Working with Files#

This section is focused on how to read and write data from files and update a file.

In this chapter you will learn how to:

Open files
Read files
Write files
Append to files

open() function#

Before performing any operation on the file like reading or writing, first, we have to open that file. The key function for working with files in Python is the open() function. The open() function takes two parameters, filename/file-path, and mode. The default opening mode of a file is a read-only mode. There are four different methods (modes) for opening a file:

“r” - Read - Default mode. Opens a file for reading
“a” - Append - Opens a file for appending
“w” - Write - Opens a file for writing
“x” - Create - Creates the specified file
“b” - binary mode
“t” - text mode (default)
“+” - reading and writing

To open a file for reading it is enough to specify the name or full path of the file:

f = open("my_file.txt", "rt")

The code above is the same as:

f = open("my_file.txt")

Because "r" for read, and "t" for text are the default values, you do not need to specify them. If the file does not exist, you will get an error.

read() Function#

When we open a file without setting the mode argument, the default is to open the file in “read-only” mode. The open() function returns a file object, which has a read() method for reading the content of the file.

f = open("my_file.txt")  # file, located in the same folder
print(f.read())
f.close()  # always close the file when you are done

Hello! Welcome to the text file.
This file is for testing purposes only.

If the file is located in a different location, you will have to specify the file path. By default, the read() method returns the whole text as one big string, but we can return one line by using the readline() method.

f = open("my_file.txt")
print(f.readline())  # read the 1st line
print(f.readline())  # read the 2nd line
f.close()

Hello! Welcome to the text file.

This file is for testing purposes only.

The readlines() method will return all the lines in a file in the format of a list where each element is a line in the file with a \n character.

f = open("my_file.txt")
print(f.readlines())
f.close()

['Hello! Welcome to the text file.\n', 'This file is for testing purposes only.']

In Python read() method returns the whole text as a string, so you can use splitlines() method to splits a string into a list. The splitting is done at line breaks.

f = open("my_file.txt")
output = f.read()
print(output.splitlines())
f.close()

['Hello! Welcome to the text file.', 'This file is for testing purposes only.']

Write and Create#

To write to an existing file, you must add a parameter to the open() function.

f = open("my_file.txt", "a") 
f.write("Now more content added to the file.\n")  # '\n' add a new line 
f.close()

f = open("my_file.txt")  # read the file after the append
print(f.read())
f.close()

Hello! Welcome to the text file.
This file is for testing purposes only.
Now more content added to the file.

f = open("my_file.txt", "w")  # the "w" method will overwrite the entire file
f.write("I have deleted the all content!")
f.close()

f = open("my_file.txt")  # read the file after the write
print(f.read())
f.close()

I have deleted the all content!

To create a new file in Python, use the open() method, with one of the following parameters:

“x” - create a file, returns an error if the file exists
“a” - create a file if the specified file does not exist
“w” - create a file if the specified file does not exist

A new empty file will be created.

f = open("myfile.txt", "x")

Create a new file if it does not exist:

f = open("myfile.txt", "w")

File and Context Manager#

The best way to open a file in Python is to use Python’s special with statement is known as a context manager. In this example, you want to open a file, and then the with statement, automatically closes the file.

with open('my_file.txt') as file:
    data = file.read()
    print(data)

Hello! Welcome to the text file.
This file is for testing purposes only.

Python’s for loop#

You can iterate over a file using Python’s for loop, this is actually one of the recommended methods for reading a file.

with open('my_file') as file:
    for line in file:
        print(line)

Hello! Welcome to the text file.

This file is for testing purposes only.

An alternative way to loop over the lines in a file.

with open('my_file') as file:
    lines = file.readlines()
    for line in lines:
        print(line)