File I/O and pathlib¶

# Read entire file
with open('data.txt', 'r', encoding='utf-8') as f:
    content = f.read()

# Read line by line (memory efficient)
with open('data.txt', encoding='utf-8') as f:
    for line in f:
        line = line.strip()  # remove trailing \n
        process(line)

# Read all lines as list
lines = f.readlines()  # ['line1\n', 'line2\n', ...]

with open('output.txt', 'w', encoding='utf-8') as f:
    f.write('Hello\n')           # no auto newline
    f.writelines(['a\n', 'b\n']) # no auto newline between items
    print('Hello', file=f)       # adds \n automatically

import csv

# Reading
with open('data.csv', encoding='utf-8') as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row['name'], row['age'])

# Writing
with open('out.csv', 'w', newline='', encoding='utf-8') as f:
    writer = csv.writer(f)
    writer.writerow(['name', 'age'])
    writer.writerows([['Alice', 30], ['Bob', 25]])

import json

# Reading
with open('data.json', encoding='utf-8') as f:
    data = json.load(f)

# Writing
with open('out.json', 'w', encoding='utf-8') as f:
    json.dump(data, f, indent=4, ensure_ascii=False)

# String operations
data = json.loads('{"name": "Alice"}')
json_str = json.dumps(data, indent=2)

from pathlib import Path

p = Path('dir/subdir/file.txt')
p = Path.home() / 'Documents' / 'file.txt'  # / joins paths
p = Path.cwd()

# Properties
p.name         # 'file.txt'
p.stem         # 'file'
p.suffix       # '.txt'
p.parent       # Path('dir/subdir')
p.exists()     # True/False
p.is_file()    # True/False
p.is_dir()     # True/False

# Read/write shortcuts
text = p.read_text(encoding='utf-8')
p.write_text('content', encoding='utf-8')

# Directory operations
p.mkdir(parents=True, exist_ok=True)
list(Path('.').glob('*.py'))        # all .py files
list(Path('.').rglob('*.py'))       # recursive glob

# Iteration
for item in Path('.').iterdir():
    print(item.name, item.is_file())

import os

os.path.join('dir', 'sub', 'file.txt')
os.path.basename('/a/b/file.txt')    # 'file.txt'
os.path.dirname('/a/b/file.txt')     # '/a/b'
os.path.splitext('file.txt')         # ('file', '.txt')
os.path.exists('file.txt')
os.path.getsize('file.txt')          # bytes

# Walk directory tree
for dirpath, dirnames, filenames in os.walk('.'):
    for f in filenames:
        print(os.path.join(dirpath, f))

import shutil
shutil.copy('src.txt', 'dst.txt')        # copy file
shutil.copy2('src.txt', 'dst.txt')       # copy with metadata
shutil.copytree('src_dir', 'dst_dir')    # copy directory tree
shutil.rmtree('dir')                     # remove directory tree

import tempfile

with tempfile.NamedTemporaryFile(mode='w', suffix='.txt', delete=False) as f:
    f.write('temp data')
    print(f.name)  # path to temp file