Python File Operation

File handling is one of the important operations that a programming language provides.

What is a file?

The file provides a storage mechanism in a program to store our data. It is a named location on disk that can store our information which is stored permanently in the hard disk. As our program is executed in Random Access Memory (RAM), it loses its data in variables when the program exists.

File operation takes place in three stages in Python:-

1. Open a file
2. Perform operation ( read or write )
3. Close the file

How to open a file in Python?

Python provides open() function that helps to open a file in various modes. The function returns a file object which can be used to perform various operations like reading, writing, etc.

The syntax to use the open() function is given below.

Let us have a look at an example,

# opens the file hello.txt in read mode 
file_obj = open("hello.txt", "r")

if file_obj:
    print("File is opened successfully")

For this to be error-free, we need a hello.txt file to be created in the same folder where the program is written.

It is always good practice to include encoding while dealing with files,

How to close a file Using Python?

Once the file operations are completed, we require to close the file in order to free up memory space.

The syntax to use the close() method is given below.

# opens the file hello.txt in read mode
file_obj = open("hello.txt", "r")

if file_obj:
    print("File is opened successfully")
    
file_obj.close()

try:
   f = open("hello.txt",encoding = 'utf-8')
   # perform file operations
finally:
   f.close()

with open("hello.txt",encoding = 'utf-8') as f:
   # perform file operations

fo = open("hello.txt", "wb")
print("Name of the file: ", fo.name)
print("Closed or not : ", fo.closed)
print("Opening mode : ", fo.mode)

fo = open("hello.txt", "wb")
print("Name of the file: ", fo.name)
print("Closed or not : ", fo.closed)
print("Opening mode : ", fo.mode)

with open("hello.txt", 'w', encoding ='utf-8') as f:
   f.write("Welcome to Programming World.\n")
   f.write("This is a file operation.\n")
   f.write("It contains three lines.\n")

How to read a file in Python?

We can use read(size) function to read from the file where size is the number of characters to be read from the file. If the size is not defined, it reads all the data.

f = open("hello.txt", 'r', encoding = 'utf-8')
print("### Read first 7 characters from hello.txt")
print(f.read(7))

print("\n### Read rest of the contents")
print(f.read())

f.seek(0)
print("\n### Read all of the contents")
print(f.read())

f.close()

The output of the above program is:-

To Loop through lines in a file, we can use for loop.

f = open("hello.txt", 'r', encoding = 'utf-8')
for line in f:
    print(line, end = '')

f.close()

Similarly, we can use readline() function to read line by line. The readlines() function will output the list of lines that can be iterated to get the contents.

What are File Methods provided by Python?