionary': 'mutable'} 
The key named "tuple" is popped out. Hence dictionary d has only two key-value pairs.popitem() method removes the last inserted item of dictionary.For example:d =	{'list': 'mutable', 'tuple': 'immutable', 'dictionary': 'mutable'} 
d.popitem()
print(d)Output{'list': 'mutable', 'tuple': 'immutable'} 
Here, the last element of d was 'dictionary': 'mutable' which gets removed by function popitem().

Question 7

Question 23What will be the output of following Python code?d1 = {"a":10,"b":2,"c":3}
str1=""
for i in d1:
    str1 = str1 + str(d1[i]) + " " 
    str2 = str1[:-1]
print(str2[::-1])3, 23, 2, 103, 2, 01Error

Accepted Answer

3, 2, 01Reason — d1 is a dictionary containing three elements. str1 is initialized to an empty string.Inside the for loop, the values of dictionary d1 are getting concatenated to str1 as a string. The statement str2 = str1[:-1] takes a slice of str1 from start to end and assigns to str2. So effectively, this statement is assigning str1 to str2.The detailed execution of the for loop is shown in the table below:id1[i]str(d1[i])str1str2"a"10"10""10 ""10""b"2"2""10 2 ""10 2""c"3"3""10 2 3 ""10 2 3"Now the expression str2[::-1] will reverse the string "10 2 3" to '3 2 01'

Question 8

Question 24Running the code sorted(my_dictionary, reverse = True) on a dictionary named my_dictionary will return results sorted in what order?Ascending order (A-Z), by keyAscending order (A-Z), by valueDescending order (Z-A), by keyDescending order (Z-A), by value

Accepted Answer

Descending order (Z-A), by keyReason — The sorted() function returns a sorted list of dictionary keys. By default, the sort order is ascending. To sort the keys in descending order, the reverse parameter must be set to true as an optional argument (sorted(my_dictionary, reverse = True)).

Question 9

Question 5Can you change the order of dictionary's contents, i.e., can you sort the contents of a dictionary ?

Accepted Answer

No, the contents of a dictionary cannot be sorted in place like that of a list. However, we can indirectly sort the keys and values of a dictionary by using sorted() function:sorted(dictionary.keys())sorted(dictionary.values())sorted(dictionary)sorted(dictionary.items())For example:>>> d = {"def" : 2 ,"abc" : 1, "mno" : 3}
>>> sorted(d.keys())
>>> sorted(d.values())
>>> sorted(d)
>>> sorted(d.items())Output['abc', 'def', 'mno']  
[1, 2, 3]  
['abc', 'def', 'mno']  
[('abc', 1), ('def', 2), ('mno', 3)]

Question 10

Question 15Can you use sum( ) for calculating the sum of the values of a dictionary ?

Accepted Answer

It is not possible to use the sum( ) function to calculate the sum of values in a dictionary, as sum( ) function only works with the keys, and only when the keys are homogenous and addition compatible.We can calculate the sum of the values of a dictionary with the help of values( ) and sum( ) functions as shown in the example below:d = {"abc" : 1 ,"def" : 2 , "mno" : 3}
sum(d.values())

Question 11

Question 17What is the use of copy( ) function ?

Accepted Answer

The copy() function is used to create a shallow copy of a dictionary where only a copy of keys is created and the values referenced are shared by the two copies.For example:original_d = {1:'a', 2:'b'} 
new_d = original_d.copy()
print(new_d)Output{1: 'a', 2: 'b'}Here, original_d and new_d are two isolated objects, but their contents still share the same reference i.e ('a','b')

Question 12

Question 18Discuss the working of copy( ) if(i) the values are of immutable types,(ii) the values are of mutable types.

Accepted Answer

(i) the values are of immutable typesIf the values are of immutable types then any changes made in the copy created with copy( ) will not be reflected in the original dictionary.For example:d1 = {1:'Neha' , 2: 'Saima' , 3: 'Avnit' , 4: 'Ana'}
d2 = d1.copy()
d2[5] = 'Taru'
print(d2)
print(d1)Output{1: 'Neha', 2: 'Saima', 3: 'Avnit', 4: 'Ana', 5: 'Taru'} 
{1: 'Neha', 2: 'Saima', 3: 'Avnit', 4: 'Ana'} 
(ii) the values are of mutable typesIf the values are of mutable types then any changes made in the copy created with copy() will be reflected in the original dictionary.For example:d1 = {1:[1,2,3] , 2: [3,4,5]}
d2 = d1.copy()
d2[1].append(4)
print(d2)
print(d1)Output{1: [1, 2, 3, 4], 2: [3, 4, 5]}
{1: [1, 2, 3, 4], 2: [3, 4, 5]}

