A Python dictionary is a powerful data structure that stores key-value pairs. It's versatile, efficient, and widely used in Python programming for its simplicity and flexibility. Let's delve into a comprehensive description of Python dictionaries, covering their definition, syntax, operations, methods, use cases, and more. ### Definition: A dictionary in Python is an unordered collection of items. Each item is a pair of a key and its corresponding value. Unlike sequences such as lists or tuples, dictionaries are indexed by keys, not by a range of numbers. ### Syntax: Dictionaries are defined using curly braces `{}`. Each item in a dictionary is written as a key-value pair separated by a colon `:`. Keys are unique within a dictionary, while values can be of any data type, including integers, strings, lists, tuples, other dictionaries, or even functions. Example: ```python my_dict = {'name': 'John', 'age': 30, 'city': 'New York'} ``` ### Operations: 1. **Accessing Values:** You can access the value associated with a key using square brackets `[]`. Example: ```python print(my_dict['name']) # Output: John ``` 2. **Updating Values:** You can update the value associated with a key by assigning a new value to that key. Example: ```python my_dict['age'] = 31 ``` 3. **Adding New Items:** You can add new key-value pairs to a dictionary by assigning a value to a new key. Example: ```python my_dict['gender'] = 'Male' ``` 4. **Removing Items:** You can remove key-value pairs from a dictionary using the `del` keyword or the `pop()` method. Example: ```python del my_dict['city'] my_dict.pop('age') ``` ### Methods: Python provides several built-in methods to perform various operations on dictionaries: 1. `clear()`: Removes all items from the dictionary. 2. `copy()`: Returns a shallow copy of the dictionary. 3. `get(key[, default])`: Returns the value associated with the specified key, or a default value if the key is not found. 4. `items()`: Returns a view object that displays a list of a dictionary's key-value pairs. 5. `keys()`: Returns a view object that displays a list of the dictionary's keys. 6. `values()`: Returns a view object that displays a list of the dictionary's values. 7. `pop(key[, default])`: Removes the item with the specified key and returns its value. If the key is not found, it returns the default value. 8. `popitem()`: Removes and returns the last inserted key-value pair. 9. `update()`: Updates the dictionary with the key-value pairs from another dictionary or an iterable of key-value pairs. ### Use Cases: 1. **Storing Data:** Dictionaries are commonly used to store data in a structured format, especially when the data has associated labels or categories. 2. **Configuration Settings:** Dictionaries are useful for storing configuration settings in Python applications. 3. **Caching:** Dictionaries can be used to cache the results of expensive function calls for improved performance.

1. Dictionaries
Week 8
Course: Programming in Python
CEC-Swayam/EMRC Dibrugarh University

2. Dictionaries
Dictionary is a built-in Python Data
Structure and are used to store data
values in key:value pairs. Each key is
separated from its value by a colon ( : ).
Dictionaries are not indexed by a
sequence of numbers but indexed
based on keys

3. Creating a Dictionary
• The syntax for defining a dictionary is:
• dictionary_name = {key_1: value_1, key_2: value2, key_3: value_3}
• Or it can also be written as :
• dictionary_name = { key_1: value_1,
key_2: value_2,
key_3: value_3,
}

4. Points to
remember
The keys in the dictionary must be unique and
of immutable data type i.e. strings, numbers or
tuples.
The value doesn't have any such restrictions.
Dictionary are case-sensitive i.e. two keys with
similar name but different case will be treated
differently.
The elements within the dictionary are
accessed with the help of the keys rather than
its relative position.

5. """Write a program to create a dictionary to convert values from
meters to centimeters
"""
mtocm={m:m*100 for m in range(1,11) }
print("Meters:Centimeters",mtocm)

6. """
Write a program that creates a dictionary of cubes of odd numbers in
the range (1-10)
"""
cubes={c:c**3 for c in range(10) if c%2==1}
print(cubes)

7. """
To count the number of occurrences of each character of a message
entered by the user.
"""
def cnt(msg):
lc={} #empty dictionary
for l in msg:
lc[l]=lc.get(l,0)+1
print(lc)
msg=input("Enter a message ")
cnt(msg)

8. """
Create a dictionary with names of studenst and marks in two papers.Create a dictionaryfinal which has names and total marks and also find the
topper.
"""
result={'Rahul':[78,89],
'Pranamika':[89,87],
'Ashish':[79,88],
'Anshul':[90,67]}
total=0
final=result.copy()
for key,val in result.items():
total=sum(val)
final[key]=total
print(final)
hig=0
Topper=''
for key,val in final.items():
if val>hig:
hig=val
Topper=key
print("Topper is :" , Topper, "securing ", hig, "marks")

9. """
To get the minimum and maximum value from a dictionary
"""
dict = {
'Physics': 90,
'Chemistry':75,
'Maths': 85,
'English':87,
'Computer Sc.':96
}
print('Minimummarks in:', min(dict,key=dict.get))
print('Maximummarks in:', max(dict,key=dict.get))

10. """
Change value of a key in a nested dictionary
"""
dict = {
'emp1': {'name': 'Akash', 'salary': 15500},
'emp2': {'name': 'Ajay', 'salary': 18000},
'emp3': {'name': 'Vijay', 'salary': 16500}
}
dict['emp2']['salary'] = 15500
print(dict)

11. # Program to print sum of key-value # pairs in dictionary
dict = {1: 34, 2: 29, 3: 49}
sumval = []
# Traverse the dictionary
for keys in dict:
sumval.append(keys + dict[keys])
# Print the list
print("Key-value sum =",sumval)

12. # Program for handling missing keys in the dictionary using get() method in Python
# Crating the dictionary
names = {'Sharma' : 'CEO' , 'Saikia' : 'Manager' , 'Ali' : 'Executive'}
# Getting user input for the key
search_key = input("Enter the key to be searched:=> ")
# Logic to handle missing keys in dictionary
print(names.get(search_key, "Search key not present"))

13. # Python program to compare two dictionaries using == operator
emp1 = {'eid': 101, 'ename': 'Rajib', 'eAge': 24}
emp2 = {'eid': 101, 'ename': 'Rajib', 'eAge': 24}
emp3 = {'eid': 102, 'ename': 'Kumar', 'eAge': 25}
if emp1 == emp2:
print("emp1and emp2 are same dictionaries")
else:
print("emp1and emp2 are not same dictionaries")
if emp2 == emp3:
print("emp2and emp3 are same dictionaries")
else:
print("emp2and emp3 are not same dictionaries")

14. # Program to remove a key from dictionary using del in Python
empage = {"Ravi" : 24, "Ashok" : 22, "Vijay" : 25 }
print("The dictionary is :", empage)
del_k = input("Enter the key to be deleted: ")
# Removing the key from dictionary
del empage[del_k]
# Printing the dictionary
print("The dictionary after deletion is : ")
print(empage)

15. # Python program to sort dictionary key and values list
# Creating a list with list as values
result = {'Raju' : [88, 45, 75], 'ram' : [98, 79, 68]}
print("Initially the dictionary is " + str(result))
# Sorting dictionary
sort_res = dict()
for key in sorted(result):
sort_res[key]= sorted(result[key])
# Printing sorted dictionary
print("Dictionary aftersort of key and list value : ")
print(str(sort_res))

16. Thank You