KeyError: Missing Dictionary Key

KeyError: 'username'

Quick Answer

You are accessing a dictionary key that does not exist. Use dict.get('key', default) for safe access, or check with 'key' in dict before accessing.

Why This Happens

Accessing a dictionary with dict['key'] raises KeyError if the key is not present. Unlike JavaScript which returns undefined, Python dicts raise an exception.

The Problem

user = {'name': 'Alice', 'email': 'alice@example.com'}
print(user['username'])

The Fix

user = {'name': 'Alice', 'email': 'alice@example.com'}
print(user.get('username', 'N/A'))

Step-by-Step Fix

  1. 1

    Use .get() with a default

    Replace dict['key'] with dict.get('key', default).

  2. 2

    Check key existence

    Use 'key' in dict before accessing.

  3. 3

    Inspect the dictionary

    Print dict.keys() to see available keys.

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