Dictionary Python – Great Learning


Dictionaries in Python come tremendous useful as they allow you to retailer and set up knowledge in a versatile approach. Think of it as a real-life dictionary the place you may seek for phrases and discover their meanings. With dictionaries, you may affiliate “keys” with “values.”  The keys are just like the phrases you’re trying up, and the values are the meanings that associate with these phrases. 

Dictionaries present quick and environment friendly knowledge retrieval based mostly on keys. Python makes use of hashing to shortly find the worth related to a given key, making dictionaries ideally suited for accessing particular knowledge shortly. Secondly, dictionaries help you set up and construction your knowledge logically. Additionally, you get a concise and readable strategy to signify advanced relationships and mappings between completely different entities. 

Let’s study extra about creating, accessing, modifying, and updating dictionaries together with their operations and comprehensions. We’ll additionally find out about nested dictionaries, dictionary manipulation strategies, built-in capabilities and a lot extra.

Creating and Accessing Dictionaries

Let’s dive into creating and accessing dictionaries in Python. 

Dictionary Syntax and Structure

Dictionaries are outlined utilizing curly braces ({}) and include key-value pairs. The key-value pairs are separated by colons (:) and particular person pairs are separated by commas. The keys could be any immutable knowledge sort, akin to strings, numbers, or tuples, whereas the values could be any knowledge sort, together with lists, strings, numbers, and even different dictionaries.

Dictionary Creation and Initialization

Let’s say we wish to create a dictionary to retailer the ages of various individuals. Here’s tips on how to do it:

ages = {"Alice": 25, "Bob": 30, "Charlie": 35}

Here, we now have a dictionary known as ages with three key-value pairs. The keys are the names of individuals, and the corresponding values are their ages.

Accessing Values Using Keys

To entry the values in a dictionary, you need to use the keys because the “index” to retrieve the related values. Let’s proceed with our ages dictionary instance:

print(ages["Alice"])  # Output: 25

print(ages["Bob"])    # Output: 30

print(ages["Charlie"])# Output: 35

By utilizing the respective keys in sq. brackets, we will entry the values related to these keys. In this case, we retrieve the ages of Alice, Bob, and Charlie.

Handling Missing Keys and Default Values

Sometimes, you might have to deal with conditions the place a key doesn’t exist in a dictionary. To keep away from errors, you need to use the get() technique or conditional statements. The get() technique permits you to specify a default worth to return if the secret’s not discovered:

print(ages.get(“Dave”, “Unknown”))  # Output: Unknown

Here, the important thing “Dave” doesn’t exist within the age dictionary. By utilizing get(), we offer a default worth of “Unknown” to be returned as a substitute.

Alternatively, you need to use conditional statements to examine if a key exists in a dictionary earlier than accessing its worth:

if “Alice” in ages:

    print(ages["Alice"])  # Output: 25


    print("Alice's age just isn't out there.")

Here, we examine if the important thing “Alice” is current within the ages dictionary earlier than accessing its worth. If the important thing exists, we print the related age; in any other case, we show a message indicating that the age just isn’t out there.

Modifying and Updating Dictionaries

Let’s learn to modify and replace dictionaries.

Adding and Removing Key-Value Pairs

Dictionaries are mutable, that means you may modify them by including or eradicating key-value pairs. To add a brand new key-value pair, you may merely assign a worth to a brand new or current key:

pupil = {"title": "Alice", "age": 25}

pupil["grade"] = "A"

Here, we now have a dictionary known as pupil with two key-value pairs. We then add a brand new key known as “grade” and assign the worth “A” to it. The dictionary now has three key-value pairs.

To take away a key-value pair, you need to use the del key phrase adopted by the dictionary title and the important thing you wish to take away:

del pupil["age"]

Here, we take away the important thing “age” and its related worth from the coed dictionary. After this, the dictionary solely accommodates the “name” and “grade” key-value pairs.

