File Handling

Reading from and writing to files in Python.

Opening Files

Use open() function to open files.
Modes: 'r' (read), 'w' (write), 'a' (append), 'r+' (read/write)
Always close files with close() or use 'with' statement.

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

# Better: using 'with' (auto-closes)
with open("data.txt", "r") as file:
    content = file.read()
    print(content)
# File automatically closed here

Reading Files

read(): Read entire file
readline(): Read one line
readlines(): Read all lines into list
Iterate over file object for line-by-line reading

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

# Read line by line
with open("data.txt", "r") as file:
    for line in file:
        print(line.strip())  # strip() removes newline

# Read all lines into list
with open("data.txt", "r") as file:
    lines = file.readlines()
    print(lines)

Writing Files

'w' mode: Creates new file or overwrites existing
'a' mode: Appends to existing file
write(): Write string to file
writelines(): Write list of strings

# Write to file (overwrites)
with open("output.txt", "w") as file:
    file.write("Hello, World!\n")
    file.write("Python is awesome!\n")

# Append to file
with open("output.txt", "a") as file:
    file.write("This is appended\n")

# Write multiple lines
lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
with open("output.txt", "w") as file:
    file.writelines(lines)

Working with Paths

Use os.path or pathlib for file paths.
Check if file exists before opening.
Get file information (size, modification time).

import os

# Check if file exists
if os.path.exists("data.txt"):
    print("File exists!")

# Get file size
size = os.path.getsize("data.txt")
print(f"File size: {size} bytes")

# List files in directory
files = os.listdir(".")
print(files)

# Join paths safely
path = os.path.join("folder", "subfolder", "file.txt")

Exception Handling

Use try-except to handle file errors.
Common errors: FileNotFoundError, PermissionError
Always handle potential file operation failures.

# Safe file reading
try:
    with open("data.txt", "r") as file:
        content = file.read()
        print(content)
except FileNotFoundError:
    print("File not found!")
except PermissionError:
    print("Permission denied!")
except Exception as e:
    print(f"An error occurred: {e}")