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Wrong syntax for adding a new key

🐛 Fix the bug Topic: dictionaries Difficulty: easy Free

What this problem practises

Dictionaries fail loudly on a missing key with KeyError, quietly through get(), and in genuinely surprising ways when you modify a dict while iterating it or rely on a duplicate key silently replacing the earlier entry.

This is a fix-the-bug problem: a short program is given in its broken state, and the task is to repair the code so it produces the required output. The interactive editor runs your fixed version in the browser and checks it for you — no setup, no local interpreter.

Difficulty: easy — the fix or the trick is normally a single line, and a careful read should be enough.

The challenge

This should add a new key-value pair, but crashes. Fix it.

The code runs in PyDebug’s in-browser compiler. Open the problem, run the snippet, watch the exact error or output, and keep iterating until it is right. Signed-in solves count toward XP and your daily streak.

The error it raises

Run the broken snippet and Python stops with this exact error: SyntaxError: cannot assign to function call here. Match it to the Python errors guide, then repair the line that produced it — knowing the message is half the fix.

The snippet

The interactive editor pre-fills exactly this code, broken and ready to repair:

person = {"name": "Aditi"}
person("age") = 24
print(person)

Understand the rule

Adding a key to a dictionary is plain assignment: data['city'] = 'Pune'. The broken version calls methods that do not exist (data.add(...), data.append(...) — AttributeError) or uses add-syntax borrowed from sets and lists. There is no 'insert' method for a single key on purpose: assignment already creates the key if absent and updates it if present.

How to trace it

Read which method the AttributeError names; add() belongs to sets, append() to lists — the object here is a dict.
Use subscript assignment: data[key] = value creates or overwrites in one step.
For many pairs at once, data.update({...}) or dict unpacking {**a, **b} merges them.
If 'only add when missing' is the intent, data.setdefault(key, value) expresses exactly that.

Common wrong fixes

Expecting data[key] = value to fail when the key exists; it silently overwrites, which may or may not be wanted.
Building a one-pair dict and forgetting to merge it: {key: value} alone does not touch data.
Using update() with keyword syntax for non-string keys, which only works for identifier-like string keys.

Rule to remember

dict[key] = value is the canonical way to add or replace one entry; update() merges many. add() and append() are set and list vocabulary — the AttributeError is telling you which type you are really holding.

Solve it in the interactive editor →

📦 Learning path: Lists and Dictionaries

Problem 18 of 20 in this path. Work them in order — each one builds on the rule before it.

← Deleting a key that doesn't exist Next in path: Dictionary keys must be unique →

Keep going

Python debugging guide — a systematic method for finding bugs like this one fast.
Browse every dictionaries problem in this topic.
Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.