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Python Dictionaries

3 min read ·

A dictionary in Python is a powerful data structure used to store data in key–value pairs. Dictionaries are optimized for fast lookup, making them one of the most important and widely used data types in Python.
This topic covers dictionaries from basics to practical usage.

What Is a Dictionary?

A dictionary:
  • Stores data as key : value pairs
  • Is mutable
  • Does not allow duplicate keys
  • Allows mixed data types
  • Provides fast access using keys

Dictionary vs List vs Tuple vs Set

FeatureListTupleSetDictionary
OrderedYesYesNoYes (Python 3.7+)
MutableYesNoYesYes
DuplicatesYesYesNoKeys: No
AccessIndexIndexNoKey
StructureValuesValuesValuesKey–Value

Creating Dictionaries

Using Curly Braces {}

Using dict() Constructor

Access Dictionary Items

Using Key

Using get() (Safe Access)

Dictionary Keys and Values

Keys Must Be Immutable

Invalid:

Values Can Be Any Data Type

Change Dictionary Items

Add New Items

Remove Dictionary Items

pop()

del

clear()

Loop Through Dictionary

Loop Through Keys

Loop Through Values

Loop Through Key–Value Pairs

Check If Key Exists

Dictionary Length

Nested Dictionaries

Copy a Dictionary

Merge Dictionaries

Dictionary Comprehension

When to Use Dictionaries

Use dictionaries when:
  • Data has a meaningful key
  • Fast lookup is required
  • Data is structured
  • Representing real-world objects

Common Mistakes

Accessing Missing Key Directly

Use get() instead.