07 - File Handling

📌 What You'll Learn

• •Opening and closing files
• •Reading files (text and binary)
• •Writing files
• •File modes
• •Working with file paths
• •JSON and CSV files
• •Context managers

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📂 Opening and Closing Files

Basic File Operations

# Open a file
file = open('myfile.txt', 'r')  # 'r' = read mode

# Do something with the file
content = file.read()

# Always close the file!
file.close()

Context Manager (Recommended!)

# Automatically closes the file
with open('myfile.txt', 'r') as file:
    content = file.read()
# File is automatically closed here

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📖 File Modes

# Examples
open('file.txt', 'r')      # Read text
open('file.txt', 'w')      # Write text
open('file.txt', 'rb')     # Read binary
open('file.txt', 'wb')     # Write binary
open('file.txt', 'r+')     # Read and write

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📖 Reading Files

Read Entire File

with open('file.txt', 'r') as f:
    content = f.read()
    print(content)

Read Line by Line

# Read all lines into a list
with open('file.txt', 'r') as f:
    lines = f.readlines()  # List of lines with \n

# Read lines without \n
with open('file.txt', 'r') as f:
    lines = f.read().splitlines()

# Iterate line by line (memory efficient)
with open('file.txt', 'r') as f:
    for line in f:
        print(line.strip())  # Remove trailing whitespace

Read Specific Amount

with open('file.txt', 'r') as f:
    # Read first 100 characters
    chunk = f.read(100)

    # Read one line
    line = f.readline()

    # Read first 5 lines
    for i in range(5):
        line = f.readline()
        print(line)

File Position

with open('file.txt', 'r') as f:
    # Get current position
    pos = f.tell()

    # Move to position
    f.seek(0)      # Beginning
    f.seek(10)     # 10th byte
    f.seek(0, 2)   # End of file

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✏️ Writing Files

Write Text

# Write (overwrites existing content)
with open('file.txt', 'w') as f:
    f.write('Hello, World!\n')
    f.write('Second line\n')

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

Append to File

with open('file.txt', 'a') as f:
    f.write('This is appended\n')

Print to File

with open('file.txt', 'w') as f:
    print('Hello', file=f)
    print('World', file=f)

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📁 Working with Paths

Using os.path

import os

# Current directory
current = os.getcwd()

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

# Check existence
exists = os.path.exists(path)
is_file = os.path.isfile(path)
is_dir = os.path.isdir(path)

# Get parts
dirname = os.path.dirname('/path/to/file.txt')   # /path/to
basename = os.path.basename('/path/to/file.txt') # file.txt
name, ext = os.path.splitext('file.txt')         # ('file', '.txt')

# Absolute path
abs_path = os.path.abspath('file.txt')

Using pathlib (Modern Approach)

from pathlib import Path

# Create path
p = Path('folder') / 'subfolder' / 'file.txt'

# Properties
print(p.exists())
print(p.is_file())
print(p.parent)      # folder/subfolder
print(p.name)        # file.txt
print(p.stem)        # file
print(p.suffix)      # .txt

# Read/write with pathlib
path = Path('file.txt')
path.write_text('Hello, World!')
content = path.read_text()

# Binary
path.write_bytes(b'binary data')
data = path.read_bytes()

# List files
for file in Path('.').glob('*.txt'):
    print(file)

# Recursive search
for file in Path('.').rglob('*.py'):
    print(file)

---

📊 Working with JSON

import json

# Python to JSON
data = {
    'name': 'Alice',
    'age': 25,
    'hobbies': ['reading', 'coding']
}

# Write to file
with open('data.json', 'w') as f:
    json.dump(data, f, indent=2)

# Read from file
with open('data.json', 'r') as f:
    loaded = json.load(f)

# String conversion
json_str = json.dumps(data, indent=2)
parsed = json.loads(json_str)

---

📋 Working with CSV

import csv

# Write CSV
data = [
    ['Name', 'Age', 'City'],
    ['Alice', 25, 'New York'],
    ['Bob', 30, 'Los Angeles'],
    ['Charlie', 35, 'Chicago']
]

with open('data.csv', 'w', newline='') as f:
    writer = csv.writer(f)
    writer.writerows(data)

# Read CSV
with open('data.csv', 'r') as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

# Dictionary CSV
with open('data.csv', 'w', newline='') as f:
    fieldnames = ['name', 'age', 'city']
    writer = csv.DictWriter(f, fieldnames=fieldnames)
    writer.writeheader()
    writer.writerow({'name': 'Alice', 'age': 25, 'city': 'NYC'})

with open('data.csv', 'r') as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row['name'], row['age'])

---

🔒 Exception Handling with Files

# Handle file errors
try:
    with open('nonexistent.txt', 'r') as f:
        content = f.read()
except FileNotFoundError:
    print("File not found!")
except PermissionError:
    print("Permission denied!")
except IOError as e:
    print(f"I/O error: {e}")

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🔧 Useful File Operations

Copy, Move, Delete

import shutil
import os

# Copy file
shutil.copy('source.txt', 'destination.txt')

# Copy with metadata
shutil.copy2('source.txt', 'destination.txt')

# Move/rename
shutil.move('old_name.txt', 'new_name.txt')

# Delete file
os.remove('file.txt')

# Delete directory (empty)
os.rmdir('empty_folder')

# Delete directory (with contents)
shutil.rmtree('folder_with_contents')

Create Directories

import os
from pathlib import Path

# os way
os.makedirs('folder/subfolder', exist_ok=True)

# pathlib way
Path('folder/subfolder').mkdir(parents=True, exist_ok=True)

Temporary Files

import tempfile

# Create temporary file
with tempfile.NamedTemporaryFile(mode='w', delete=False) as f:
    f.write('Temporary content')
    temp_path = f.name

# Create temporary directory
with tempfile.TemporaryDirectory() as tmpdir:
    print(f"Created temp dir: {tmpdir}")
    # Directory is deleted when block ends

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📝 Binary Files

# Read binary
with open('image.png', 'rb') as f:
    data = f.read()

# Write binary
with open('copy.png', 'wb') as f:
    f.write(data)

# Reading in chunks
with open('large_file.bin', 'rb') as f:
    while True:
        chunk = f.read(1024)  # Read 1KB at a time
        if not chunk:
            break
        # Process chunk

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🎯 Next Steps

After mastering file handling, proceed to 08_error_handling to learn about exceptions!