copy_deepcopy

Copy & Deepcopy

Assignment creates an alias. copy.copy() is shallow. copy.deepcopy() is fully independent.

Files

File	Description
example.py	Shallow vs deep, assignment, cyclic structures

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Descriptive Example

Scenario

Copy a nested list — shallow copy shares inner lists, deep copy does not.

import copy

original = [[1, 2], [3, 4]]
shallow = copy.copy(original)
deep = copy.deepcopy(original)

original[0].append(99)

print(original)   # [[1, 2, 99], [3, 4]]
print(shallow)    # [[1, 2, 99], [3, 4]]  ← inner list shared!
print(deep)       # [[1, 2], [3, 4]]      ← unaffected

Assignment vs copy

a = [1, 2, 3]
alias = a           # same object
copied = a.copy()   # new outer list

a.append(4)
print(alias)    # [1, 2, 3, 4] — alias sees change
print(copied)   # [1, 2, 3]    — independent

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Interview Q&A

Q1: What is the difference between shallow and deep copy?
A: Shallow copy creates a new outer container but inner objects are shared. Deep copy recursively copies everything into fully independent objects.

Q2: When do you need deepcopy?
A: When you need complete independence — nested mutables, graphs, or when downstream code might mutate nested structures.

Q3: Does list.copy() perform a deep copy?
A: No. list.copy() and copy.copy() are both shallow. Use copy.deepcopy() for nested independence.

Q4: What about copying objects with circular references?
A: deepcopy handles cycles by tracking already-copied objects. Manual recursion would infinite-loop without this.

Q5: Copy vs pickle for cloning objects?
A: Pickle serializes/deserializes — also creates a copy but slower and has security implications with untrusted data.

Q6: When is shallow copy sufficient?
A: Flat lists, immutable contents, or when you intentionally want shared inner objects (e.g., shared config reference).

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Run

python3 example.py