Python Introduction

What is Python?

Python is a high-level programming language created by Guido van Rossum in 1991. With its easy-to-read syntax and powerful features, it's loved by both beginners and experts.

Key Features

✅ Concise and readable syntax
✅ Extensive standard library
✅ Versatile applications (Web, Data, AI, Automation)
✅ Active community
✅ Cross-platform support

Why Python?

1. Easy to Learn

# Python - Intuitive!
print("Hello, World!")

numbers = [1, 2, 3, 4, 5]
squared = [n ** 2 for n in numbers]
print(squared)  # [1, 4, 9, 16, 25]

2. Versatile

# Web development
from fastapi import FastAPI
app = FastAPI()

# Data analysis
import pandas as pd
df = pd.read_csv('data.csv')

# Machine learning
from sklearn import tree
model = tree.DecisionTreeClassifier()

# Automation
import os
for file in os.listdir('.'):
    print(file)

3. Rich Ecosystem

Web: Django, Flask, FastAPI
Data: NumPy, Pandas, Matplotlib
AI/ML: TensorFlow, PyTorch, scikit-learn
Automation: Selenium, BeautifulSoup, Requests

Installation

Windows

1. Download from Python official website

https://www.python.org/downloads/

2. Check during installation

☑ Add Python to PATH (important!)
☑ Install pip

3. Verify installation

python --version
# Python 3.11.x

pip --version
# pip 23.x.x

macOS

Method 1: Homebrew (recommended)

# Install Homebrew (if not installed)
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

# Install Python
brew install python

# Verify
python3 --version

Method 2: Official download

https://www.python.org/downloads/

Linux (Ubuntu/Debian)

# Update
sudo apt update

# Install Python
sudo apt install python3 python3-pip

# Verify
python3 --version
pip3 --version

Your First Python Program

Starting with REPL

# Launch Python interactive mode
python
# or
python3

>>> print("Hello, Python!")
Hello, Python!

>>> 2 + 3
5

>>> name = "홍길동"
>>> f"안녕하세요, {name}님!"
'안녕하세요, 홍길동님!'

>>> exit()  # Exit

Running from File

Create hello.py

# hello.py
print("Hello, Python!")

name = input("이름을 입력하세요: ")
print(f"안녕하세요, {name}님!")

Execute

python hello.py
# or
python3 hello.py

Setting Up Development Environment

1. Text Editor/IDE

VS Code (recommended)

1. Install VS Code
2. Install Python extension
3. Create file (.py)
4. Run with F5

PyCharm

- Free: Community Edition
- Paid: Professional Edition
- Powerful features, easy for beginners

Jupyter Notebook

# Install
pip install jupyter

# Run
jupyter notebook

# Code interactively in browser

2. Virtual Environment (important!)

Why is it needed?

Use different package versions for each project
Separate from system Python

Create and activate

# Create virtual environment
python -m venv myenv

# Activate
# Windows
myenv\Scripts\activate

# macOS/Linux
source myenv/bin/activate

# Deactivate
deactivate

3. Package Management (pip)

# Install package
pip install requests

# Install multiple
pip install numpy pandas matplotlib

# Install specific version
pip install django==4.2.0

# List installed packages
pip list

# Uninstall package
pip uninstall requests

# Create requirements.txt
pip freeze > requirements.txt

# Install from requirements.txt
pip install -r requirements.txt

Practical Examples

Calculator

def calculator():
    print("=== 간단한 계산기 ===")

    num1 = float(input("첫 번째 숫자: "))
    operator = input("연산자 (+, -, *, /): ")
    num2 = float(input("두 번째 숫자: "))

    if operator == '+':
        result = num1 + num2
    elif operator == '-':
        result = num1 - num2
    elif operator == '*':
        result = num1 * num2
    elif operator == '/':
        result = num1 / num2
    else:
        print("잘못된 연산자입니다.")
        return

    print(f"결과: {result}")

calculator()

Number Guessing Game

import random

def guessing_game():
    answer = random.randint(1, 100)
    attempts = 0

    print("1부터 100 사이의 숫자를 맞춰보세요!")

    while True:
        guess = int(input("숫자 입력: "))
        attempts += 1

        if guess < answer:
            print("더 큰 숫자입니다!")
        elif guess > answer:
            print("더 작은 숫자입니다!")
        else:
            print(f"정답! {attempts}번 만에 맞췄습니다!")
            break

guessing_game()

Python Style Guide

PEP 8 (Python Coding Rules)

# ✅ Good example
def calculate_total(price, quantity):
    total = price * quantity
    return total

user_name = "홍길동"
MAX_SIZE = 100

# ❌ Bad example
def CalculateTotal(Price,Quantity):
    Total=Price*Quantity
    return Total

UserName="홍길동"
maxsize=100

Key Rules

- Indentation: 4 spaces
- Variable names: snake_case
- Class names: PascalCase
- Constants: UPPER_CASE
- Line length: maximum 79 characters

Useful Tips

1. Getting Help

# Function help
help(print)

# Module help
import math
help(math)

# Check object attributes
dir("hello")

2. Interactive Debugging

# Pause code execution
import pdb
pdb.set_trace()

# Or Python 3.7+
breakpoint()

3. Timing Measurement

import time

start = time.time()

# Code to measure
sum([i for i in range(1000000)])

end = time.time()
print(f"실행 시간: {end - start}초")

Frequently Asked Questions

Q1. Python 2 vs Python 3?

A: Use Python 3!

# Python 2 support ended in 2020
# Python 3 is the standard

Q2. python vs python3 command?

A: It depends on the system

# Windows: usually python
python --version

# macOS/Linux: usually python3
python3 --version

# Check and use the right one!

Q3. Which IDE is good?

A: Choose based on preference and purpose

Beginners: VS Code (lightweight and free)
Professional development: PyCharm (powerful features)
Data analysis: Jupyter Notebook (interactive)
Simple tasks: Text editor + Terminal

Q4. Package installation doesn't work!

A: It might be a permission issue

# Add --user option
pip install --user 패키지명

# Or use virtual environment (recommended)
python -m venv myenv
source myenv/bin/activate  # Windows: myenv\Scripts\activate
pip install 패키지명

Next Steps

You're now ready to learn Python basics!

Key Summary:
✅ Python installation and environment setup
✅ REPL and file execution
✅ IDE and virtual environment
✅ Package management with pip
✅ Writing your first program

Next Step: Learn the basics of Python programming in Variables and Types!