Python add list to file

Python Program to Write List to File

In this Python tutorial, we will discuss how to write list to file in Python using different examples.

There are five methods to write a list to file in Python, which are shown below:

1. Using a for loop and the write() method
2. Using the writelines() method
3. Using the join() and the write() method
4. Using the JSON module
5. Using the pickle

How Python Write List to File

One common task is writing a list to a file, which can be useful for storing data that can be read later or for sharing data with other programs. There are several methods for writing a list to a file in Python, including using a for loop, the writelines () method, json module, etc.

Method-1: Python Write List to File using a for loop and the write() method

In this method, we use a for loop to iterate through each item in the list, and use the write() method to write each item to the file. We also add a newline character ‘\n’ after each item to write each item on a new line.

# create a list of numbers my_list = [1, 2, 3, 4, 5] # open a file named "output.txt" in write mode with open('output.txt', 'w') as f: # loop through the list and write each item to the file for item in my_list: f.write(str(item) + '\n') 

The code writes the elements of the list my_list to a file named output.txt, with each element on a new line. It uses the with statement to open the file in write mode and automatically close it after writing the data.

• The for loop iterates over each element in the list and writes it to the file as a string, followed by a newline character to create a new line for the next element.

Method-2: Python Write List to File using the writelines() method

In this method, we use the writelines() method to write each item in the list to the file.

# create a list of mobile phone brands mobile = ['samsung', 'redmi', 'oneplus'] # open a file named "f1.txt" in write mode file = open('f1.txt', 'w') # loop through the mobile phone list and write each item to the file for item in mobile: file.writelines([item]) # close the file file.close() 

The above code creates a list of mobile phone brands and then opens a file named “f1.txt” in write mode. It then loops through the list and writes each item to the file using the writelines() method. Finally, it closes the file.

Method-3: Python Write List to File using the join() and the write() method

In this method, we use the join() method to concatenate all the items in the list into a single string, separated by newline characters ‘\n’. We then use the write() method to write this string to the file.

# Define a list containing different types of values my_list = ["USA", 2, 3, 4, 5] # Open a file named 'join.txt' in write mode using a context manager # and write the contents of the list to the file in a specific format with open('join.txt', 'w') as f: f.write('\n'.join(map(str, my_list))) 

The above code defines a list called my_list containing various data types. It then uses the with a statement to open a new file called ‘join.txt’ in write mode and writes the contents of my_list to the file, with each element on a new line.

Method-4 Python Write List to File using the JSON module

In this method, we use the json module to write the list to a file in JSON format. We use the dump() method to write the list to the file in a JSON-encoded format.

# Import the json module, which provides an easy way to encode and decode JSON data import json # Define a list containing different types of values my_list = ["USA", 2, 3, 4, 5] # Open a file named 'output.json' in write mode using a context manager # and use the json.dump() function to write the contents of the list to the file in JSON format with open('output.json', 'w') as f: json.dump(my_list, f) 

The above code imports the json module, which provides functionality for working with JSON data. It defines a list called my_list containing various data types.

• It then uses the with statement to open a new file called ‘output.json’ in write mode and writes the contents of the list to the file in JSON format using the json.dump() function.

Method-5: Python Write List to File using the pickle

In this method, we use the pickle module to write the list to a file in a binary format. We use the dump() method to write the list to the file in a binary-encoded format.

# Import the pickle module, which provides an easy way to serialize and deserialize Python objects import pickle # Define a list containing different types of values my_list = ["USA", 2, 3, 4, 5] # Open a file named 'output.pkl' in write mode using a context manager and binary mode 'wb' # and use the pickle.dump() function to write the contents of the list to the file in binary format with open('output.pkl', 'wb') as f: pickle.dump(my_list, f) 

The above code imports the pickle module, It defines a list called my_list containing various data types.

• It then uses the with statement to open a new file called ‘output.pkl’ in write mode with binary mode ‘wb’, and writes the contents of the list to the file in binary format using the pickle.dump() function.

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Conclusion

In this tutorial, we learned how to write python list to file using the different methods:

• Using a for loop and the write() method
• Using the writelines() method
• Using the join() and the write() method
• Using the JSON module
• Using the pickle

I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.