Updating Values for Existing Keys

If you wish to replace the worth of an current key in a dictionary, you may merely reassign a brand new worth to that key:

pupil["grade"] = "A+"

Here, we replace the worth of the “grade” key to “A+”. The dictionary is modified to mirror the up to date worth for the important thing.

Merging Dictionaries utilizing the replace() Method

You can merge the contents of two dictionaries into one through the use of the replace() technique. Let’s say we now have two dictionaries, dict1 and dict2, and we wish to merge them into a brand new dictionary known as merged_dict:

dict1 = {"a": 1, "b": 2}

dict2 = {"c": 3, "d": 4}

merged_dict = {}



Here, we create an empty dictionary known as merged_dict after which use the replace() technique so as to add the key-value pairs from dict1 and dict2. After executing this code, merged_dict will include all of the key-value pairs from each dict1 and dict2.

Common Dictionary Operations and Methods

By mastering these widespread operations and strategies, you’ll be outfitted to work effectively with dictionaries in Python. Whether it’s good to iterate over gadgets, examine for key existence, extract keys or values, or discover the size of a dictionary, these strategies will show helpful in numerous programming eventualities.

Iterating over Dictionary Items

It permits you to entry each the keys and their corresponding values. You can use a loop, akin to a for loop, to iterate over the gadgets. Here’s an instance:

pupil = {"title": "Alice", "age": 25, "grade": "A"}

for key, worth in pupil.gadgets():

    print(key, worth)

Here, we iterate over the gadgets of the coed dictionary utilizing the gadgets() technique. Within the loop, we entry every key-value pair and print them. This permits you to carry out operations on every merchandise or extract particular info from the dictionary.

Checking for the Existence of Keys

Sometimes, you might have to examine if a particular key exists in a dictionary. You can use the in key phrase to carry out this examine. Let’s see an instance:

pupil = {"title": "Alice", "age": 25, "grade": "A"}

if "age" in pupil:

    print("Age exists within the dictionary.")


    print("Age doesn't exist within the dictionary.")

Here, we examine if the important thing “age” exists within the pupil dictionary utilizing the in key phrase. If the secret’s current, we print a message indicating its existence; in any other case, we print a message indicating its absence.

Getting Keys, Values, or Both from a Dictionary

There are helpful strategies out there to extract keys, values, or each from a dictionary. Here are some examples:

pupil = {"title": "Alice", "age": 25, "grade": "A"}

keys = pupil.keys()

values = pupil.values()

gadgets = pupil.gadgets()

print(keys)   # Output: dict_keys(['name', 'age', 'grade'])

print(values) # Output: dict_values(['Alice', 25, 'A'])

print(gadgets)  # Output: dict_items([('name', 'Alice'), ('age', 25), ('grade', 'A')])

Here, we use the keys(), values(), and gadgets() strategies to acquire the keys, values, and key-value pairs as separate objects. These strategies return particular views that help you entry the dictionary’s keys, values, or gadgets in a handy approach.

Finding the Length of a Dictionary

To decide the variety of key-value pairs in a dictionary, you need to use the len() perform. Here’s an instance:

pupil = {"title": "Alice", "age": 25, "grade": "A"}

size = len(pupil)

print(size)  # Output: 3

Here, we calculate the size of the coed dictionary utilizing the len() perform. The perform returns the variety of key-value pairs within the dictionary.

Dictionary Comprehensions

Dictionary comprehensions are a concise and environment friendly strategy to create dictionaries in Python. They comply with the same idea to checklist comprehensions however help you create dictionaries with key-value pairs in a single line of code. Dictionary comprehensions present a clear and readable syntax for producing dictionaries based mostly on particular situations or transformations.

