Python Tutorial

Python Copy Lists

list2 = list1 copies the reference, not the data. Use copy(), list(), or a slice to get a real copy.

Wrong Copy

Both names point to the same list. Changing one changes the other.

thislist = ["apple", "banana", "cherry"]
list2 = thislist
list2.append("orange")
print(thislist)

copy(), list(), slice

Three ways to duplicate the items.

thislist = ["apple", "banana", "cherry"]
print(thislist.copy())
print(list(thislist))
print(thislist[:])

📘 Real-World Deep Dive

Most list "copies" are shallow and that's a frequent source of subtle bugs. Knowing when you need <code>list.copy</code>, <code>list(xs)</code>, slicing, and <code>copy.deepcopy</code> is the difference between correct code and silent aliasing.

Real-Life Scenario

Defensive deep-copy before a destructive operation; show what goes wrong with shallow copy on a list of dicts.

Real-Life Example

import copy

shared = [{"k": "v"}, {"k": "w"}]
shallow = shared.copy()                  # shares inner dicts
deep    = copy.deepcopy(shared)

print("shallow is shared:", shallow is shared)
print("shallow[0] is shared[0]:", shallow[0] is shared[0])
print("deep[0]    is shared[0]:", deep[0]  is shared[0])

shared[0]["k"] = "MUTATED"
print("after mutation:")
print(" shared  :", shared)
print(" shallow :", shallow)            # inner dict mutated!
print(" deep    :", deep)               # unchanged

Expected Output

shallow is shared: False
shallow[0] is shared[0]: True
deep[0]    is shared[0]: False
after mutation:
 shared  : [{'k': 'MUTATED'}, {'k': 'w'}]
 shallow : [{'k': 'MUTATED'}, {'k': 'w'}]
 deep    : [{'k': 'v'}, {'k': 'w'}]

Common mistakes

new = old_list aliases; new = list(old) and new = old[:] do shallow copies.
Mutable inner objects mean shallow copy doesn't isolate you from mutations.
deepcopy can recurse through arbitrary graphs; cap with depth or memo for big structures.

🚀 Performance & Best Practices

list.copy() is faster than copy.copy(list); list(xs) is competitive.
For lists of primitives, slice (xs[:]) and list(xs) are equally fast — pick the readable form.
Use copy.replace (Python 3.13+) on dataclasses instead of deepcopy.

🧪 Try It Yourself

Implement shallow_replace(items, predicate, replacement) that returns a brand-new outer list.
Profile deepcopy vs. JSON-roundtrip (json.loads(json.dumps(x))) for nested data.
Write a recursive deep_freeze that converts dicts/lists into tuples inside tuples.

FAQ: Python Copy Lists

Common questions about this page.

What is Python Copy Lists?

Python Copy Lists is a Python Tutorial lesson that explains copy list python in Python. list2 = list1 copies the reference, not the data. Use copy(), list(), or a slice to get a real copy. Copy the samples and run them in the Python editor. It is written for beginners who want a clear definition and working examples.

Should I run copy list python examples locally for better learning?

Yes. Use the browser editor on StudyGrid for a quick check, then Download the example and run it on your computer. Local runs show real errors and the real toolchain, which is one of the fastest ways to learn copy list python in this Python Tutorial Python lesson (Python Copy Lists).

How do I use copy list python in Python?

To use copy list python in Python, follow the examples on this StudyGrid page. Copy a snippet, run it in the browser, then Download and run it locally for better learning. Change the values and compare the output.

What is the syntax of copy list python?

This Python Copy Lists tutorial shows copy list python syntax with short Python examples. Use the code blocks in this lesson for the exact statements, then try them in your editor.

Python Copy Lists example for beginners

Yes. This page includes a beginner copy list python example you can copy and run. It is designed for searches such as "copy list python for beginners", "copy list python example", and "how to use copy list python".

What are common mistakes with copy list python?

Common copy list python mistakes include wrong syntax, mixing types, and skipping practice. Work through this Python Tutorial chapter in order, run every example, and check the output before moving on.

Why should I learn copy list python?

Python Copy Lists is used in real Python work. Learning copy list python helps you write clearer programs and continue the Python Tutorial tutorial on StudyGrid.

Is Python Copy Lists free to learn online?

Yes. You can learn copy list python free on StudyGrid (studygrid.in). This chapter is part of the Python Tutorial path and includes examples, syntax, and next-step links.