In this article, we will learn how we can do File I/O operation in python. We briefly go through how to open a file, reading from it, writing into it, closing it and along with that various methods are available for file operations. File is a physical location on disk to store related information.

If we want to read from or write to a file first we need to open it and once done with our task we have to close it. So the operations can be as followed:

• Open a file
• Read/Write operation for file
• Close the file

How to Open A file in Python?

Python has a built-in read() function to open a file. This function returns the object of the file, it also called handle as it provides control for reading/modifying the file.

We can also specify mode in which we want to open a file. We can open a file in text mode('t') or binary mode('b'). We can also specify whether we want to read 'r', write 'w' or append 'a' to the file. The default is reading in text mode, we get strings when reading from the file. In python, unlike other languages character 'a' doesn't imply the ascii number 97 until it is encoded in ASCII. It is highly recommended to specify the encoding type while working with text files.

Example:

my_file = open("myfile.txt")      # equivalent to 'r' or 'rt'
my_file = open("myfile.txt",'w')  # write in text mode
my_file = open("temp_img.bmp",'r+b') # read and write in binary mode
my_file = open("myfile.txt",mode = 'r',encoding = 'utf-8') # opening a file in read mode for utf-8 encoded file

Below table lists all the possible modes and its description.

How to read files in Python?

Once the file is opened, there are various methods available for reading the file. read(size) method is used for reading size data, if not specified it will return the complete file.

my_file = open("test.txt",mode = 'r',encoding = 'utf-8')
print(myfile.read(10)) # reads only 10 characters
print(myfile.read()) # read complete file

We can read a file line by line using for loop and is also an efficient and fast way.

for line in myfile:
    print(line, end = '')

Now if we want to read file line by line, we can use readline() method. This method reads a file till the newline, including the newline character.

We can also change the current file cursor using the seek() method. The same way tell() method returns our current position as shown below:

myfile.tell() # This will return the cursor position
myfile.seek() # This will bring file cursor to its initial position

How to Write files in Python?

In order to write into a file in Python, we need to open it in write 'w', append 'a' or exclusive creation 'x' mode. The 'w' mode will overwrite into the file if it already exists so, we should take care when using it. Writing a stream to file is done using write() method.

with open("test.txt",'w',encoding = 'utf-8') as myfile:
   myfile.write("my first file\n")
   myfile.write("This file\n\n")
   myfile.write("contains three lines\n")

Python File Methods

There are various methods available with the file object. Some of them have been used in the above examples.

Here is the complete list of methods in text mode with a brief description.

That's it for file I/O operations.