Dictionaries

Dictionaries store key-value pairs with {}. Keys must be immutable and unique.

Access

dict[key] or dict.get(key, default)

Methods

• keys(), values(), items()
• update(), pop(), setdefault()

Syntax

PYTHON

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person = {"name": "Alice", "age": 25}
print(person["name"])
print(person.get("phone", "N/A"))
person["email"] = "alice@mail.com"
for k, v in person.items():
    print(f"{k}: {v}")

Python Dictionaries

PYTHON

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person = {
    "name": "Alice",
    "age": 25,
    "city": "New York"
}

print("Name:", person["name"])
print("Get:", person.get("email", "not found"))

# Add / update
person["email"] = "alice@example.com"
print("Updated keys:", list(person.keys()))

# Iterate
for key, value in person.items():
    print(f"{key}: {value}")

# Nested
company = {
    "name": "SukhNexus",
    "employees": [
        {"name": "Bob", "role": "Developer"},
        {"name": "Eve", "role": "Designer"}
    ]
}
print("Role:", company["employees"][0]["role"])

Try It Yourself

Practice

1

Exercise

Count character frequencies in a string.

Answer

text = "hello"
for c in set(text):
    print(f"{c}: {text.count(c)}")

Quick Quiz

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What does dict[key] do for missing keys?

Returns None

Raises KeyError

Returns ""

Raises KeyError. Use .get() for safe access.

Retry Quiz

Interview Questions

How does dict lookup achieve O(1)?

Hash tables map keys to storage locations via hash functions.

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