Day 1: Getting Started

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Variables store data values. Python has several built-in data types:

name = "server01"

count = 5

active = True

cpu_load = 0.75

value = 42
print(type(value))  # <class 'int'>

The print() function displays output on the screen.

print("Hello, admin!")
# Output: Hello, admin!

print("Disk space:", 20, "GB free")
# Output: Disk space: 20 GB free

print("admin", "user1", "user2", sep=", ")
# Output: admin, user1, user2

print("Checking...", end="")
print("Done!")
# Output: Checking...Done!

Convert between data types:

# String to int
port = "8080"
port = int(port)

# Int to string
num = 42
num_str = str(num)

# Float to int (truncates)
value = 3.99
value_int = int(value)  # 3

# Int to bool
num = 1
print(bool(num))  # True

num = 0
print(bool(num))  # False

print(2 + 3)   # 5
print(10 - 4)  # 6
print(3 * 7)   # 21
print(8 / 2)   # 4.0
print(9 % 2)   # 1 (remainder)

print(5 > 2)    # True
print(5 == 5)   # True
print(5 != 3)   # True

print(True and False)  # False
print(True or False)   # True
print(not True)        # False

Lists store multiple values in an ordered sequence:

# Create
users = ["admin", "user1", "user2"]

# Read
print(users[0])  # admin

# Update
users[1] = "guest"

# Delete
del users[2]

# Add item
users.append("user3")

# Check membership
if "admin" in users:
    print("Admin exists!")

# Loop with index
for idx, user in enumerate(users):
    print(f"User {idx}: {user}")

Dictionaries store key-value pairs:

# Create
config = {"host": "localhost", "port": 22}

# Read
print(config["host"])  # localhost

# Safe access
print(config.get("user", "not set"))

# Update
config["port"] = 2222

# Delete
del config["host"]

# Loop
for key, value in config.items():
    print(f"{key}: {value}")

Make decisions in your code:

# Simple if
if 5 > 2:
    print("5 is greater than 2")

# if-else
user = "admin"
if user == "admin":
    print("Welcome, admin!")
else:
    print("Access denied")

# if-elif-else
score = 75
if score > 90:
    print("Excellent")
elif score > 60:
    print("Good")
else:
    print("Needs improvement")

# Membership test
users = ["admin", "user1"]
if "admin" in users:
    print("Admin found!")

Repeat actions multiple times:

# For loop
for i in range(3):
    print(i)  # 0, 1, 2

# Loop through list
for user in users:
    print(user)

# While loop
n = 0
while n < 3:
    print(n)
    n += 1

# Loop with break
for i in range(5):
    if i == 3:
        break
    print(i)  # 0, 1, 2

# Loop with continue
for i in range(5):
    if i % 2 == 0:
        continue
    print(i)  # 1, 3

Reusable blocks of code:

# Simple function
def greet():
    print("Hello!")
greet()

# With argument
def greet_user(name):
    print(f"Hello, {name}!")
greet_user("admin")

# With return value
def add(a, b):
    return a + b
print(add(2, 3))  # 5

# With default argument
def show_port(port=22):
    print(f"Port: {port}")
show_port()    # Port: 22
show_port(80)  # Port: 80

# With docstring
def check_user(username, users):
    """Return True if user exists."""
    return username in users

Modules extend Python's capabilities:

import os
print(os.getcwd())

import math
print(math.sqrt(16))  # 4.0

import random
print(random.randint(1, 10))

from os import getcwd
print(getcwd())

import sys
print(sys.version)

import os
for f in os.listdir('.'):
    print(f)

import shutil
total, used, free = shutil.disk_usage("/")
print(f"Free space: {free // (1024**3)} GB")

def list_files(path="."):
    """List all files in a directory."""
    return os.listdir(path)

print(list_files())