If you are using python3, use the list’s copy() method. If you are using python2, you can copy a list by slicing or by using the list() function. Using this method, you will be able to fetch certain contents of the list. You can use this method when you want to change a list, but also keep a copy of the list. You can achieve this using the slice () method. The only downside is that it is not available in python2.īut if you are using python3, there is no debate this is the best, and most readable way to copy a list. Another method for cloning the elements of a list is by using the slicing technique. Python3 introduced a new method to lists called copy() and it does exactly what you think it does. Before you can truly understand the copy() method in Python, you must understand the concept of a shallow copy. Although the syntax is similar (I imagine by design), these are two different operations. 2) slice assignment: a0:2 b This replaces the slice of a with the contents of b. This is when Python3 comes to the rescue with a beautiful way to copy a list. This makes a copy of the slice of a and assigns it to b. > a = Įven though this is not a common way to copy a list, it is still a valid one. The slice () method can be used to create a copy of an array or return a portion of an array. This particular article aims at demonstrating the copy method. Python in its language offers a number of ways to achieve this. Sometimes, there is a need to reuse any object, hence copy methods are always of great utility. > s = "hello"īut since a list is an iterable itself, there is nothing that prevents you from creating a list from another list. Python List Copy () methods return a shallow copy of a list (returns a new list without modifying the original lists). The list() function is used to create a list object from any iterable.Īnd most of the time in real code, this iterable is not a list.įor example, the following code creates a new list off of the items of a string. Second: Copying using list() functionĪnother way to create a copy of a list is to use the list() built-in function. > a = Īs you can see, after a was modified, b remains unchanged.Īwesome, we successfully copied a python list. If b remains unchanged, then a and b refer to two separate objects. If b is modified, then a and b refer to the same object. Let’s try to modify a and see if b remains unchanged. Otherwise, they refer to different objects. Needless to say, two variables will refer to the same object only if the id of these two variable are exactly the same. If you don’t know what the id() function does, it basically returns the address of a python object in the memory. One way is by observing that id(a) is different from id(b). > a = ġ- the items of list b are the same as those of list a When you omit the start index and the end index from the slice, then your slice will start from the beginning of the list all the way to the end of the list.Īnd because slicing creates a new object, then the above code effectively copies or clones the whole list into another list. If you have been coding in python for a while, you probably came across some code that looks like this. The most common way (especially in python2) to copy a python list is to use slicing. The first two methods can be used in python2 and python3 whereas the third one works for python3 only. In this article, we will discuss three different methods to copy a python list. The following figure shows what we want to achieve when we copy or clone a list. Now if you wanted to add copy's of the last two elements, you could do the following: extendelements epcopy (i) for i in li -2: li.extend (extendelements) Please refer to Python's copy module doc for copy operations. > a = 10Īs you can see, changing the value of a also changes the value of b because they both refer to the same list object.Ĭopying a python list means creating a new python object whose contents are identical. This means that making changes to the last two objects in the list will also change the objects at index 2 and 3. Let’s check what happens to b when we modify a. Let’s take a look at this example > a = ī is in fact a, they both refer to the same python object. We can use it to copy complete list while creating a new list i.e. Using namespace System::Collections::Generic Ĭonsole::WriteLine("\nCapacity: ", dinosaurs.Capacity)Ĭonsole.WriteLine(vbLf
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