Creating Dictionaries Using Comprehensions

To create a dictionary utilizing a comprehension, it’s good to outline the key-value pairs inside curly braces ({}) and specify the key-value expression. 

squares = {x: x**2 for x in vary(1, 6)}

Here, we create a dictionary known as squares utilizing a comprehension. The expression x: x**2 represents the key-value pairs, the place the secret’s x and the worth is x**2. We iterate over a spread from 1 to six and generate key-value pairs the place the keys are the numbers and the values are their squares. The ensuing dictionary will appear to be this: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}.

Advantages and Use Cases of Dictionary Comprehensions:

Dictionary comprehensions provide a number of benefits and can be utilized in numerous eventualities, akin to:

  • Concise and Readable Code: Dictionary comprehensions allow you to specific advanced logic or transformations in a single line of code, enhancing code readability and making your intentions clear.
  • Filtering and Transformation: It can be utilized to filter or modify knowledge. This lets you create dictionaries based mostly on particular necessities.
  • Efficient Data Generation: You can generate dictionaries effectively, lowering the quantity of code and enhancing efficiency.
  • Data Restructuring: Dictionary comprehensions are useful when it’s good to restructure knowledge from one format to a different. You can map current keys to new values and even swap keys and values throughout the comprehension.

Nested Dictionaries

A nested dictionary is a dictionary that accommodates one other dictionary (or dictionaries) as its values. This permits for a hierarchical construction, the place you may set up and retailer associated knowledge throughout the nested ranges. In different phrases, the values of a dictionary could be dictionaries themselves.

Accessing and Modifying Values in Nested Dictionaries

To entry values in a nested dictionary, you need to use a number of sq. brackets to specify the keys at every degree. Here’s an instance:

college students = {

    "Alice": {

        "age": 25,

        "grade": "A"


    "Bob": {

        "age": 30,

        "grade": "B"



print(college students["Alice"]["age"])  # Output: 25

Here, we now have a dictionary known as college students, the place every key represents a pupil’s title, and the corresponding worth is a nested dictionary containing the coed’s age and grade. By utilizing a number of sq. brackets, we will entry particular values throughout the nested ranges.

To modify values in a nested dictionary, you may comply with the same strategy. For instance:

college students["Alice"]["grade"] = "A+"

Here, we replace the worth of the “grade” key for the coed named “Alice” to “A+”. This modification applies on to the nested dictionary inside the principle dictionary.

Examples of Nested Dictionary

Nested dictionaries could be helpful in numerous eventualities. Here are just a few examples:

  • Managing Student Records: You can use a nested dictionary construction to retailer pupil info, akin to names, ages, and grades. Each pupil’s particulars could be represented by a nested dictionary inside the principle dictionary.
  • Organizing Inventory Data: If you’re engaged on a listing administration system, nested dictionaries could be useful for organizing product particulars. Each product can have its personal dictionary containing attributes like title, value, amount, and so forth.
  • Storing Multi-Level Configuration Settings: When coping with configuration settings, you might have a number of ranges of settings, akin to sections and subsections. A nested dictionary can signify this hierarchical construction, permitting you to entry and modify settings at completely different ranges simply.

Dictionary Manipulation Techniques

Let’s discover some useful strategies for manipulating dictionaries in Python.

Sorting Dictionaries by Keys or Values

Python offers handy strategies to type dictionaries based mostly on both their keys or values. Here are a few examples:

To type a dictionary by its keys, you need to use the sorted() perform together with the keys() technique. Here’s an instance:

student_grades = {"Alice": 85, "Bob": 92, "Charlie": 78}

sorted_by_keys = {key: student_grades[key] for key in sorted(student_grades.keys())}

Here, we create a brand new dictionary known as sorted_by_keys by iterating over the keys of the student_grades dictionary in sorted order. This will lead to a dictionary with the keys sorted alphabetically: {“Alice”: 85, “Bob”: 92, “Charlie”: 78}.

