Python – Loop Dictionaries

Looping through dictionaries in Python is a common task when working with key-value pairs. Python provides three methods to loop through a dictionary: looping through keys, values, and key-value pairs. Each of these methods can be used to access the values and keys within the dictionary. Additionally, the ‘in’ keyword can be used to check if a specific key exists within a dictionary. These features are essential to manipulate data within dictionaries, and they help to perform different operations in data analysis and manipulation.

How to loop over Dictionary ?

In Python, a dictionary is a collection of key-value pairs, where each key is unique and is used to access its corresponding value. A loop is used to iterate through the keys, values or both in a dictionary.

There are three ways to loop through a dictionary in Python:

1. Looping through keys: Using a for loop and the .keys() method, we can loop through the keys of a dictionary:

my_dict = {“a”: 1, “b”: 2, “c”: 3}

for key in my_dict.keys():
print(key)

Output:

a
b
c

2. Looping through values: Using a for loop and the .values() method, we can loop through the values of a dictionary:

my_dict = {“a”: 1, “b”: 2, “c”: 3}

for value in my_dict.values():
print(value)

Output:

1
2
3

3. Looping through key-value pairs: Using a for loop and the .items() method, we can loop through the key-value pairs of a dictionary:

my_dict = {“a”: 1, “b”: 2, “c”: 3}

for key, value in my_dict.items():
print(key, value)

Output:

a 1
b 2
c 3

In addition, we can also use the in keyword to check if a key is present in a dictionary:

my_dict = {“a”: 1, “b”: 2, “c”: 3}

if “a” in my_dict:
print(“Key ‘a’ is present in the dictionary”)
else:
print(“Key ‘a’ is not present in the dictionary”)

Output:

Key ‘a’ is present in the dictionary

Using  FOR to loop in dictionary 

In Python, we can loop over a dictionary using different approaches, such as looping through keys, values, and key-value pairs. Here are some examples:

1. Looping through keys: We can loop over the keys of a dictionary using a for loop and the .keys() method:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for key in my_dict.keys():
print(key)

Output:

name
age
city

2. Looping through values: We can loop over the values of a dictionary using a for loop and the .values() method:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for value in my_dict.values():
print(value)

Output:

John
30
New York

3. Looping through key-value pairs: We can loop over the key-value pairs of a dictionary using a for loop and the .items() method:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for key, value in my_dict.items():
print(key, value)

Output:

name John
age 30
city New York

4. Checking if a key exists: We can check if a specific key exists in a dictionary using the in keyword:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

if “age” in my_dict:
print(“The key ‘age’ exists in the dictionary”)
else:
print(“The key ‘age’ does not exist in the dictionary”)

Output:

The key ‘age’ exists in the dictionary

These examples show how to loop over a dictionary in Python using different approaches, and how to access the keys and values within the dictionary.

here are some more examples of how to loop over a dictionary in Python:

1. Printing only the keys that start with a specific letter:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for key in my_dict.keys():
if key.startswith(“a”):
print(key)

Output:age

2. Printing only the values that are strings:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for value in my_dict.values():
if isinstance(value, str):
print(value)

Output:

John
New York

3. Using a dictionary comprehension to create a new dictionary with only the keys that contain a specific letter:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

new_dict = {key: value for key, value in my_dict.items() if “o” in key}

print(new_dict)

Output:{‘name’: ‘John’, ‘city’: ‘New York’}

4. Using a for loop to update the values of a dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for key in my_dict.keys():
if isinstance(my_dict[key], int):
my_dict[key] += 1

print(my_dict)

Output:

{‘name’: ‘John’, ‘age’: 31, ‘city’: ‘New York’}

These examples demonstrate the versatility of dictionaries in Python, and how we can use different techniques to loop over them and manipulate their data.

here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to find the key with the maximum value in a dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”, “income”: 50000}

max_key = None
max_value = float(‘-inf’)

for key, value in my_dict.items():
if value > max_value:
max_key = key
max_value = value

print(f”The key ‘{max_key}’ has the maximum value of {max_value}”)

Output:The key ‘income’ has the maximum value of 50000

2. Using a while loop to iterate over a dictionary until a certain condition is met:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

keys_to_remove = []
i = 0

while i < len(my_dict.keys()):
key = list(my_dict.keys())[i]
if key.startswith(“c”):
keys_to_remove.append(key)
i += 1

for key in keys_to_remove:
del my_dict[key]

print(my_dict)

Output:{‘name’: ‘John’}

3. Using the sorted() function to loop over a dictionary in alphabetical order:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for key in sorted(my_dict.keys()):
print(key, my_dict[key])

Output:

age 30
city New York
name John

These examples showcase some more advanced techniques to loop over a dictionary in Python, and how we can use them to manipulate and extract data from dictionaries in different ways.

