Loop Dictionaries
Looping Through Dictionaries
A dictionary can be looped through in different ways. By default, iterating over a dictionary loops through its keys. You can also explicitly loop over keys, values, or key-value pairs.
Example
# Looping through a dictionary
person = {"name": "John", "age": 30, "city": "New York"}
# Loop through keys (default)
print("Keys:")
for key in person:
print(f"- {key}")
# Loop through keys explicitly
print("\nKeys (explicit):")
for key in person.keys():
print(f"- {key}: {person[key]}")
# Loop through values
print("\nValues:")
for value in person.values():
print(f"- {value}")
# Loop through key-value pairs
print("\nItems:")
for key, value in person.items():
print(f"- {key}: {value}")Output
Keys: - name - age - city Keys (explicit): - name: John - age: 30 - city: New York Values: - John - 30 - New York Items: - name: John - age: 30 - city: New York
Dictionary Comprehensions
Dictionary comprehensions provide a concise way to build or transform dictionaries. They follow the pattern `{key: value for ...}` and can include conditions for filtering.
Example
# Dictionary comprehensions
numbers = [1, 2, 3, 4, 5]
# Create dictionary with squares
squares = {x: x**2 for x in numbers}
print("Squares:", squares)
# Filter dictionary by key length
person = {"name": "John", "age": 30, "city": "New York", "country": "USA"}
filtered = {k: v for k, v in person.items() if len(k) > 3}
print("Filtered:", filtered)
# Transform string values to uppercase
transformed = {k: v.upper() if isinstance(v, str) else v for k, v in person.items()}
print("Transformed:", transformed)Output
Squares: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
Filtered: {'name': 'John', 'city': 'New York', 'country': 'USA'}
Transformed: {'name': 'JOHN', 'age': 30, 'city': 'NEW YORK', 'country': 'USA'}Nested Loops with Dictionaries
Dictionaries can hold nested structures such as other dictionaries or lists. You can use nested loops to access and process these values.
Example
# Nested loops with dictionaries
students = {
"John": {"age": 20, "grades": [85, 90, 78]},
"Jane": {"age": 21, "grades": [92, 88, 95]},
"Bob": {"age": 19, "grades": [76, 82, 80]}
}
# Calculate average grade for each student
for name, info in students.items():
avg_grade = sum(info["grades"]) / len(info["grades"])
print(f"{name}: Age {info['age']}, Average Grade: {avg_grade:.1f}")Output
John: Age 20, Average Grade: 84.3 Jane: Age 21, Average Grade: 91.7 Bob: Age 19, Average Grade: 79.3