To type a dictionary by its values, you need to use the sorted() perform with a lambda perform as the important thing parameter. Here’s an instance:

student_grades = {"Alice": 85, "Bob": 92, "Charlie": 78}

sorted_by_values = {key: worth for key, worth in sorted(student_grades.gadgets(), key=lambda merchandise: merchandise[1])}

Here, we create a brand new dictionary known as sorted_by_values by sorting the gadgets of the student_grades dictionary based mostly on their values utilizing a lambda perform. The ensuing dictionary will likely be sorted in ascending order by values: {“Charlie”: 78, “Alice”: 85, “Bob”: 92}.

Filtering Dictionaries Based on Certain Criteria

You can filter dictionaries based mostly on particular standards utilizing conditional statements and dictionary comprehensions. Here’s an instance:

student_grades = {"Alice": 85, "Bob": 92, "Charlie": 78}

filtered_grades = {key: worth for key, worth in student_grades.gadgets() if worth >= 80}

Here, we create a brand new dictionary known as filtered_grades by iterating over the gadgets of the student_grades dictionary and together with solely these with values better than or equal to 80. The ensuing dictionary will include solely the key-value pairs that fulfill the given situation: {“Alice”: 85, “Bob”: 92}.

Creating a Dictionary from Two Lists utilizing zip()

You can create a dictionary by combining two lists utilizing the zip() perform. Here’s an instance:

names = ["Alice", "Bob", "Charlie"]

ages = [25, 30, 28]

combined_dict = {title: age for title, age in zip(names, ages)}

Here, we use zip() to mix the names and ages lists, after which create a brand new dictionary known as combined_dict. Each title from the names checklist turns into key, and every corresponding age from the ages checklist turns into the respective worth within the dictionary: {“Alice”: 25, “Bob”: 30, “Charlie”: 28}.

Dictionary Methods and Built-in Functions

Whether it’s good to entry keys, values, or gadgets, retrieve particular values, take away entries, or carry out normal operations like discovering the size or most/minimal values, these strategies and capabilities have gotten you coated.

Commonly Used Dictionary Methods

  • keys(): It returns a view object that accommodates all of the keys of a dictionary. This permits you to entry and iterate over the keys conveniently.
  • values(): It returns a view object that accommodates all of the values of a dictionary. It offers a strategy to entry and iterate over the values saved within the dictionary.
  • gadgets(): It returns a view object that accommodates all of the key-value pairs of a dictionary as tuples. It permits you to entry and iterate over the key-value pairs collectively.
  • get(key, default): It retrieves the worth related to a particular key within the dictionary. If the secret’s not discovered, it returns a default worth as a substitute of elevating an error.
  • pop(key, default): It removes and returns the worth related to a particular key from the dictionary. If the secret’s not discovered, it returns a default worth or raises a KeyError if no default worth is supplied.

Built-in Functions for Dictionaries

  • len(): It returns the variety of key-value pairs in a dictionary. It’s a handy strategy to decide the dimensions or size of a dictionary.
  • max(): It can be utilized to search out the utmost key or worth in a dictionary, based mostly on their pure ordering. It’s helpful when it’s good to discover the most important key or worth in a dictionary.
  • min(): It works equally to max(), however it finds the minimal key or worth in a dictionary based mostly on their pure ordering.

Advanced Dictionary Techniques

By understanding these superior strategies, you may broaden your dictionary expertise and use dictionaries extra successfully in Python. 

Handling Dictionary Collisions and Hash Functions

In Python, dictionaries use hash capabilities to map keys to particular places throughout the underlying knowledge construction. Occasionally, two keys might produce the identical hash worth, leading to a collision. Python handles these collisions routinely, however it’s useful to know the ideas.

Hash capabilities are answerable for producing hash codes, distinctive identifiers related to every key. Python’s built-in hash perform produces these hash codes. When a collision happens, Python makes use of a method known as open addressing or chaining to resolve it.

