Day 6: File Operations - One Week Python

📚 What You'll Learn Today

File operations let your programs read and write data to disk:

Opening and closing files
Reading file contents
Writing to files
The "with" statement (best practice)
Working with CSV files

📂 Opening Files

Use the open() function to work with files:

Basic Syntax:

file = open("filename.txt", "r")  # "r" = read mode
# Do something with file
file.close()
            

File Modes:

Mode	Description
`"r"`	Read (default)
`"w"`	Write (overwrites)
`"a"`	Append (add to end)
`"r+"`	Read and write

📖 Reading Files

Read Entire File:

file = open("myfile.txt", "r")
content = file.read()
print(content)
file.close()
            

Read Line by Line:

file = open("myfile.txt", "r")

for line in file:
    print(line.strip())  # strip() removes newlines

file.close()

Read into List:

file = open("myfile.txt", "r")
lines = file.readlines()
print(lines)  # List of lines
file.close()
            

✍️ Writing Files

Write (overwrites):

file = open("output.txt", "w")
file.write("Hello, World!\n")
file.write("This is line 2.\n")
file.close()
            

Append (add to end):

file = open("output.txt", "a")
file.write("This is added later.\n")
file.close()
            

✅ The "with" Statement

Always use with - it automatically closes the file even if errors occur:

# BEST PRACTICE - Always use this!
with open("myfile.txt", "r") as file:
    content = file.read()
    print(content)
# File automatically closed here!
            

💡 Why use "with"? If your code has an error before calling close(), the file might not be saved properly. The "with" statement guarantees the file is closed.

📊 Working with CSV

CSV (Comma-Separated Values) is great for data:

Reading CSV:

import csv

with open("data.csv", "r") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)
            

Writing CSV:

import csv

data = [
    ["Name", "Age", "City"],
    ["Alex", "25", "NYC"],
    ["Jordan", "30", "LA"]
]

with open("output.csv", "w", newline="") as file:
    writer = csv.writer(file)
    writer.writerows(data)
            

🏋️ Exercise: Todo List App

Create a simple todo list that saves to a file!

# 1. Read existing todos from file
# 2. Add a new todo
# 3. Save back to file
# 4. Display all todos
            

Example Solution:

FILE_NAME = "todos.txt"

def read_todos():
    try:
        with open(FILE_NAME, "r") as f:
            return [line.strip() for line in f]
    except FileNotFoundError:
        return []

def add_todo(todo):
    with open(FILE_NAME, "a") as f:
        f.write(todo + "\n")

# Test it
add_todo("Learn Python")
add_todo("Build a project")
print(read_todos())
            

✅ Key Takeaways

open("file.txt", "r") - read mode
open("file.txt", "w") - write mode (overwrites)
open("file.txt", "a") - append mode
file.read() - read entire file
file.write() - write to file
Always use "with" for safe file handling
import csv for CSV files

🎉 Ready for the Final Day?

Tomorrow is Day 7 - you'll build a complete calculator project!

Marking complete will unlock Day 7!

📁 Day 6: File Operations

📚 What You'll Learn Today

📂 Opening Files

Basic Syntax:

File Modes:

📖 Reading Files

Read Entire File:

Read Line by Line:

Read into List:

✍️ Writing Files

Write (overwrites):

Append (add to end):

✅ The "with" Statement

📊 Working with CSV

Reading CSV:

Writing CSV:

🏋️ Exercise: Todo List App

Example Solution:

✅ Key Takeaways

🎉 Ready for the Final Day?