Readable diagnostics
Investigating values during debugging
Python · Function
repr
repr(object) returns a printable string representation of an object. For many types it aims to produce text that can recreate an equal-valued object with eval(), while other objects use a descriptive fallback.
How it works
repr(object) produces a string intended to be a printable representation of the supplied object. For many built-in types, that string is designed so evaluating it recreates an object with the same value; other objects may use an angle-bracket description instead.
Syntax
repr(object, /)Parameters
| Name | Type | Description |
|---|---|---|
object | object | The object whose printable representation is requested. |
Returns
A string containing a printable representation of the object.
Key points
- The result is always a string intended to show the object in a printable form.
- For many types, Python aims for a representation that can recreate an equal-valued object.
- The documented reconstruction convention uses
eval()applied to the representation string. - Custom classes can define the representation behavior used by
repr().
Common mistakes
- Do not assume every result is executable Python: objects without a suitable value-oriented representation can produce an angle-bracket diagnostic string.
- Fallback representations may include an object's memory address, so they can be unstable across runs and unsuitable for snapshots or durable serialization.
Example: Inspect a value representation
value = {"name": "Ada", "roles": ["admin", "developer"]}
text = repr(value)
print(text)
print(eval(text) == value)Creates a printable representation of a dictionary, then demonstrates that this representation can be evaluated back to an equal value for this built-in type.
When to use it
Round-trip inspection
Checking whether a built-in value has a reconstructible representation
Class-controlled representations
Implementing custom object diagnostics
Interview questions
QWhat does Python's repr() function return?
repr(object) returns a string containing a printable representation of the object. For many types, the representation is intended to produce an equal-valued object when passed to eval().
Follow-up: Can every repr() result be passed to eval()? No; the documentation explicitly describes angle-bracket fallback representations for cases where reconstruction is not available.
QWhat are the input and output of repr()?
The function accepts one object argument and returns a string. The result is representation text, not the original object itself.
Follow-up: How can a class influence this output? It can define a method controlling what repr() returns for its instances.
QHow can a class customize repr() for its instances?
A type can control the representation of its instances by defining a method. This lets custom objects provide their own printable representation.
Follow-up: What should a custom representation avoid? It should avoid implying reliable reconstruction unless the representation actually supports that use.
Related
strasciireprlib