4 methods for Writing a list to a file in Python

Writing lines to a file in python is quite simple and easy, but is it also true for writing lists to a file.

Let’s see.

In this article, we will see about all the different methods about how to write a list onto a file in python.

While working with files in python, we need to take care of a few things.

1. Before writing to a file, we have to first open the file using open() with write mode w parameter.
2. We can write on to a file using either write() or writelines()
3. Most importantly, we have to close the file using close()

Method 1: Using the for loop #

This is again one of the many use cases of the for loop.

The mighty for loop is capable of solving many of the problems in python.

For writing a list to a file in python, we have to use both the for loop and the write() method.

By this we can imply iterate through a list of strings and by the help of the write() method, write each iteration to the file.

lines = ['Hello','World', 'Welcome to Python.shiksha']
path = "E:/Sample Folder/test.txt"
f=open(path,'w')
for i in lines:
    f.write(i+'\n')

f.close()

This is a very beginner method of solving this problem i.e. good and effective for novice coders.

But if you are not a beginner, you might not be interested in the same.

Let’s see the other methods.

Method 2: Using the string.join() method #

Since, python is a very versatile language, it has a lot of inbuilt methods to work on with, thus there is also a string method that we can use in order to write a list to a file.

Instead of a for loop we can use the join() method, by the help of which we can join the whole list using a delimiter and forming one super string and then we can use the write() method to add the super string onto our file.

lines = ['Hello','World', 'Welcome to Python.shiksha']
path = "E:/Sample Folder/test.txt"
f=open(path,'w')
string='\n'.join(lines)
f.write(string)

f.close()

Thus pretty easily by using the join() method we wrote a list to a file.

But can we make this code a little bit more compact?

Yes, we can.

Method 3: Using string.join() with open() method #

In the previous section, we saw about the join() method but can we make that code more compact.

Yes, of course we can, by making the opening of the file using open() method and using the string.join() method directly.

lines = ['Hello','World', 'Welcome to Python.shiksha']
path = "E:/Sample Folder/test.txt"
with open(path,'w') as f:
  f.write('\n'.join(lines))

Method 4: Using the writelines() method #

Previously we saw the use of the write() method, which takes in a string as an argument and writes it onto a file.

But files in python also have a writelines() method which takes in a list of strings as the argument and writes the list onto a file.

We can directly use the list but in order to make our text look better and cleaner, firstly we need to append the newline character after every line by using the map() function.

lines = ['Hello','World', 'Welcome to Python.shiksha']
path = "E:/Sample Folder/test.txt"
f=open(path,'w')
lines=map(lambda x:x+'\n', lines)
f.writelines(lines)
f.close()

I am using lamba function append new line to every element in a list.

Conclusion #

In this article, we discussed in detail about the various methods that we can use in order to write a list to a file in python.

We started our discussion from the beginner approach i.e. a for loop and later extended it to the inbuilt join() method followed by its compact version and then finally concluding with the programmer approach i.e. the writelines() method.

I am Dibyanshu Mohanty, Undergraduate Engineering Student at VIT, Vellore with a keen interest in Web and App Development

https://python.shiksha/authors/dmohanty/