File Handling in Python (Basics)

Python reads and writes files with the built-in open() function:

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

Always close a file after use, or better, use the with statement: it closes the file for you, even if an error happens.

1. Write to a file ("w" mode)

file = open(file_name, "w")
file.write("Hello Students\n")       # \n means new line
file.write("Welcome to File Handling\n")
file.close()                         # don't forget to close
print("1. Data written to", file_name)

2. Read the whole file ("r" mode)

file = open(file_name, "r")
data = file.read()
print("\n2. Full file content:")
print(data)
file.close()

3. "with" statement (best way)

"with" closes the file automatically, even if an error happens.

with open(file_name, "r") as file:
    print("3. Read using with:")
    print(file.read())

4. Append to a file ("a" mode)

Old content stays, new content is added at the end.

with open(file_name, "a") as file:
    file.write("Python is easy\n")
    file.write("Practice daily\n")
print("4. Two more lines appended")

5. Read one line at a time

with open(file_name, "r") as file:
    first_line = file.readline()     # reads only the first line
    second_line = file.readline()    # reads the next line
    print("\n5. readline():")
    print("First line :", first_line.strip())   # strip() removes \n
    print("Second line:", second_line.strip())

6. Read all lines into a list

with open(file_name, "r") as file:
    lines = file.readlines()
print("\n6. readlines() gives a list:")
print(lines)

7. Loop over the file line by line

print("\n7. Loop over lines with line numbers:")
with open(file_name, "r") as file:
    line_no = 1
    for line in file:
        print(line_no, "->", line.strip())
        line_no += 1

8. Write a list of lines

fruits = ["Apple\n", "Banana\n", "Mango\n"]
with open("fruits.txt", "w") as file:
    file.writelines(fruits)
print("\n8. fruits.txt created using writelines()")

9. Count lines, words and characters

with open(file_name, "r") as file:
    content = file.read()
print("\n9. Counting in", file_name)
print("Lines     :", len(content.splitlines()))
print("Words     :", len(content.split()))
print("Characters:", len(content))

10. Check if a file exists

print("\n10. Check file exists:")
if os.path.exists("fruits.txt"):
    print("fruits.txt exists")
else:
    print("fruits.txt not found")

11. Handle "file not found" error

print("\n11. Reading a missing file:")
try:
    with open("no_such_file.txt", "r") as file:
        print(file.read())
except FileNotFoundError:
    print("Error: file not found")

12. Rename and delete a file

os.rename("fruits.txt", "my_fruits.txt")
print("\n12. fruits.txt renamed to my_fruits.txt")

os.remove("my_fruits.txt")
print("    my_fruits.txt deleted")