Copy List in Python

In Python, when you want to duplicate a list, it's important to create a new list rather than simply creating a reference to the original list. If you assign one list to another using the assignment operator, any changes made to one list will affect the other. This lesson will cover different methods to copy lists properly.

1. Understanding List References

When you copy a list with an assignment, like this:

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list2 = list1

list2 becomes a reference to list1. This means any changes made to list1 will also be reflected in list2, and vice versa. To avoid this, you need to create an actual copy of the list.

2. Copying a List Using the copy() Method

Python provides a built-in method called copy() specifically for copying lists. This method creates a shallow copy of the list.

Example: Using the copy() Method

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thislist = ["apple", "banana", "cherry"]
mylist = thislist.copy()  # Making a copy of thislist
print(mylist)  # Output: ['apple', 'banana', 'cherry']

3. Copying a List Using the list() Method

Another way to copy a list is by using the built-in list() constructor. This method also creates a shallow copy of the list.

Example: Using the list() Method

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thislist = ["apple", "banana", "cherry"]
mylist = list(thislist)  # Making a copy using the list() method
print(mylist)  # Output: ['apple', 'banana', 'cherry']

4. Copying a List Using the Slice Operator

You can also create a copy of a list using the slice operator [:]. This method is concise and effective for duplicating a list.

Example: Using the Slice Operator

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thislist = ["apple", "banana", "cherry"]
mylist = thislist[:]  # Making a copy using the slice operator
print(mylist)  # Output: ['apple', 'banana', 'cherry']