Module 09: Input & OutputConnecting your program to the world
Input is how your program receives information from the outside world. In Python, the input() function pauses execution and waits for the user to type something:
# Basic input
name = input('What is your name? ')
print(f'Hello, {name}!')
# IMPORTANT: input() always returns a string
# You must convert to numbers if needed
age_str = input('How old are you? ')
age = int(age_str) # Convert to integer
# Or in one line:
score = float(input('Enter your score: '))
if age >= 18:
print('You are an adult.')
Displaying Output
You've used print() from the start, but it has more power than you've seen:
# Multiple items
print('Name:', 'Ama', 'Age:', 22)
# Custom separator
print('2025', '06', '15', sep='-') # 2025-06-15
# No newline at end
print('Loading', end='')
print('...', end='')
print(' Done!') # Loading... Done!
# f-strings for formatted output
price = 49.5
print(f'Price: GHS {price:.2f}') # GHS 49.50
quantity = 1234567
print(f'Units sold: {quantity:,}') # 1,234,567
File Handling
File handling lets your program read from and write to files on disk — making data persist beyond the life of the program. Python makes this clean and safe with the with statement.
Reading Files
# Read entire file
with open('data.txt', 'r') as file:
content = file.read()
print(content)
# Read line by line (memory-efficient for large files)
with open('data.txt', 'r') as file:
for line in file:
print(line.strip())
# Read all lines into a list
with open('data.txt', 'r') as file:
lines = file.readlines()
Writing Files
# Write to a file (overwrites if exists)
with open('output.txt', 'w') as file:
file.write('Hello, File World!\n')
file.write('Line 2\n')
# Append to a file (adds to end, preserves existing)
with open('log.txt', 'a') as file:
file.write('User logged in at 09:00\n')
# Write multiple lines at once
students = ['Ama', 'Kofi', 'Abena']
with open('students.txt', 'w') as file:
file.writelines([s + '\n' for s in students])
💡 The with StatementAlways use `with open(...)` for file operations. It automatically closes the file when you're done — even if an error occurs. Unclosed files can cause data loss and resource leaks.
Working with External Data
CSV (Comma-Separated Values) files are the most common format for data exchange. Python's csv module makes them easy to work with:
import csv
# Writing CSV
data = [
['Name', 'Score', 'Grade'],
['Ama', 95, 'A'],
['Kofi', 78, 'B'],
['Abena', 88, 'B+']
]
with open('grades.csv', 'w', newline='') as file:
writer = csv.writer(file)
writer.writerows(data)
# Reading CSV
with open('grades.csv', 'r') as file:
reader = csv.DictReader(file)
for row in reader:
print(f"{row['Name']} scored {row['Score']}")