Introduction to python - 1

Introduction to Python Programming

• The course focuses on programming with data for the Spring term of 2025. It aims to equip students with essential Python programming skills.

Expressions in Python

Definition and Syntax

• An expression in Python combines values, variables, and operators that can be evaluated to produce a result of a certain type.

• Syntax for expressions: <value/variable> <operator> <value/variable>.

• Example of assigning an evaluated expression to a variable: result = <value/variable> <operator> <value/variable>.

Assignments, Names, and Namespaces

Assignment Statements

• Assignment statements are utilized to assign objects to names. Examples of assignments:

  • x = 10

  • x = "10"

  • y = 30

  • x = "This is a test"

  • z = 20

  • x = y + z

• It's crucial in Python that variable types are not statically assigned; they can change as values are reassigned.

Importance of Naming Variables

• Variable names should:

  • Be unambiguous.

  • Clearly indicate the purpose of the variable.

  • Be understandable to others reading the code.

  • Conform to snake_case convention in Python.

  • Avoid reserved words (keywords) in Python.

Examples of Bad Variable Names

• pikachu = "Carlota"

• potato = 2025

• x = "20/05/2028"

• PI = 3.546

• True = False

• global = "The world"

• Person name = "Laura"

• PersonName = "Lucia"

Examples of Good Variable Names

• user = "Carlota"

• year = 2025

• graduation_date = "20/05/2028"

• new_pi_number = 3.546

• new_true = False

• global_variable = "The world"

• person_name = "Laura"

Namespaces in Python

Definition and Types of Namespaces

• A namespace is a collection of defined symbolic names along with the object information each name references.

• It functions like a dictionary, with keys as object names and values as the objects.

• Four types of namespaces in Python:

  • Built-In

  • Global

  • Enclosing

  • Local

Variable Scope and LEGB Rule

• Python resolves variable references using a defined order:

  1. Local: Looks in the local function's scope.

  2. Enclosing: Checks the enclosing function's scope if it doesn’t find it locally.

  3. Global: Searches in the global scope.

  4. Built-in: Finally looks in the built-in namespace.

Examples of Variable Scope

• Local scope example:

  def example():  
      variable_name = "LEGB rule"  
      print(variable_name)  
  example()  
  print(variable_name)  

• Enclosing scope example:

  def example():  
      first_variable = "outer function"  
      def example_inner():  
          second_variable = "inner function"  
          print(f"{first_variable} // {second_variable}")  
          print(first_variable)  
      example_inner()  
      example()  

• Global scope example:

  variable_name="global function"  
  def example():  
      def example_inner():  
          print(variable_name + " inner")  
      print(variable_name + " outer")  
      example_inner()  

• Built-in scope example:

  from math import pi  
  def example():  
      def example_inner():  
          print(pi)  
      example_inner()  
      print(pi)  

Conditional Statements in Python

Structure of Conditional Statements

• Conditional statements in Python can be structured using three main forms:

  • if [condition]

  • elif [condition]

  • else

• The if and elif statements are utilized when conditions are required, while else is used for all other cases that do not meet previous conditions.

Exercise Examples for User Interaction

• Program prompts for user’s name and responses based on given conditions, illustrating how to construct basic programs using conditional logic:

  1. Responds differently based on user input (e.g. if the name is not Jerry).

  2. Asks for integers and gives feedback based on their value.

Iterations in Python

Types of Loops

• Iterations can be performed using:

  • While loop: Executes as long as a stated condition is true.

  • For loop: Iterates over a data structure (like a list, tuple, dictionary, etc.).

Key Statements for Loops

• Break: Stops the loop's execution.

• Continue: Skips to the next iteration of the loop.

• Range: Generates a sequence of numbers.

Exercises Examples

• Iteration examples that involve user inputs, such as repeatedly asking for numbers while managing conditions and responses, including calculations like factorial.