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Data input and output (I/O) are fundamental operations in programming that allow programs to interact with the user and external information sources. Python provides a powerful and intuitive set of tools for working with data, which we will explore in detail in this guide.
Data output in Python: print() function
The print() function is the main tool for displaying information in Python. It provides many features for formatted data output to the console or to files.
Basics of working with print()
The simplest use of the print() function is to output text or variable values:
print("Hello, world!") # Outputs a text string
x = 10
print("The value of x is:", x) # Outputs the text and the value of the variable
Formatting output in Python
Python offers several ways to format strings for beautiful data output:
name = "Anna"
age = 25
salary = 50000.50
# Method .format()
print("Name: {}, Age: {}, Salary: {:.2f}".format(name, age, salary))
# F-strings (recommended method)
print(f"Name: {name}, Age: {age}, Salary: {salary:.2f}")
# The old way of formatting
print("Name: %s, Age: %d, Salary: %.2f" % (name, age, salary))
Parameters of the print() function
The print() function has several useful parameters:
The sep parameter defines the separator between the elements.:
print("apple", "banana", "orange", sep=", ") # Outputs: apple, banana, orange
print("2024", "01", "15", sep="-") # Outputs: 2024-01-15
The end parameter defines the line ending character.:
print("Download", end="")
for i in range(3):
print(".", end="")
print("Done!") # Outputs: Loading... It's done!
The file parameter allows you to send the output to a file.:
with open("log.txt", "w", encoding="utf-8") as file:
print("Information saved to a file", file=file)
Data entry in Python: input() function
The input() function allows you to receive data from the user interactively. It always returns a string that needs to be converted to other data types, if necessary.
Basics of working with input()
# Simple input without invitation
name = input()
print(f"Hello, {name}!")
# Prompt input
age = input("Enter your age: ")
print(f"You are {age} years old")
Data type conversion
Since input() always returns a string, it is necessary to convert the data to the desired type.:
# Convert to integer
age = int(input("Enter your age:"))
# Conversion to a floating point number
height = float(input("Enter your height in meters: "))
# Processing a list of values
numbers = input("Enter numbers separated by a space:").split()
numbers = [int(num) for num in numbers]
Input error handling
It is important to provide for the processing of incorrect input:
while True:
try:
age = int(input("Enter your age: "))
if age < 0:
print("Age cannot be negative")
continue
break
except ValueError:
print("Please enter the correct number")
print(f"Your age: {age}")
Validation of user input
def get_valid_email():
while True:
email = input("Enter email: ")
if "@" in email and "." in email:
return email
print("Incorrect email format")
email = get_valid_email()
print(f"Your email: {email}")
Working with files in Python
Python provides powerful tools for working with files, allowing you to read and write data in various formats.
Writing data to a file
# Writing text to a file
with open("output.txt", "w", encoding="utf-8") as file:
file.write("Hello, world!\n")
file.write("This is the second line\n")
# Writing a list of lines
lines = ["First line", "Second line", "Third line"]
with open("lines.txt", "w", encoding="utf-8") as file:
file.writelines(line + "\n" for line in lines)
Reading data from a file
# Reading the entire file
with open("input.txt", "r", encoding="utf-8") as file:
content = file.read()
print(content)
# Reading the file line by line
with open("input.txt", "r", encoding="utf-8") as file:
for line in file:
print(line.strip()) # strip() deletes newline characters
# Reading a file into a list
with open("input.txt", "r", encoding="utf-8") as file:
lines = file.readlines()
print(lines)
File opening modes
mode| Description | |
|---|---|
"r" |
Read (default) |
"w" |
Recording (overwrites the file) |
"a" |
Adding to the end of the file |
"r+" |
Reading and writing |
"b" |
Binary mode (added to the main mode) |
Working with CSV files
import csv
# Writing a CSV file
data = [
["Name", "Age", "City"],
[Alexey, 30, Moscow],
["Maria", 25, "Saint Petersburg"]
]
with open("data.csv", "w", newline="", encoding="utf-8") as file:
writer = csv.writer(file)
writer.writerows(data)
# Reading a CSV file
with open("data.csv", "r", encoding="utf-8") as file:
reader = csv.reader(file)
for row in reader:
print(row)
Advanced I/O techniques
Formatting numbers and dates
from datetime import datetime
# Formatting numbers
price = 1234.5678
print(f"Price: {price:.2f} rub.") # Price: 1234.57 rub.
print(f"Price: {price:,.2f} rub.") # Price: 1,234.57 rub.
# Formatting dates
now = datetime.now()
print(f"Current date: {now:%d.%m.%Y}")
print(f"Current time: {now:%H:%M:%S}")
Working with JSON files
import json
# Saving data in JSON
data = {
"name": "Ivan",
"age": 30,
"city": "Moscow",
"hobbies": ["programming", "reading", "sports"]
}
with open("data.json", "w", encoding="utf-8") as file:
json.dump(data, file, ensure_ascii=False, indent=2)
# Reading data from JSON
with open("data.json", "r", encoding="utf-8") as file:
loaded_data = json.load(file)
print(loaded_data)
Creating interactive programs
def calculator():
print("A simple calculator")
print("Available operations: +, -, *, /")
while True:
try:
num1 = float(input("Enter the first number: "))
operator = input("Enter the operation (+, -, *, /): ")
num2 = float(input("Enter the second number: "))
if operator == "+":
result = num1 + num2
elif operator == "-":
result = num1 - num2
elif operator == "*":
result = num1 * num2
elif operator == "/":
if num2 == 0:
print("Division by zero is impossible!")
continue
result = num1 / num2
else:
print("Unknown operation")
continue
print(f"Result: {result}")
if input("Continue? (y/n): ").lower() != 'y':
break
except ValueError:
print("Error: enter the correct number")
calculator()
Best practices for working with I/O in Python
1. Always use the context manager with
# Correct
with open("file.txt", "r") as file:
content = file.read()
# Wrong
file = open("file.txt ", "r")
content = file.read()
file.close() # You can forget to close the file
2. Specify the encoding when working with files
with open("file.txt", "r", encoding="utf-8") as file:
content = file.read()
3. Handle exceptions
try:
with open("file.txt", "r") as file:
content = file.read()
except FileNotFoundError:
print("File not found")
except PermissionError:
print("No permission to read the file")
4. Validate user input
def get_positive_number(prompt):
while True:
try:
num = float(input(prompt))
if num > 0:
return num
print("The number must be positive")
except ValueError:
print("Enter the correct number")
Conclusion
Python data input and output provide programmers with powerful tools for creating interactive applications and processing information. Understanding the functions print() and input(), as well as working with files, is the basis for creating functional programs.
Basic principles of working with I/O in Python:
- Use f-strings to format the output
- Always handle exceptions when working with files
- Validate user input
- Use context managers to work with files
- Specify the encoding when working with text files
This knowledge will help you create reliable and user-friendly programs that interact effectively with users and process data in various formats.