L2 · Working engineerObject-oriented Python~4 min · 4 tests#76

str vs repr in Python

Implement __repr__ and __str__ on an Employee class so print() shows Employee(name='John', salary=50000). Learn which one Python calls when.

The problem

Make Employee(name, salary) print as:

Employee(name='John', salary=50000)

repr(employee) must return exactly that (note the quotes around the name — use !r)
str(employee) returns "John earns 50000"

Examples

Example 1

Input

repr(Employee("John", 50000))

Expected output

"Employee(name='John', salary=50000)"

Example 2

Input

str(Employee("John", 50000))

Expected output

'John earns 50000'

+ 2 hidden tests on Submit — containers use repr, f-strings use str.

Edge cases to ask about

Inside a list
f-strings

Hints

0/3

How an interviewer scores this

0/9

1. Understand the problemRestate it, ask about edge cases and input size.
2. Write a brute-force solutionCorrect first, clever later.
3. Get the correct outputautoAll visible examples pass.
4. Analyse time complexityautoCommit to a Big-O in the Complexity Lab.
5. Analyse space complexityautoExtra memory, not the input.
6. Identify the bottleneckautoMeasure your code — where does it bend?
7. OptimiseUsually: a set or dict instead of a scan.
8. Explain why it worksSay it out loud to Solvi.
9. Test the edge casesautoSubmit passes every hidden test.

Python 3.13 · Employee

class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

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Complexity Lab

What does this cost as n grows?

Interviewers score the analysis as much as the code. Commit to an answer first — then check it, and read why.

Time complexity of the optimal solution

Space complexity (extra memory)

Pick both to reveal the answer.

From brute force to optimal

The progression an interviewer wants to hear, one step at a time.

Approach	Time	Space	Idea
Two dunder methods	O(1)	O(1)	repr is for developers, str for users.

Walkthrough of the optimal approach (try it yourself first)

__repr__ is for developers: unambiguous, ideally valid Python that recreates the object. __str__ is for end users. print() and f-strings use __str__; containers, the REPL and debuggers use __repr__. If only __repr__ exists, str() falls back to it.

@dataclass generates a correct __repr__ for free.

Complexity: O(1) time, O(1) space. String formatting of two fields.

Reveal the reference solution

class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    def __repr__(self):
        return f"Employee(name={self.name!r}, salary={self.salary!r})"

    def __str__(self):
        return f"{self.name} earns {self.salary}"

Follow-ups interviewers ask

Rewrite it with @dataclass.
What does !r do in an f-string?

Frequently asked interview questions

Core interview concepts, complexities, and follow-ups scored by hiring teams.

What is the time complexity of __str__ vs __repr__ in Python?

The optimal solution runs in O(1) time and O(1) auxiliary space. String formatting of two fields.

What follow-up questions do interviewers ask about __str__ vs __repr__ in Python?

Rewrite it with @dataclass. What does !r do in an f-string?