python.md

The Absolute Basics

• Variables (Assignments): Assigning values to names. Python is dynamically typed, so no explicit type declaration is needed.

  # Your app's nameapp_name="SomeService"# How many times you've restarted your dev environment todayrestarts_today=7# Is it deployed?is_deployed=True

• Code Blocks (Indentation): Python uses indentation (usually 4 spaces) to define code blocks, instead of braces or keywords.

  # This is a 'function' block.defgreet(name):
  print(f"Hello, {name}!") # This line is part of the 'greet' block.print("Nice to see you.") # So is this one.# This is an 'if' block.ifis_deployed:
  print("Application is running smoothly!")
  else:
  print("Deployment pending...")

• Comments:

  # This function handles all the cat GIFs.# Seriously, all of them.'''Multi-line comment for when you have a lotof wisdom to impart. Or just a long rant.'''"""Another way to write multi-line comments,often used for docstrings."""

---

Data Types

• Strings (str): Immutable sequences of characters.

  greeting="Hello, developer!"# f-strings for dynamic strings (Python 3.6+).user_name="DevOps Dan"full_greeting=f"Hey there, {user_name}! Ready to code?"

• Numbers (int, float, complex):

  port=8080# intversion=1.23# floatcomplex_num=3+2j# complex

• Booleans (bool):True or False. Case-sensitive.

  debug_mode=Trueproduction_ready=False

• Lists (list): Mutable, ordered collections of items. Enclosed in square brackets [].

  favorite_languages= ["Go", "Python", "JavaScript"]
  # Mix and matchmixed_bag= ["one", 2, True]

• Tuples (tuple): Immutable, ordered collections of items. Enclosed in parentheses ().

  coordinates= (10, 20)
  # coordinates[0] = 5 # This would cause an error

• Dictionaries (dict): Mutable, unordered collections of key-value pairs. Enclosed in curly braces {}.

  user_details= {
  "name": "Ops Dan",
  "email": "dan@dev.com",
  "role": "Cloudy McCloudster"
  }

• Sets (set): Mutable, unordered collections of unique elements. Enclosed in curly braces {}.

  unique_ids= {1, 2, 2, 3, 1} # Evaluates to {1, 2, 3}

• None (NoneType): Represents the absence of a value, similar to null in other languages.

  # Use this when a value is optional or not set.optional_setting=None

---

Expressions & Operators

• References (Variables, Attributes, Indices):

  # Grab a variable's valueaws_region="us-east-1"region=aws_region# Accessing list elements by indexfirst_lang=favorite_languages[0] # "Go"# Accessing dictionary values by keyuser_name=user_details["name"] 

• Operators: All your basic math (+, -, *, /, // (floor), % (modulo), ** (exponent)), comparisons (==, !=, <, <=, >, >=), and logic (and, or, not).

  is_admin=user_details["role"] =="admin"oruser_details["name"] =="root"

• Conditional (Ternry Operator):value_if_true if condition else value_if_false

  is_prod=Trueinstance_type="m5.large"ifis_prodelse"t3.micro"

• f-strings (Interpolation - Python 3.6+): A powerful way to embed expressions inside string literals.

  environment="dev"server_id=f"app-{environment}-{1}"# app-dev-1

---

Built-in Functions

• Strings:

  • "HELLO".lower() -> "hello"
  • "world".upper() -> "WORLD"
  • "-".join(["app", "01"]) -> "app-01"
  • "a,b,c".split(",") -> ['a', 'b', 'c']
  • " trim me ".strip() -> "trim me"

• Collections:

  • len(["a", "b", "c"]) -> 3
  • list_data = ["x", "y", "z"]; list_data[1] -> "y"
  • my_dict = {"a": "1", "b": "2"}; my_dict.get("b", "default") -> "2"
  • my_dict.keys() -> dict_keys(['a', 'b'])
  • my_dict.values() -> dict_values(['1', '2'])

• Numeric:

  • abs(-5) -> 5
  • math.ceil(3.14) (requires import math) -> 4
  • math.floor(3.99) (requires import math) -> 3
  • round(3.14159, 2) -> 3.14

• Type Conversions:

  • int("123") -> 123
  • str(123) -> "123"
  • float("3.14") -> 3.14
  • list(my_tuple)
  • tuple(my_list)

---

Input & Output

• User Input:

  user_name=input("Enter your name: ")
  print(f"Hello, {user_name}!")

