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Python Write/Create Files

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In Python, you can create and write to files using the open() function with the modes "w", "a", or "x".

🔹 w – Write (Overwrite)

f = open("demo.txt", "w")
f.write("This is a new line.")
f.close()

✅ If the file doesn't exist, it will be created.
⚠️ If it exists, it will overwrite everything.

🔹 a – Append (Add at End)

f = open("demo.txt", "a")
f.write("\nAnother line added.")
f.close()

✅ Adds content to the end without deleting existing data.

🔹 x – Create (Error if File Exists)

f = open("newfile.txt", "x")
f.write("File created using x mode.")
f.close()

❌ Raises an error if the file already exists.

🔹 Write Multiple Lines

f = open("demo.txt", "w")
f.writelines(["Line 1\n", "Line 2\n", "Line 3\n"])
f.close()

✅ writelines() takes a list of strings.

🔹 Write in Binary

with open("binaryfile.bin", "wb") as f:
    f.write(b"This is binary data.")

🔹 Best Practice: Use with

with open("demo.txt", "w") as f:
    f.write("Safe writing using with.")

✅ File automatically closes after use.

🔹 Check If File Exists Before Writing

import os

if not os.path.exists("demo.txt"):
    f = open("demo.txt", "w")
    f.write("File created safely.")
    f.close()

Practice Questions

Q1. Write a Python program to write "Hello World" to a file using "w" mode.

Q2. Write a Python program to create a file only if it doesn’t exist using "x" mode.

Q3. Write a Python program to append a new line to notes.txt using "a" mode.

Q4. Write a Python program to overwrite the contents of log.txt with a new message using "w" mode.

Q5. Write a Python program to write multiple lines to a file using the writelines() method.

Q6. Write a Python program to write a binary string to a .bin file using "wb" mode.

Q7. Write a Python program to use with open() to write to a file safely and automatically close it.

Q8. Write a Python program to check if a file exists before writing to it using "w" mode, using os.path.exists().

Q9. Write a Python program to create a function that takes user input and saves it to a file.

Q10. Write a Python program to append today’s date to a file, using the datetime module.

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Python

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Introduction to Python

Python Basics

Cotrol Structures

Data Structures

Date and Time

Functions and Module

File Handling

Python OOP

Advanced Concepts

Python DSA

Searching Algorithms

Sorting Algorithms

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