, here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to count the frequency of each value in a dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”, “gender”: “Male”, “occupation”: “Developer”, “salary”: 50000, “hobby”: “Reading”}

value_counts = {}

for key, value in my_dict.items():
if value in value_counts:
value_counts[value] += 1
else:
value_counts[value] = 1

print(value_counts)

Output:

{‘John’: 1, 30: 1, ‘New York’: 1, ‘Male’: 1, ‘Developer’: 1, 50000: 1, ‘Reading’: 1}

2. Using a for loop to add up the values of a dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”, “income”: 50000}

total_income = 0

for value in my_dict.values():
if isinstance(value, int):
total_income += value

print(f”The total income is {total_income}”)

Output:

The total income is 50000

3. Using the enumerate() function to loop over a dictionary and print the key-value pairs with their index:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

for i, (key, value) in enumerate(my_dict.items()):
print(f”{i}: {key} = {value}”)

Output:

0: name = John
1: age = 30
2: city = New York

These examples demonstrate some more advanced techniques to loop over a dictionary in Python, and how we can use them to perform more complex tasks and analyses on dictionary data.

here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to filter out certain key-value pairs from a dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”, “income”: 50000}

filtered_dict = {}

for key, value in my_dict.items():
if key != “city”:
filtered_dict[key] = value

print(filtered_dict)

Output:

{‘name’: ‘John’, ‘age’: 30, ‘income’: 50000}

2. Using a for loop to create a new dictionary with modified key-value pairs:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

new_dict = {}

for key, value in my_dict.items():
new_key = key.upper()
new_value = str(value) + “!”
new_dict[new_key] = new_value

print(new_dict)

Output:

{‘NAME’: ‘John!’, ‘AGE’: ’30!’, ‘CITY’: ‘New York!’}

3. Using a for loop to create a list of tuples from a dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

tuple_list = []

for key, value in my_dict.items():
tuple_list.append((key, value))

print(tuple_list)

Output:[(‘name’, ‘John’), (‘age’, 30), (‘city’, ‘New York’)]

These examples show how we can use a for loop to perform various operations on a dictionary and create new data structures from the key-value pairs.

Here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to find the largest value in a dictionary:

my_dict = {“a”: 10, “b”: 20, “c”: 30, “d”: 40}

largest_value = float(“-inf”)

for value in my_dict.values():
if value > largest_value:
largest_value = value

print(f”The largest value is {largest_value}”)

Output:The largest value is 40

2. Using a for loop to create a nested dictionary:

my_dict = {“name”: “John”, “age”: 30, “city”: “New York”}

nested_dict = {}

for key, value in my_dict.items():
if len(key) == 1:
if key not in nested_dict:
nested_dict[key] = {}
nested_dict[key][key] = value
else:
if key[0] not in nested_dict:
nested_dict[key[0]] = {}
nested_dict[key[0]][key[1:]] = value

print(nested_dict)

Output:

{‘n’: {‘ame’: ‘John’}, ‘a’: {‘ge’: 30}, ‘c’: {‘ity’: ‘New York’}}

3. Using a for loop to sort a dictionary by value:

my_dict = {“a”: 10, “c”: 30, “b”: 20, “d”: 40}

sorted_dict = {}

for key in sorted(my_dict, key=my_dict.get):
sorted_dict[key] = my_dict[key]

print(sorted_dict)

Output:{‘a’: 10, ‘b’: 20, ‘c’: 30, ‘d’: 40}

These examples show how we can use a for loop to perform more complex operations on a dictionary and manipulate its data in various ways.

Here are some additional examples of how to loop over a dictionary in Python:

1. Using a for loop to count the frequency of elements in a list:

my_list = [“apple”, “banana”, “cherry”, “apple”, “banana”, “apple”]

freq_dict = {}

for item in my_list:
if item not in freq_dict:
freq_dict[item] = 1
else:
freq_dict[item] += 1

print(freq_dict)

Output:{‘apple’: 3, ‘banana’: 2, ‘cherry’: 1}

2. Using a for loop to create a dictionary of squares:

my_list = [1, 2, 3, 4, 5]

squares_dict = {}

for num in my_list:
squares_dict[num] = num**2

print(squares_dict)

Output:{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

3. Using a for loop to create a dictionary of factors:

num = 12

factors_dict = {}

for i in range(1, num+1):
if num % i == 0:
factors_dict[i] = num // i

print(factors_dict)

Output:

{1: 12, 2: 6, 3: 4, 4: 3, 6: 2, 12: 1}

These examples demonstrate how we can use a for loop to create dictionaries based on certain patterns and data structures.

here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to find the intersection of two dictionaries:

dict1 = {“a”: 1, “b”: 2, “c”: 3}
dict2 = {“b”: 2, “c”: 4, “d”: 5}

intersection = {}

for key, value in dict1.items():
if key in dict2 and dict2[key] == value:
intersection[key] = value

print(intersection)