• Printing to Console:

  print("Hello, World!")
  print("Name:", user_name, "Age:", 30)

• File Handling:

  # Writing to a filewithopen("my_file.txt", "w") asf:
  f.write("Hello from Python!\n")
  f.write("This is a new line.")
  # Reading from a filewithopen("my_file.txt", "r") asf:
  content=f.read()
  print(content)
  # Reading line by linewithopen("my_file.txt", "r") asf:
  forlineinf:
  print(line.strip()) # .strip() removes leading/trailing whitespace includiing newline

---

Control Flow

• Conditional Statements (if/elif/else):

  age=20ifage<18:
  print("Minor")
  elifage<65:
  print("Adult")
  else:
  print("Senior")

• For Loops: Iterating over sequences (lists, tuples, strings, dictionaries, ranges).

  # Iterate over a range of numbersforiinrange(5): # 0, 1, 2, 3, 4print(i)
  # Iterate over a listfruits= ["apple", "banana", "cherry"]
  forfruitinfruits:
  print(fruit)
  # Iterate with indexforindex, fruitinenumerate(fruits):
  print(f"{index}: {fruit}")
  # Iterate over dictionary itemsforkey, valueinuser_details.items():
  print(f"{key}: {value}")

• While Loops: Repeats as long as a condition is true.

  count=0whilecount<3:
  print(count)
  count+=1

• Loop Control (break, continue):

  foriinrange(10):
  ifi==3:
  continue# Skip to the next iteration if i is 3ifi==7:
  break# Exit the loop if i is 7print(i)

---

Functions

• Defining a Function: Reusable blocks of code.

  defgreet(name, greeting="Hello"): # 'greeting' has a default value""" This function greets a person. Args: name (str): The name of the person. greeting (str): The greeting message (default is "Hello"). Returns: str: The full greeting message. """returnf"{greeting}, {name}!"message=greet("Alice")
  print(message) # Hello, Alice!print(greet("Bob", "Hi")) # Hi, Bob!

• Arbitrary Arguments (*args, **kwargs):

  • *args: Collects positionl arguments into a tuple.
  • **kwargs: Collects keyword arguments into a dictionary.

  defsum_all(*numbers):
  returnsum(numbers)
  print(sum_all(1, 2, 3, 4)) # 10defcreate_user(**details):
  print("Creating user with details:")
  forkey, valueindetails.items():
  print(f" {key}: {value}")
  create_user(name="Charlie", age=40, city="London")

• Lambda Functions (Anonymous Functions): Small, single-expression functions.

  add_one=lambdax: x+1print(add_one(5)) # 6

---

Data Structures & Comprehensions

• List Comprehensions: Concise way to create lists.

  squares= [x**2forxinrange(5)] # [0, 1, 4, 9, 16]even_numbers= [xforxinrange(10) ifx%2==0] # [0, 2, 4, 6, 8]

• Dictionary Comprehensions:

  squares_dict= {x: x**2forxinrange(5)} # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

• Set Comprehensions:

  unique_letters= {charforcharin"hello world"ifchar.isalpha()} # {'h', 'e', 'l', 'o', ' ', 'w', 'r', 'd'}

---

Object-Oriented Programming (OOP) Basics

• Classes & Objects: Blueprints for creating objects (instances).

  classDog:
  # Class attributespecies="Canis familiaris"# Constructor (initializer)def__init__(self, name, age):
  self.name=name# Instance attributeself.age=age# Instance attribute# Instance methoddefbark(self):
  returnf"{self.name} says Woof!"# Another instance methoddefdescription(self):
  returnf"{self.name} is {self.age} years old."# Create objects (instances)my_dog=Dog("Buddy", 3)
  your_dog=Dog("Lucy", 5)
  print(my_dog.description()) # Buddy is 3 years old.print(your_dog.bark()) # Lucy says Woof!print(Dog.species) # Canis familiaris

• Inheritance: Creating new classes from existing ones.

  classGoldenRetriever(Dog):
  def__init__(self, name, age, likes_swimming=True):
  super().__init__(name, age) # Call parent class constructorself.likes_swimming=likes_swimmingdefbark(self): # Method overridingreturnf"{self.name} says happy Woof!"golden=GoldenRetriever("Goldie", 2)
  print(golden.description()) # Goldie is 2 years old.print(golden.bark()) # Goldie says happy Woof!print(golden.likes_swimming) # True