Working with Files - Reading

Why Read Files?

Programs often need to work with data stored in files. Think about reading a list of names from a text file, loading configuration settings, or processing a data file.

Reading files lets your program access information that was saved earlier or created by other programs.

Common uses:

• Read configuration settings
• Load user data
• Process text documents
• Read CSV data files
• Load saved game progress

Opening a File

To read a file, you first need to open it using the open() function.

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

What this does: Opens data.txt file in read mode. The "r" means read-only.

Important: Always close the file when done.

file.close()

Reading Entire File

The easiest way to read a file is using the read() method.

file = open("data.txt", "r")
content = file.read()
print(content)
file.close()

What happens: Reads everything from the file and stores it in the content variable as one big string.

Better Way - Using with Statement

The with statement automatically closes the file, even if something goes wrong.

with open("data.txt", "r") as file:
    content = file.read()
    print(content)

Why this is better:

• No need to remember file.close()
• File closes automatically when done
• File closes even if there's an error
• This is the recommended way

From now on, we'll use with statement in all examples.

Reading Line by Line

Often you want to process one line at a time instead of reading everything.

Using readline()

with open("data.txt", "r") as file:
    line1 = file.readline()
    line2 = file.readline()
    print(line1)
    print(line2)

What happens: Each readline() reads one line and moves to the next line.

Using readlines()

with open("data.txt", "r") as file:
    lines = file.readlines()
    print(lines)

What this returns: A list where each item is one line from the file.

Example result: ['First line\n', 'Second line\n', 'Third line\n']

Notice: Each line includes \n (newline character) at the end.

Looping Through Lines

This is the most common and efficient way to read files.

with open("data.txt", "r") as file:
    for line in file:
        print(line)

What happens: Reads one line at a time in the loop. Memory efficient for large files.

Cleaning Up Lines

Lines from files often have extra whitespace or newline characters. Use strip() to clean them.

with open("data.txt", "r") as file:
    for line in file:
        clean_line = line.strip()
        print(clean_line)

What strip() does: Removes whitespace (spaces, tabs, newlines) from both ends of the string.

Handling File Errors

What if the file doesn't exist? Your program will crash unless you handle the error.

try:
    with open("data.txt", "r") as file:
        content = file.read()
        print(content)
except FileNotFoundError:
    print("File not found")

What this does: If file doesn't exist, instead of crashing, it prints "File not found".

Reading Specific Number of Characters

You can read a specific number of characters instead of everything.

with open("data.txt", "r") as file:
    first_10 = file.read(10)
    print(first_10)

What happens: Reads only the first 10 characters from the file.

Checking File Position

When you read from a file, Python keeps track of where you are.

with open("data.txt", "r") as file:
    print(file.tell())
    file.read(10)
    print(file.tell())

What tell() does: Shows current position in the file (number of characters read so far).

Moving Position

You can move to a specific position using seek().

with open("data.txt", "r") as file:
    file.read(10)
    file.seek(0)
    content = file.read()
    print(content)

What this does:

• Reads 10 characters
• seek(0) moves back to the beginning
• Reads entire file from start

Reading Different Encodings

Sometimes files use different character encodings. UTF-8 is the most common.

with open("data.txt", "r", encoding="utf-8") as file:
    content = file.read()
    print(content)

When you need this: Files with special characters or multiple languages.

Practice Example

The scenario: You have a file called students.txt with student names, one per line. You want to read and process them.

File content (students.txt):

Python program:

try:
    with open("students.txt", "r") as file:
        students = []

        for line in file:
            clean_name = line.strip()
            students.append(clean_name)

        print("Total students:", len(students))
        print("First student:", students[0])
        print("All students:")

        for i, student in enumerate(students, 1):
            print(str(i) + ".", student)

except FileNotFoundError:
    print("Student file not found")

What this program does:

1. Opens students.txt safely with error handling
2. Creates empty list for students
3. Reads each line and removes extra whitespace
4. Adds each cleaned name to list
5. Prints total count
6. Shows first student
7. Lists all students with numbers

Reading CSV-like Data

If your file has comma-separated values, you can split each line.

File content (data.txt):

Python program:

with open("data.txt", "r") as file:
    for line in file:
        clean_line = line.strip()
        parts = clean_line.split(",")
        name = parts[0]
        age = parts[1]
        job = parts[2]
        print("Name:", name, "Age:", age, "Job:", job)

What split() does: Breaks the line at each comma, creating a list of parts.

Key Points to Remember

Use open() with "r" mode to read files. Always use with statement so files close automatically.

read() gets entire file, readline() gets one line, readlines() gets all lines as a list.

Loop through file directly with "for line in file" - this is memory efficient for large files.

Use strip() to remove extra whitespace and newline characters from lines.

Use try-except with FileNotFoundError to handle missing files gracefully without crashing.

Common Mistakes

Mistake 1: Forgetting to close file

file = open("data.txt", "r")
content = file.read()
# Forgot file.close()!

Fix: Use with statement instead.

Mistake 2: Reading file twice

with open("data.txt", "r") as file:
    content1 = file.read()
    content2 = file.read()  # This will be empty!

After reading once, you're at the end. Use seek(0) to go back.

Mistake 3: Wrong file path

file = open("documents/data.txt", "r")  # File might not be here

Always check the file path is correct relative to your program.

Mistake 4: Not handling newlines

with open("data.txt", "r") as file:
    for line in file:
        print(line)  # This has double spacing!

Fix:

print(line.strip())

What's Next?

Now you know how to read files. Next, you'll learn about writing files - creating new files, adding content, and updating existing files.