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Python Program to Write List to File

The List in Python is a built-in data structure that stores heterogeneous or homogeneous data in a sequential form. Elements in a list may be unique or duplicates and are identified by a unique position called an index. Python writes list to file and saves the data contained in the list to a text file.

How to Write List to File in Python

The write() or writelines() method helps Python write lists to files. A list in Python can be written in a file in various ways. The basic steps include:

• Open a text file in write mode
• Write current items from the list into the text file
• Close the file after completing the write operation

Method 1: Using write()

The list is iterated using a loop, and during every iteration, the write() method writes an item from the list to the file along with a newline character.

1. Open a .txt file function in w mode (here w signifies write). The open() function shows the file path.
2. Next, create a list of items. Using a for loop to iterate through all the items in the list.
3. The write() function adds the list of items to the text file.
4. Close the file using the close() function.

Method 2: Using writelines()

The writelines() takes a list as its argument and writes all the elements of the list to a file. In the text file, the list elements are appended one after another without any space or newline characters.

1. Open a .txt file function in w mode (here w signifies write). The open() function shows the file path.
2. Create a list of items.
3. The writelines() function takes the list of items as its parameter and writes them in the text file.
4. Close the file using the close() function.

Method 3: Using String Join Along with «with open» syntax

The with open syntax automatically closes the file after executing all statements inside it. Thus, the close() function does not need to be called explicitly.

1. Create a list of items.
2. Open a .txt file function in w mode (here w signifies write). The open() function shows the file path.
3. The write function in this block adds the list of items to the text file.

Which is the Best Method to Write a List to File in Python?

The simplest solution for Python to write the list to a file is to use a file.write() method that writes all the items from the list to a file. The open() method opens the file in w mode. The list is looped through and all the items are written one by one.

FAQs

1. What does access mode ‘w’ mean?

The w mode refers to writing. It creates a new file if a file with the specified name is absent, else overwrites the existing file.

2. How many arguments does the open() function take?

The open() function takes two arguments the filename along with its complete path, and the access mode.

3. How many arguments does the close() function take?

The close() function doesn’t take any argument.

4. Why is using the with open() method not safe?

In the case of with open() , if some exception occurs while opening the file, then the code exits without closing the file.

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Conclusion

• Creating, reading, opening, writing, and closing files using Python comes under File Handling.
• Python write list to file can be implemented using multiple ways.
• write() method inserts a string to a single line in a text file.
• writelines() is used for inserting multiple strings from a list of strings to the text file simultaneously.
• No close() statement is required as with open syntax automatically closes the file after executing all statements inside it.

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Writing a List to a File in Python — A Step-by-Step Guide

In Python, a list is a common data type for storing multiple values in the same place for easy access. These values could be numbers, strings, or objects.

Sometimes, it’s useful to write the contents of a list to an external file.

To write a Python list to a file:

1. Open a new file.
2. Separate the list of strings by a new line.
3. Add the result to a text file.

Here is an example code that shows how to do it:

names = ["Alice", "Bob", "Charlie"] with open("example.txt", mode="w") as file: file.write("\n".join(names))

As a result, you should see a text file with the names separated by a line break.

Obviously, this is only one approach. If you are not satisfied with it, see the other examples below.

Write List to File As-Is

You cannot directly write a list to a file. But you can convert the list to a string, and then write it.

names = ["Alice", "Bob", "Charlie"] with open("example.txt", mode="w") as file: file.write(str(names))

As a result, you see a text file called example.txt with the following contents:

Write List to File Comma-Separated without Brackets

To write a list into a text file with comma-separated values without brackets, use string.join() method.

names = ["Alice", "Bob", "Charlie"] with open("example.txt", mode="w") as file: file.write(", ".join(names))

As a result, you see a text file called example.txt with the following contents:

Write Python List to File Tab-Delimited

Sometimes you might want to write the list contents into an external file by using tabs as separators between the values.

To do this, you need to use the string.join() method to join the list elements by using a tab as a separator.

names = ["Alice", "Bob", "Charlie"] with open("example.txt", mode="w") as file: file.write("\t".join(names))

The result is a file called example.txt with the following contents tab-separated:

Conclusion

Today you learned how to write a list to a file in Python.

To recap, all you need to do is open a file, separate the strings, and write them into the file. All this happens by using the native methods in Python in a couple of lines of code.

Thanks for reading. I hope you enjoy it.

Further Reading

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