How to append list to list python

Python: How to append list values into the list properly?

I want to add the values of temp list into the main list. I tried to add some values into the temp list and then append the temp list into the main list as following, but it shows always latest values in the main list.

My expectation is:

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to your original code you will see [[3, 4, 5, 99], [3, 4, 5, 99]] as answer.

You’re looking for the extend method.

You need to assign temp[]=[] rather than temp[:]=[]

Pretty much nothing in Python makes a copy unless it explicitly says it makes a copy. In particular, append doesn’t make a copy; any changes to the object you append will be reflected in the list you appended it to, because the list is holding a reference to the original object.

To avoid problems like this, don’t clear out an existing object when you want a new one. Instead, create a new object:

I suppose if you really want to clear the original temp list instead of replacing it, you could instead make a copy when you append:

How to Append to Lists in Python – 4 Easy Methods!

Lists are an incredibly useful feature in Python! In this post, we’ll explore how to append to lists in Python. We’ll cover this off in more detail in the post below, but here’s a quick overview of how to append to lists in Python.

The Quick Answer:

Table of Contents

A Quick Overview of Lists in Python

Lists in Python are mutable, meaning they can be changed after being defined. They can also contain different data types, including strings, integers, floats, and even other lists!

To given an example of this, let’s create a list and access its first and its last item:

If you want to check out our tutorial on List Comprehensions, check out this link.

Append to Lists in Python

The append() method adds a single item to the end of an existing list in Python. The method takes a single parameter and adds it to the end. The added item can include numbers, strings, lists, or dictionaries. Let’s try this out with a number of examples.

Appending a Single Value to a List

Let’s add a single value to a list:

Appending to List to a List

You’ll notice that the output’s fourth item is a separate list. If we tried to access the fourth item, we would output a list:

If we wanted to access the number 4 – the first value of the fourth item of sample_list – we would have to write the following code:

Insert to List in Python

While the append method will always add an item to the end of a list, we can define where we would want an item added using the insert method.

The insert method takes two parameters:

Let’s try this out with an example:

Extend List in Python

The third method to add to a list in Python is to extend a list using the Extend() method. The extend method works quite similar to the append method, but it adds all items of another iterable item, such as a list or a tuple. If we had tried this with the append method, it would have inserted the whole list as an item in itself.

Let’s try this out with an example:

This also works well with tuples:

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Concatenate List in Python

List concatenation works quite similar to the extend method, but uses an operator instead of a method to accomplish the same for multiple lists. Let’s try this out with an example:

We could also re-write this in Pythonic shorthand:

Conclusion: How to Append to Lists in Python

In this post, we explored multiple ways to add to lists in Python, including the append, insert, and extend methods. If you have any further questions about the methods, leave a comment or check out the official documentation for append(), insert(), and extend().

Did We Mention We Have an eBook?

To learn more about related topics, check out the tutorials below:

Append to a List in Python

In this article, we’ll take a look at how we can append to a List in Python.

Python’s list.append() provides the solution to this, so we’ll see some examples using this method.

Let’s get started!

Append to a normal List in Python

We can use Python’s built-in append() method on our List, and add our element to the end of the list.

Output

As you can observe, our list has the two elements 10 and “Hello” inserted at the end. This is the case when you’re appending to a normal list.

Let’s now look at some other cases now.

Append to a List in Python – Nested Lists

A Nested List is a List that contains another list(s) inside it. In this scenario, we will find out how we can append to a list in Python when the lists are nested.

We’ll look at a particular case when the nested list has N lists of different lengths. We want to insert another list of exactly N elements into our original list.

But now, instead of directly appending to the nested list, we’ll be appending each of the N elements to each of the N lists, in order.

To show you an example, here’s our nested list having N = 3 lists:

We’ll insert each of the N elements of the list:

10 will be appended to the first list, 11 to the second, and 12 to the third.

So, our output will be:

Got the problem? Let’s solve it now!

Output

Indeed, our output matches what we expected!

Conclusion

In this article, we learned how we could append to a Python List, and examined various cases for this process.

How to append multiple values to a list in Python

I am trying to figure out how to append multiple values to a list in Python. I know there are few methods to do so, such as manually input the values, or put the append operation in a for loop, or the append and extend functions.

However, I wonder if there is a more neat way to do so? Maybe a certain package or function?

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You can use the sequence method list.extend to extend the list by multiple values from any kind of iterable, being it another list or any other thing that provides a sequence of values.

