Reading Files in Python

Learn how to open a file, read its contents and process file data using different Python methods.

What is Reading a File?

Reading a file means getting the data stored inside a file and using that data in a Python program.

Python provides the open() function to open a file and different methods to read its contents.

Reading File Diagram

The basic process of reading a file is:

Step 1: Open a File

To read a text file, we can open it using open() with "r" mode.

file = open("example.txt", "r")

Here:

• example.txt is the file name.
• "r" means read mode.
• file stores the opened file object.

Step 2: Read the Complete File

The read() method reads the file content.

file = open("example.txt", "r")

data = file.read()

print(data)

file.close()

Suppose example.txt contains:

Hello Python
Welcome to File Handling

Output:

Hello Python
Welcome to File Handling

The complete file content is returned as one string.

Reading a File Using with

A better and safer way is to use the with statement.

with open("example.txt", "r") as file:

    data = file.read()

    print(data)

When the with block finishes, Python handles the file resource automatically.

Reading a Specific Number of Characters

We can pass a number to read() to read only a specific number of characters.

with open("example.txt", "r") as file:

    data = file.read(5)

    print(data)

If the file starts with:

Hello Python

Output:

Hello

Here, only the first five characters are read.

Reading One Line Using readline()

The readline() method reads one line from the file.

with open("example.txt", "r") as file:

    line = file.readline()

    print(line)

Suppose the file contains:

Python
Java
.NET

The first call to readline() reads:

Python

Reading Multiple Lines

We can call readline() multiple times.

with open("example.txt", "r") as file:

    line1 = file.readline()
    line2 = file.readline()

    print(line1)
    print(line2)

Each call moves the reading position to the next line.

Reading All Lines Using readlines()

The readlines() method reads all lines and returns them as a list.

with open("example.txt", "r") as file:

    lines = file.readlines()

    print(lines)

For a file containing:

Python
Java
.NET

The result is similar to:

['Python\n', 'Java\n', '.NET']

Each item in the list represents a line.

Reading a File Line by Line Using a Loop

We can directly loop through a file object.

with open("example.txt", "r") as file:

    for line in file:

        print(line.strip())

This is useful when a file contains many lines and we want to process them one by one.

Using strip() While Reading

Lines read from a text file often contain a newline character.

We can use strip() to remove unwanted spaces and newline characters.

with open("example.txt", "r") as file:

    for line in file:

        print(line.strip())

Handling File Not Found Error

If the file does not exist, Python can raise a FileNotFoundError.

try:

    with open("example.txt", "r") as file:

        data = file.read()

        print(data)

except FileNotFoundError:

    print("File not found")

This prevents the program from stopping unexpectedly when the required file is missing.

Reading a File with Encoding

We can specify the text encoding while opening a file.

with open(
    "example.txt",
    "r",
    encoding="utf-8"
) as file:

    data = file.read()

    print(data)

UTF-8 is a common text encoding and is useful when working with multilingual text.

Understanding the File Position

Python keeps track of the current position while reading a file.

with open("example.txt", "r") as file:

    print(file.tell())

    file.read(5)

    print(file.tell())

The tell() method returns the current position in the file.

Moving the File Position with seek()

The seek() method changes the current reading position.

with open("example.txt", "r") as file:

    print(file.read(5))

    file.seek(0)

    print(file.read(5))

Here seek(0) moves the reading position back to the beginning of the file.

Reading a Text File

Example file:

students.txt

Rahul
Priya
Amit
Sneha

Python program:

with open("students.txt", "r") as file:

    for student in file:

        print(student.strip())

Output:

Rahul
Priya
Amit
Sneha

Store File Data in a List

We can store each line inside a Python list.

students = []

with open("students.txt", "r") as file:

    for line in file:

        students.append(line.strip())


print(students)

Output:

['Rahul', 'Priya', 'Amit', 'Sneha']

Count Number of Lines

count = 0

with open("students.txt", "r") as file:

    for line in file:

        count += 1


print("Total Lines:", count)

Output for the example file:

Total Lines: 4

Search for Text in a File

We can check whether a particular word exists in a file.

search_name = "Rahul"

with open("students.txt", "r") as file:

    data = file.read()

    if search_name in data:

        print("Student found")

    else:

        print("Student not found")

Output:

Student found

read() vs readline() vs readlines()

Best Practice for Reading Files

Common Mistakes

• Giving an incorrect file path.
• Forgetting to use read mode when needed.
• Trying to read a file that does not exist.
• Forgetting that read() returns a string.
• Forgetting to remove newline characters while processing individual lines.

Practice Programs

1. Create a file named students.txt containing five student names.
2. Read and display the complete file.
3. Read only the first line.
4. Read all lines using readlines().
5. Print every line using a for loop.
6. Count the total number of lines.
7. Search for a specific student name in the file.