As a person, you don’t want to fret an excessive amount of about dealing with collisions or hash capabilities straight. Python’s dictionary implementation takes care of this complexity behind the scenes, making certain environment friendly key-value lookups and updates.

Working with Dictionaries as Function Arguments and Return Values

Dictionaries are versatile knowledge buildings that may be handed as arguments to capabilities and returned as perform outcomes. This permits for versatile and dynamic interactions. 

  • Passing Dictionaries as Function Arguments:

It lets you present key-value pairs as inputs. This is especially helpful when you could have a various variety of arguments or wish to bundle associated knowledge collectively. Functions can then entry and make the most of the dictionary’s contents as wanted.

  • Returning Dictionaries from Functions:

Functions can even return dictionaries as their outcomes. This permits you to encapsulate and supply computed or processed knowledge in a structured method. The calling code can then entry and make the most of the returned dictionary to retrieve the specified info.

Working with dictionaries in perform arguments and return values promotes flexibility and modularity in your code. It permits for straightforward communication of knowledge between completely different components of your program.

Customizing Dictionaries utilizing OrderedDict and defaultdict

Python offers further dictionary variants that provide customization past the usual dictionary implementation. Let’s discover two such variants:

The OrderedDict class maintains the order during which key-value pairs are inserted. Standard dictionaries don’t assure any particular order. By utilizing OrderedDict, you may iterate over the key-value pairs within the order they have been added. This could be useful when order issues, akin to preserving the order of parts in a configuration or processing steps.

The defaultdict class, out there within the collections module, offers a default worth for keys that don’t exist within the dictionary. This eliminates the necessity for guide checks to deal with lacking keys. You can specify the default worth when making a defaultdict. This is especially helpful when working with counters, frequency distributions, or grouping knowledge.

Real-world Examples and Applications

Let’s discover some real-world examples and functions of dictionaries in Python. 

Data Manipulation

Dictionaries are glorious for organizing and manipulating knowledge. For occasion, think about you could have a dataset of scholars with their names, grades, and topics. You can use dictionaries to signify every pupil, the place the title is the important thing and the related values include their grade and topics. This permits you to simply entry and replace particular person pupil information.

Configuration Settings

Dictionaries are generally used to retailer and handle configuration settings in functions. For occasion, you may create a dictionary to carry numerous settings, such because the database connection particulars, file paths, and person preferences. By utilizing key-value pairs, you may simply entry and modify these settings all through your program.

Dictionaries can be highly effective instruments for fixing programming issues. Here are just a few examples:

Counting and Frequency Analysis

Dictionaries are sometimes employed for counting occurrences and performing frequency evaluation. For occasion, you need to use a dictionary to depend the frequency of phrases in a textual content doc or monitor the prevalence of characters in a string, which could be useful for numerous textual content processing duties.

Grouping and Categorization

Dictionaries are helpful for grouping and categorizing knowledge based mostly on particular standards. For occasion, you need to use dictionaries to group college students by their grades, staff by departments, or merchandise by classes. This permits for environment friendly knowledge group and retrieval.


Memoization is a method used to optimize perform calls by storing the outcomes of high-priced computations. Dictionaries are sometimes employed as a cache to retailer beforehand computed values. By utilizing the enter arguments as keys and the computed outcomes as values, you may keep away from redundant computations and enhance the efficiency of your code.

Concluding Thoughts

We’ve coated numerous elements of dictionaries in Python, exploring key ideas and demonstrating their sensible functions. We’ve seen tips on how to create and entry dictionaries, modify and replace their contents, carry out widespread operations and strategies, make the most of superior strategies, and apply dictionaries to real-world eventualities and programming issues.

By now, it is best to have a stable understanding of how dictionaries work and their advantages. However, there’s all the time extra to study and uncover! Dictionaries provide an enormous array of potentialities, and we encourage you to proceed exploring and experimenting with them. Try completely different strategies, mix dictionaries with different knowledge buildings, and apply them to unravel various challenges.


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