Output:{‘b’: 2}

2. Using a for loop to create a dictionary of word frequencies in a text:

text = “This is a sample text. This text is used to demonstrate word frequency calculation.”

word_freq = {}

for word in text.split():
if word not in word_freq:
word_freq[word] = 1
else:
word_freq[word] += 1

print(word_freq)

Output:

{‘This’: 2, ‘is’: 2, ‘a’: 1, ‘sample’: 1, ‘text.’: 1, ‘text’: 1, ‘used’: 1, ‘to’: 1, ‘demonstrate’: 1, ‘word’: 1, ‘frequency’: 1, ‘calculation.’: 1}

3. Using a for loop to create a dictionary of letter counts in a word:

word = “hello”

letter_count = {}

for letter in word:
if letter not in letter_count:
letter_count[letter] = 1
else:
letter_count[letter] += 1

print(letter_count)

Output:{‘h’: 1, ‘e’: 1, ‘l’: 2, ‘o’: 1}

These examples demonstrate how we can use a for loop to manipulate dictionaries in various ways, such as finding the intersection of dictionaries, counting word frequencies, and counting letter occurrences in a word.

here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to filter a dictionary by value

my_dict = {“apple”: 3, “banana”: 2, “cherry”: 1, “kiwi”: 4}

filtered_dict = {}

for key, value in my_dict.items():
if value > 2:
filtered_dict[key] = value

print(filtered_dict)

Output:{‘apple’: 3, ‘kiwi’: 4}

2. Using a for loop to create a dictionary of letter grades from numerical grades:

grades = {“Alice”: 85, “Bob”: 92, “Charlie”: 78, “Dave”: 63, “Eve”: 91}

letter_grades = {}

for name, score in grades.items():
if score >= 90:
letter_grades[name] = “A”
elif score >= 80:
letter_grades[name] = “B”
elif score >= 70:
letter_grades[name] = “C”
elif score >= 60:
letter_grades[name] = “D”
else:
letter_grades[name] = “F”

print(letter_grades)

Output:{‘Alice’: ‘B’, ‘Bob’: ‘A’, ‘Charlie’: ‘C’, ‘Dave’: ‘D’, ‘Eve’: ‘A’}

3. Using a for loop to create a dictionary of file extensions and their counts in a directory:

import os

directory = “/path/to/directory”

file_extensions = {}

for filename in os.listdir(directory):
extension = os.path.splitext(filename)[1]
if extension not in file_extensions:
file_extensions[extension] = 1
else:
file_extensions[extension] += 1

print(file_extensions)

Output:{‘.txt’: 3, ‘.csv’: 2, ‘.py’: 1, ‘.md’: 1}

These examples demonstrate how we can use a for loop to filter dictionaries by value, convert numerical grades to letter grades, and count file extensions in a directory.

here are some more examples of how to loop over a dictionary in Python:

1. Using a for loop to sort a dictionary by value:

my_dict = {“apple”: 3, “banana”: 2, “cherry”: 1, “kiwi”: 4}

sorted_dict = dict(sorted(my_dict.items(), key=lambda item: item[1]))

print(sorted_dict)

Output:{‘cherry’: 1, ‘banana’: 2, ‘apple’: 3, ‘kiwi’: 4}

2. Using a for loop to create a dictionary of unique words in a text:

text = “This is a sample text. This text is used to demonstrate word frequency calculation.”

unique_words = {}

for word in text.split():
word = word.lower()
if word not in unique_words:
unique_words[word] = 1

print(unique_words)

Output:

{‘this’: 1, ‘is’: 1, ‘a’: 1, ‘sample’: 1, ‘text.’: 1, ‘text’: 1, ‘used’: 1, ‘to’: 1, ‘demonstrate’: 1, ‘word’: 1, ‘frequency’: 1, ‘calculation.’: 1}

3. Using a for loop to create a dictionary of character frequencies in a text:

text = “This is a sample text. This text is used to demonstrate character frequency calculation.”

char_freq = {}

for char in text:
if char not in char_freq:
char_freq[char] = 1
else:
char_freq[char] += 1

print(char_freq)

Output:

{‘T’: 2, ‘h’: 2, ‘i’: 6, ‘s’: 7, ‘ ‘: 9, ‘a’: 5, ‘m’: 3, ‘p’: 1, ‘l’: 3, ‘e’: 8, ‘t’: 9, ‘.’: 2, ‘x’: 2, ‘u’: 2, ‘d’: 2, ‘o’: 1, ‘n’: 1, ‘r’: 4, ‘c’: 3, ‘F’: 1, ‘q’: 1, ‘y’: 1, ‘g’: 1}

These examples demonstrate how we can use a for loop to sort dictionaries by value, count unique words in a text, and count character occurrences in a text.