Python dir() Function: Usage and Examples

Inspect available attribute names with the built-in dir() function.

What You Will Learn

dir(value) returns a sorted list of names supplied by the object’s introspection machinery, often including inherited and special attributes. It is useful for exploration but is not a complete contract for dynamic attributes.

Use help() and official docs for supported method behavior, not dir() alone.

Step-by-Step Example

The example below makes the behavior visible with small input values that you can change safely.

class Monitor:
    def check(self):
        return True

monitor = Monitor()
print("check" in dir(monitor))
print("__class__" in dir(monitor))

How the Example Works

The class Monitor groups data and behavior; its methods run when called on an instance.
The variable monitor holds the result of Monitor(). Later lines use that value or inspect how it changes.
The print() calls make the return values or state visible so you can compare them with the explanation and check your prediction.

Expected output from the example:

True
True

Another Example: Compare the Results

Try a second input and compare it with the first. Notice whether the result changes in type, value, order, or number of items.

print("upper" in dir("sample"))
print("missing" in dir("sample"))

Expected output:

True
False

When You Would Use This

These tools are useful when composing small reusable functions, adapting callbacks, or eliminating repeated work. Pay attention to whether the operation returns a new object, updates state, or produces lazy results. Test a small success case and a boundary case before integrating it into an application.

Practice: Modify the Code

Find the names of public methods on a toy class.

Verify the changed output against the behavior described above, including the relevant invalid or boundary case.

For complete parameters and version details, consult the official Python documentation.

Common Beginner Mistakes

Assuming every name from dir() is public, stable, and safe to call.
Treating absence from dir() as proof that dynamic lookup cannot succeed.

Key Takeaways

Inspect available attribute names with the built-in dir() function.
dir(value) returns a sorted list of names supplied by the object’s introspection machinery, often including inherited and special attributes.
Use help() and official docs for supported method behavior, not dir() alone.