File Operations in Python

1. File Handling

Files are used to store the data permanently. These are basically used to store the information. Files stores data permanently in non-volatile memory like a hard disk. Different file operations in python are:

• Opening a file.
• Reading from a file.
• Writing to the file.
• Closing a file.

Opening a file.

we can open a file using open() function either in read or in write mode. The open() function takes two parameters, filename and opening mode. After calling this function, if a given filename exists then this function will return that existing file object.

Syntax open(filename, mode)
The different modes available are:

• "r" for reading.
• "w" for writing.
• "a" for appending.
• "r+" for both reading and writing.
• "t" for opening a file in text mode.
• "b" for opening a file in binary mode.

Examples

>>>f=open("Hello.txt") #opens file in current directory.
>>>f=open("Hello.txt","r") #opens a existing file in read mode.
>>>f=open("Hello.txt","w") #opens a file in write mode,
                           # if there's no such named file
                           # then it will automatically create a
                           # new file and open it.

Writing to a file.

To write something to a file, we need to open a file write mode(w) or in append mode(a). Python provides the write() method to write text or sequence of bytes (i.e, binary file) to the file. When we open a file in 'w' mode, it will create a new file with a given filename if that named file does not exist else it will open that file overwriting all the content that means contents inside the file get erased.

Example

f=open('Hello.txt','w')
f.write("Hello, python!")
f.write("\nI love python.")
f.close()

This will create a file called Hello.txt where the following text will be written to.

    Hello, python!
    I love python.
    

Let us open this Hello.txt file in an append(a) mode.

with open('test.txt','a') as file:
    file.write("\nPython is awesome")
    file.write("\nPython is fun.")
    file.close()

This will append the sentences to the end of the file as follows:

Hello, python!
I love python.
Python is awesome
Python is fun

Reading from a File.

To read the file in python, we should open our file in read mode(r). There is a method called read() which takes the size of the data to be read as a parameter.

If the parameter is not passed, it will read all the remaining content to the end of the file.

Let us read the content from Hello.txt that we have created.

>>>file=open('Hello.txt','r')
>>>file.read(5) #reads first five characters from the file.
   'Hello'

>>>file.read(10) #reads next ten characters from the file.
   ', python!\n'

>>>file.read(30) #reads next 30 characters from the file.
   'I love python.\nPython is awesom'

>>>file.read() #reads entire remaining file content.
   'e\nPython is fun.'

In python, there is another method, called readline() which is used to read the individual lines from the file. i.e,

>>>file.readline()
   'Hello python!\n'
>>>file.readline()
   'I love python.\n'

>>>file.readline()
   'Python is awesome\n'

Also, readlines() method reads the entire remaining file content to the end of the file. i.e,

>>>file.readlines()
   [', Python is fun.']

Closing a file

After all the file operations are done, it is a good programming practice that we should always close a file. Closing a file in python is done using the close() method.

Example

file=open('Hello.txt')
file.close()

This is not the proper way to close a file. This way has no surety that the file will always be closed. If any exceptions occur, the program will be terminated without closing a file. So, a better way would be using exception handling.

try:
   file=open('Hello.txt')
finally:
   file.close()

Another way is to use the 'with' block. In this way, there's no need to close a file explicitly, it is done internally.

with open('Hello.txt','r') as file:
    # different file operations