Python TypedDict Required, NotRequired, and ReadOnly Keys

Required and NotRequired express whether individual TypedDict keys must be present, while ReadOnly marks an item as non-writable for static checkers.

What It Does and Why It Matters

Required and NotRequired express whether individual TypedDict keys must be present, while ReadOnly marks an item as non-writable for static checkers. These annotations do not freeze a dict during execution.

Step-by-Step Example

Start with the complete example below. Read the inputs and predict what the final print statement will show before you run it.

from typing import NotRequired, ReadOnly, TypedDict
class JobRecord(TypedDict):
    identifier: ReadOnly[int]
    note: NotRequired[str]
job_record: JobRecord = {'identifier': 17}
print(job_record.get('note', 'no note'))

How the Code Works

The imports make these standard-library tools available: typing.
The definition of JobRecord creates reusable behavior; its body runs only when called or instantiated as appropriate.
The name job_record receives the value of {'identifier': 17}. Changing this input lets you explore a different case.
The print calls display the results. Compare these results with the method’s documented return type and the input used.
The annotations describe intended types for editors and checkers. They are not a replacement for validating input values when the function runs.

Expected output:

no note

For the demonstrated inputs, Python displays 'no note'. This result follows from the operation described above; change one input at a time to understand which rule matters.

What to Notice

Pay attention to the accepted input types, the returned value and the boundary behavior. Predict what changes if you replace the example input with an empty, zero, negative or missing value, where that value is meaningful for this operation.

If the task uses a library function, inspect its documented exceptions and return type before reusing it inside a larger function.

Where You Would Use This

This helps maintain larger projects where functions and data shapes cross module boundaries. Check the code with a static analyzer, and still validate data received from files, users or remote APIs. Annotation constructs do not normally enforce types automatically at runtime.

Practice Exercise

Create a record with one required field and an optional note.

Before running your edited example, write down the result you expect. Then test at least one valid boundary or deliberately invalid value, using appropriate exception handling where necessary.

Reference: official Python documentation for the complete API contract and version notes.

Common Beginner Mistakes

Treating optional-key access as guaranteed safe or expecting ReadOnly to be enforced at runtime.
Overlooking the documented condition: required and NotRequired express whether individual TypedDict keys must be present, while ReadOnly marks an item as non-writable for static checkers.

Key Takeaways

Required and NotRequired express whether individual TypedDict keys must be present, while ReadOnly marks an item as non-writable for static checkers.
Create a record with one required field and an optional note.