Python list.copy Method: Usage and Examples

You want to edit a proposed shopping basket without immediately changing the original.

What You Need to Understand

list.copy() returns a shallow copy of a list. The new outer list has the same elements but is a different object.

When to Use It

You want to edit a proposed shopping basket without immediately changing the original.

Step-by-Step Python Example

basket = ["milk", "bread"]
proposed = basket.copy()
proposed.append("eggs")
print(basket)
print(proposed)

How the Example Works

The new entry appears only in proposed because the outer lists are independent.

Example Output

['milk', 'bread']
['milk', 'bread', 'eggs']
[[1, 9], [2]]

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

original = [[1], [2]]
shallow = original.copy()
original[0].append(9)
print(shallow)

Important Behavior and Edge Cases

For nested lists, copy() shares inner references. Use copy.deepcopy() only when independent nested data is necessary.

Try It Yourself

Copy a two-dimensional list and modify one inner list to observe shallow-copy behavior.

Common Beginner Mistakes

• For nested lists, copy() shares inner references. Use copy.deepcopy() only when independent nested data is necessary.
• Using the wrong collection method for this operation without checking whether it mutates the object, returns a result, or raises on missing data.

Key Takeaways

• list.copy() returns a shallow copy of a list.
• The new entry appears only in proposed because the outer lists are independent.
• For nested lists, copy() shares inner references.