Introduction to Dictionaries

Creating Dictionaries

d = {"name": "Ana", "age": 20}
d = dict(name="Ana", age=20)
d = {}  # Empty dict

Accessing Values

d["name"]           # "Ana" (KeyError if missing)
d.get("name")       # "Ana"
d.get("grade", 0)   # 0 (default if missing)

Modification

d["age"] = 21       # Modify
d["grade"] = 9      # Add new
del d["grade"]      # Delete

Key Membership

"name" in d         # True (checks KEYS)
"Ana" in d          # False (Ana is value, not key)

Iteration

for key in d:            # Keys
for key in d.keys():     # Keys (explicit)
for val in d.values():   # Values
for k, v in d.items():   # Key-value pairs

Key Points

• Keys must be hashable (immutable)
• [] raises KeyError, .get() returns None
• in checks keys, not values