File Input & Output

# The 'with' statement — automatically closes the file
# (even if an exception is raised)
with open("data.txt", "r", encoding="utf-8") as f:
    content = f.read()     # entire file as a string

# Read line by line (memory efficient for large files)
with open("large_file.txt", "r") as f:
    for line in f:
        line = line.strip()  # remove trailing newline
        process(line)

# Read all lines into a list
with open("courses.txt", "r") as f:
    lines = f.readlines()   # ["HTML
", "CSS
", "Python
"]
    lines = [l.strip() for l in lines]  # clean up newlines

# Writing (overwrites if file exists)
with open("output.txt", "w", encoding="utf-8") as f:
    f.write("Line 1
")
    f.write("Line 2
")

# Appending (adds to existing file)
with open("log.txt", "a") as f:
    f.write(f"[2025-01-15] Server started
")

# Writing multiple lines
lines = ["apple", "banana", "mango"]
with open("fruits.txt", "w") as f:
    f.writelines(line + "
" for line in lines)

# JSON — the most common format for data exchange
import json

# Write Python dict/list to JSON file
data = { "courses": 12, "students": 1500, "active": True }
with open("stats.json", "w") as f:
    json.dump(data, f, indent=2)

# Read JSON file into Python dict
with open("stats.json", "r") as f:
    data = json.load(f)

# Convert without file
json_string = json.dumps(data, indent=2)  # dict → string
data        = json.loads(json_string)     # string → dict