So you can use list.append() to append a single value, and list.extend() to append multiple values.

Other than the append function, if by «multiple values» you mean another list, you can simply concatenate them like so.

There’s also itertools.chain if you are more interested in efficient iteration than ending up with a fully populated data structure.

if the number of items was saved in a variable say n. you can use list comprehension and plus sign for list expansion.

I can’t add a comment, but I can’t be silent either if the number of items was saved in a variable say n. you can use list comprehension and plus sign for list expansion.

Here we are inserting a list to the existing list by creating a variable new_values.

Note that we are inserting the values in the second index, i.e. a[2]

But here insert() method will append the values as a list.

So here goes another way of doing the same thing, but this time, we’ll actually insert the values in between the items.

Python List append() Method

How can you add more elements to a given list? Use the append() method in Python. This tutorial shows you everything you need to know to help you master an essential method of the most fundamental container data type in the Python programming language.

Definition and Usage

Here’s a short example:

Related articles:

Syntax

You can call this method on each list object in Python. Here’s the syntax:

Arguments

Code Puzzle

Now you know the basics. Let’s deepen your understanding with a short code puzzle—can you solve it?

You can check out the solution on the Finxter app. (I know it’s tricky!)

Here’s your free PDF cheat sheet showing you all Python list methods on one simple page. Click the image to download the high-resolution PDF file, print it, and post it to your office wall:

Examples

Let’s dive into a few more examples:

You can see that the append() method also allows for other objects. But be careful: you cannot append multiple elements in one method call. This will only add one new element (even if this new element is a list by itself). Instead, to add multiple elements to your list, you need to call the append() method multiple times.

Python List append() At The Beginning

What if you want to use the append() method at the beginning: you want to “append” an element just before the first element of the list.

Well, you should work on your terminology for starters. But if you insist, you can use the insert() method instead.

Here’s an example:

Python List append() Multiple or All Elements

The answer is no—you cannot append multiple elements to a list by using the append() method. But you can use another method: the extend() method:

You call the extend() method on a list object. It takes an iterable as an input argument. Then, it adds all elements of the iterable to the list, in the order of their occurrence.

Python List append() vs extend()

I shot a small video explaining the difference and which method is faster, too:

The difference between append() and extend() is that the former adds only one element and the latter adds a collection of elements to the list.

You can see this in the following example:

In the code, you first add integer elements 1 and 2 to the list using two calls to the append() method. Then, you use the extend method to add the three elements 3, 4, and 5 in a single call of the extend() method.

Which method is faster — extend() vs append()?

To answer this question, I’ve written a short script that tests the runtime performance of creating large lists of increasing sizes using the extend() and the append() methods.

Our thesis is that the extend() method should be faster for larger list sizes because Python can append elements to a list in a batch rather than by calling the same method again and again.

I used my notebook with an Intel(R) Core(TM) i7-8565U 1.8GHz processor (with Turbo Boost up to 4.6 GHz) and 8 GB of RAM.

The code consists of three high-level parts:

Here’s the resulting plot that compares the runtime of the two methods append() vs extend(). On the x axis, you can see the list size from 0 to 1,000,000 elements. On the y axis, you can see the runtime in seconds needed to execute the respective functions.

The resulting plot shows that both methods are extremely fast for a few tens of thousands of elements. In fact, they are so fast that the time() function of the time module cannot capture the elapsed time.

But as you increase the size of the lists to hundreds of thousands of elements, the extend() method starts to win:

For large lists with one million elements, the runtime of the extend() method is 60% faster than the runtime of the append() method.

The reason is the already mentioned batching of individual append operations.

However, the effect only plays out for very large lists. For small lists, you can choose either method. Well, for clarity of your code, it would still make sense to prefer extend() over append() if you need to add a bunch of elements rather than only a single element.

Python List append() vs insert()

The difference between the append() and the insert() method is the following:

Here’s an example showing both append() and insert() methods in action:

Both methods help you add new elements to the list. But you may ask:

Which is faster, append() or insert()?

All things being equal, the append() method is significantly faster than the insert() method.

Here’s a small script that shows that the append() method has a huge performance advantage over the insert() method when creating a list with 100,000 elements.

The experiments were performed on my notebook with an Intel(R) Core(TM) i7-8565U 1.8GHz processor (with Turbo Boost up to 4.6 GHz) and 8 GB of RAM.

Python List append() vs concatenate

So you have two or more lists and you want to glue them together. This is called list concatenation. How can you do that?