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What is the difference between shallow copy and deep copy in Python?

Python/Codingeasy0.5 min readPremium

**Shallow copy** (`copy.copy()`): New top-level object; nested objects are references. Mutating nested objects in the copy affects the original. **Deep copy** (`copy.deepcopy()`): Recursive copy of all nested objects; fully independent. **Why it matters**: Shallow copy is...

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Frequency
Low
Asked at 2 companies
Category
179
questions in Python/Coding
Difficulty Split
127E|24M|28H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
AltimetrikInfosys
Interview Pro Tip

Red Flag: Modifying a shallow-copied list of dicts and being surprised when the original changes. Pro-Move: 'I use shallow copy for config snapshots where nested refs are OK; deep copy only when I need full isolation, and I avoid it for large objects.'

Key Concepts Tested
python

Why This Question Matters

This easy-level Python/Coding question appears frequently in data engineering interviews at companies like Altimetrik, Infosys. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (python) will help you answer variations of this question confidently.

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Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.

Expert Answer
96 words

Shallow copy (copy.copy()): New top-level object; nested objects are references. Mutating nested objects in the copy affects the original. Deep copy (copy.deepcopy()): Recursive copy of all nested objects; fully independent. Why it matters: Shallow copy is cheaper but can cause subtle bugs when sharing nested structures. Scalability trade-off: Deep copy is O(total objects) and can be slow/hung on cycles without special handling. Cost implication: Deep copy of large structures (e.g., nested dicts) can be expensive; shallow copy is O(1) for nested refs. Use shallow for flat or intentionally shared structures; deep when you need full isolation.

The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations covering performance optimization and real-world examples.

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According to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 2 companies. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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