Below is a FULL beginner-friendly Lesson 11, explaining File Handling in Python with clear explanations, examples, and outputs.
File handling is important because programs often store and read data from files.

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📘 Lesson 11: File Handling in Python

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🔹 1. What is File Handling?

File handling allows Python programs to:

✔ Read data from files
✔ Write data to files
✔ Store information permanently

Example uses:

• Saving user data
• Logging system activity
• Reading configuration files

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🔹 2. Opening a File

Python uses the open() function.

Syntax

file = open("filename", "mode")

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File Modes

Mode	Meaning
"r"	Read file
"w"	Write file (overwrites)
"a"	Append to file
"x"	Create new file
"b"	Binary mode

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🔹 3. Reading a File

Example 1: Read Entire File

Assume file data.txt contains:

Sameer
Ayesha
Saddam

Python Code

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

content = file.read()

print(content)

file.close()

Output

Sameer
Ayesha
Saddam

📌 Explanation

• "r" mode reads file
• read() reads entire content
• close() closes file

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🔹 4. Reading File Line by Line

Example 2

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

for line in file:
    print(line)

file.close()

Output

Sameer
Ayesha
Saddam

📌 Explanation
Loop reads each line one by one.

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🔹 5. Writing to a File

Example 3

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

file.write("Sameer\n")
file.write("Ayesha\n")

file.close()

📌 Explanation

• "w" mode overwrites existing file
• \n creates a new line

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File Content After Running

Sameer
Ayesha

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🔹 6. Appending to a File

Example 4

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

file.write("Saddam\n")

file.close()

File Content

Sameer
Ayesha
Saddam

📌 Explanation
"a" mode adds content without deleting old data

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🔹 7. Reading One Line

Example 5

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

line = file.readline()

print(line)

file.close()

Output

Sameer

📌 Explanation
readline() reads one line only

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🔹 8. Reading All Lines as List

Example 6

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

lines = file.readlines()

print(lines)

file.close()

Output

['Sameer\n', 'Ayesha\n', 'Saddam\n']

📌 Explanation
Each line becomes a list element.

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🔹 9. Using with open() (Best Practice)

Python automatically closes file.

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Example 7

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

Output

Sameer
Ayesha
Saddam

📌 Explanation

✔ No need to call close()
✔ Cleaner and safer code

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🔹 10. Creating a New File

Example 8

file = open("students.txt", "x")

file.write("Chandini")

file.close()

📌 Explanation

• "x" creates a new file
• Error occurs if file already exists

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🔹 11. Real-Life Example

Student Record System

name = input("Enter student name: ")

with open("students.txt", "a") as file:
    file.write(name + "\n")

print("Student saved successfully")

Sample Output

Enter student name: Gousya
Student saved successfully

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🔹 12. Common File Methods

Method	Purpose
read()	Reads entire file
readline()	Reads one line
readlines()	Reads all lines
write()	Writes data
close()	Closes file

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🔹 13. Common Mistakes

❌ Forgetting to close file
❌ Using "w" accidentally (deletes content)
❌ File not found error

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