Question 13

Question 9(c)Predict the output:text = "abracadabraaabbccrr" 
counts = {}
ct = 0
lst = []
for word in text:
  if word not in lst:
    lst.append(word)
    counts[word] = 0
  ct = ct + 1
  counts[word] = counts[word] + 1 
print(counts)
print(lst)

Accepted Answer

Output{'a': 7, 'b': 4, 'r': 4, 'c': 3, 'd': 1} 
['a', 'b', 'r', 'c', 'd']
ExplanationThis python program counts the frequency of each character in a string. Here is a step-by-step explanation of the program:Initialize the variablesThe text variable stores the input string "abracadabraaabbccrr".The counts variable is a dictionary that stores the frequency of each character in the string.The ct variable is a counter that keeps track of the total number of characters in the string.The lst variable is a list that stores the unique characters in the string.Loop through each character word in the text stringIf the character has not been seen before, it is added to the lst list and a new key is added to the counts dictionary with a value of 0.The ct variable is incremented by 1.The value of the character's key in the counts dictionary is incremented by 1. This value keeps a count of the number of times this character has appeared in the string so far.Finally, the counts dictionary and the lst list are printed to the console. The counts dictionary displays the frequency of each character in the string, and the lst list displays the unique characters in the string.

Question 14

Question 9(d)Predict the output:list1 = [2, 3, 3, 2, 5,3, 2, 5, 1,1] 
counts = {}
ct = 0
lst = []
for num in list1:
  if num not in lst:
    lst.append(num)
    counts[num] = 0
  ct = ct+1
  counts[num] = counts[num]+1 
print(counts)
for key in counts.keys():
  counts[key] = key * counts[key] 
print(counts)

Accepted Answer

Output{2: 3, 3: 3, 5: 2, 1: 2} 
{2: 6, 3: 9, 5: 10, 1: 2} 
ExplanationThis python program counts the frequency of each number in a list and then multiplies each frequency by its corresponding number. Here is a step-by-step explanation of the program:Initialize the variablesThe list1 variable stores the input list [2, 3, 3, 2, 5, 3, 2, 5, 1, 1].The counts variable is a dictionary that stores the frequency of each number in the list.The ct variable is a counter that keeps track of the total number of numbers in the list.The lst variable is a list that stores the unique numbers in the list.Loop through each number num in the list1If the number has not been seen before, it is added to the lst list and a new key is added to the counts dictionary with a value of 0.The ct variable is incremented by 1.The value of the number's key in the counts dictionary is incremented by 1.The counts dictionary is printed to the console after the first loop, displaying the frequency of each number in the list.Another loop is executed through the keys in the counts dictionary. For each key, its corresponding value is multiplied by the key and the new value is assigned back to the key in the counts dictionary.The final counts dictionary is printed to the console, showing the frequency of each number multiplied by the number itself.

Question 15

Question 10Create a dictionary 'ODD' of odd numbers between 1 and 10, where the key is the decimal number and the value is the corresponding number in words.Perform the following operations on this dictionary :Display the keysDisplay the valuesDisplay the itemsFind the length of the dictionaryCheck if 7 is present or notCheck if 2 is present or notRetrieve the value corresponding to the key 9Delete the item from the dictionary corresponding to the key 9

Accepted Answer

>>> ODD = { 1 : 'One', 3 : 'Three', 5 : 'Five', 7 : 'Seven', 9 : 'Nine' }

>>> ODD.keys()
# (1) Display the keys

>>> ODD.values()
# (2) Display the values

>>> ODD.items()
# (3) Display the items

>>> len(ODD)
# (4) Find the length of the dictionary

>>> 7 in ODD
# (5) Check if 7 is present or not

>>> 2 in ODD
# (6) Check if 2 is present or not

>>> ODD[9]
# (7) Retrieve the value corresponding to the key 9

>>> del ODD[9]
# (8) Delete the item from the dictionary corresponding to the key 9Outputdict_keys([1, 3, 5, 7, 9]) 
dict_values(['One', 'Three', 'Five', 'Seven', 'Nine'])  
dict_items([(1, 'One'), (3, 'Three'), (5, 'Five'), (7, 'Seven'), (9, 'Nine')]) 
5
True
False
Nine

Question 16

Question 11(a)Find the errors:text = "abracadbra"
counts = {}
for word in text :
  counts[word] = counts[word] + 1

Accepted Answer

OutputKeyError: 'a' 
ExplanationThe line counts[word] = counts[word] + 1 will cause a KeyError because we are trying to access a key word of an empty dictionary. As the key is not present in dictionary counts, hence a KeyError is generated.

