Copying makes a new object with the same elements as the original. Unlike an alias, which points to the same object, a copy can be changed without changing the original. section 28.0 section 28.2
For lists, you can make a copy in several ways:
- Create a new list from an existing one with list(original). section 28.2
- Call original.copy() to create a separate list with the same elements. section 28.2
- Use sorted(original) to get a sorted list while leaving the original unchanged. section 28.2
artists = ["monet", "picasso"]
painters = artists.copy()
painters.append("van gogh")
painters
Out[24]: ["monet", "picasso", "van gogh"]
artists
Out[25]: ["monet", "picasso"]
Appending to painters changes the copied list, while artists stays unchanged. section 28.2
A copy is also useful when you need to iterate over one list while changing another. For example, a stack can return a copy of its internal list so callers cannot mutate that stored list through the returned value. section 28.2 section 32.1
