Python Basics — Dictionary Methods

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Dictionary Methods

Python dictionaries come with powerful built-in methods for accessing, iterating, and transforming data.

View Methods

.keys() — All Keys

user = {"name": "Alice", "age": 30, "city": "New York"}

print(user.keys())
# dict_keys(['name', 'age', 'city'])

# Convert to list
print(list(user.keys()))  # ['name', 'age', 'city']

.values() — All Values

print(user.values())
# dict_values(['Alice', 30, 'New York'])

.items() — All Key-Value Pairs

print(user.items())
# dict_items([('name', 'Alice'), ('age', 30), ('city', 'New York')])

These return view objects that reflect changes to the dictionary in real time.

.update() — Merge Dictionaries

user = {"name": "Alice", "age": 30}

# Update with another dict
user.update({"age": 31, "email": "alice@example.com"})
print(user)
# {'name': 'Alice', 'age': 31, 'email': 'alice@example.com'}

# Update with keyword arguments
user.update(city="New York")
print(user)
# {'name': 'Alice', 'age': 31, 'email': 'alice@example.com', 'city': 'New York'}

.clear() — Remove All Items

d = {"a": 1, "b": 2, "c": 3}
d.clear()
print(d)  # {}

.copy() — Shallow Copy

original = {"a": 1, "b": [2, 3]}
copy = original.copy()

copy["a"] = 99
print(original["a"])  # 1 (unchanged)

# But nested objects are shared!
copy["b"].append(4)
print(original["b"])  # [2, 3, 4] (changed!)

Iterating Over Dictionaries

Keys (default)

user = {"name": "Alice", "age": 30, "city": "New York"}

for key in user:
    print(key)
# name
# age
# city

Values

for value in user.values():
    print(value)
# Alice
# 30
# New York

Key-Value Pairs

for key, value in user.items():
    print(f"{key}: {value}")
# name: Alice
# age: 30
# city: New York

Merging Dictionaries

Using | Operator (Python 3.9+)

defaults = {"theme": "light", "font_size": 14}
custom = {"font_size": 16, "language": "en"}

merged = defaults | custom
print(merged)
# {'theme': 'light', 'font_size': 16, 'language': 'en'}

The right side wins for duplicate keys.

Using |= (In-place Merge)

defaults = {"theme": "light", "font_size": 14}
defaults |= {"font_size": 16, "language": "en"}
print(defaults)
# {'theme': 'light', 'font_size': 16, 'language': 'en'}

Using ** Unpacking

defaults = {"theme": "light", "font_size": 14}
custom = {"font_size": 16, "language": "en"}

merged = {**defaults, **custom}
print(merged)
# {'theme': 'light', 'font_size': 16, 'language': 'en'}

Using .update()

merged = defaults.copy()
merged.update(custom)

Complete Methods Reference

Method Description Returns
d.keys() All keys dict_keys view
d.values() All values dict_values view
d.items() Key-value pairs dict_items view
d.get(k, default) Value for key Value or default
d.setdefault(k, v) Get or set Value
d.update(other) Merge in-place None
d.pop(k, default) Remove and return Value
d.popitem() Remove last pair (key, value) tuple
d.clear() Remove all None
d.copy() Shallow copy New dict
d.fromkeys(keys, v) New dict from keys New dict

Summary

  • .keys(), .values(), .items() return live view objects
  • .update() merges another dict (or kwargs) in-place
  • | operator merges dicts (Python 3.9+), right side wins
  • .copy() creates a shallow copy (nested objects shared)
  • Iterate with for key, value in d.items():

Next up: Dictionary Comprehensions →

Updated:

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