Question 17

Question 12(a)Predict the output:fruit = {}
L1 = ['Apple', 'banana', 'apple'] 
for index in L1 :
  if index in fruit: 
    fruit[index] += 1
  else :
    fruit[index] = 1
print(len(fruit))
print(fruit)

Accepted Answer

Output3
{'Apple': 1, 'banana': 1, 'apple': 1} 
ExplanationThis python program counts the frequency of each fruit in a list and outputs the number of unique fruits and their frequency. The program does not account for the case sensitivity of the fruit names so "Apple" and "apple" are counted as separate fruits. Here is a step-by-step explanation of the program:Initialize the variablesThe fruit variable is a dictionary that stores the frequency of each fruit.The L1 variable stores the input list ['Apple', 'banana', 'apple'].Loop through each fruit index in the list L1If the fruit already exists as a key in the fruit dictionary, its value is incremented by 1.If the fruit is not in the fruit dictionary, a new key is added with a value of 1.The length of the fruit dictionary is printed to the console, indicating the number of unique fruits.The fruit dictionary is printed to the console, showing the frequency of each fruit.

Question 18

Question 13(b)Predict the outputa = {'a':1, 'b':2, 'c':3}
print(a['a','b'])

Accepted Answer

OutputKeyError: ('a', 'b')  
Explanationa is a dictionary containing three key-value pairs.a['a','b'] will throw an error since given key ('a','b') is not present in dictionary a.

Question 19

Question 14Find the error/output. Consider below given two sets of codes. Which one will produce an error? Also, predict the output produced by the correct code.(a)box = {}
jars = {'Jam' :4}
crates = {}	
box['biscuit'] = 1	
box['cake'] = 3	
crates['box'] = box	
crates['jars'] = jars	
print(len(crates[box]))(b)box = {}
jars = {'Jam' :4}
crates = {}	
box['biscuit'] = 1	
box['cake'] = 3	
crates['box'] = box	
crates['jars'] = jars	
print(len(crates['box']))

Accepted Answer

The code given in set (a) will produce an error.In the line print(len(crates[box])), we are trying to print the value from dictionary crates by taking mutable type dictionary i.e box as key — crates[box]. The keys of the dictionary cannot be of mutable type, hence this code produces this error.The code given in set (b) is correct. Its output is as shown below:Output of set (b) code2
Explanationcrates['box'] will return the value of key 'box' from dictionary crates i.e, box. box is itself a dictionary containing two key-value pairs i.e:{'biscuit': 1, 'cake': 3}Therefore, the expression len(crates['box']) becomes len(box) which will return the length of box i.e., 2.

Question 20

Question 15Predict the output :dct = {}
dct[1] = 1
dct ['1'] = 2 
dct[1.0] = 4 
sum = 0
for k in dct: 
  print(k, sum)
  sum += dct[k]
print(sum)

Accepted Answer

Output1 0
1 4
6
ExplanationThis python program computes the sum of values of items in the dictionary. It also demonstrates that dictionaries in Python can have both integer and string keys, but the keys must be unique.The keys 1 and '1' will be treated as two different keys as the former is a number and the latter is a string. But the keys 1 and 1.0 are considered the same as both represent number 1.Here is a step-by-step explanation of the program:1. The dct dictionary is created and initialized with two key-value pairs, dct[1] = 1 and dct['1'] = 2.2. After that, dct[1.0] = 4 updates the value of key 1 to 4 as the keys 1 and 1.0 are considered the same. At this point, dct = {1: 4, '1': 2}.3. Loop through each key k in dct. Below table shows the loop iterations:kdct[k]sumIteration140 + 4 = 4Iteration 1'1'24 + 2 = 6Iteration 24. The final value of the sum variable is printed to the console.

Dictionaries

Checkpoint 13.1

Multiple Choice Questions

Type A : Short Answer Questions/Conceptual Questions

Type B: Application Based Questions

Type C: Programming Practice/Knowledge based Questions