# Python Fundamentals Refresher

## Functions with Parameters

Functions are blocks of reusable code. Parameters are like placeholders for values that a function needs to do its job.

*   **Defining a function:**
    ```python
    def greet(name: str, greeting: str):
        # Function code uses name and greeting
        print(f"{greeting}, {name}!")
    ```
*   **Calling a function:**
    ```python
    greet("Alice", "Hello")
    # Output: Hello, Alice!
    ```
*   **Formatting Strings (f-strings):**
    A convenient way to embed expressions inside string literals.
    *   `f"{variable}"`: Inserts the value of `variable`.
    *   `f"{float_variable:.2f}"`: Formats a floating-point number to two decimal places.

## Looping with `range()`

`for` loops are used to repeat a block of code multiple times. `range()` generates a sequence of numbers.

*   **Basic loop:**
    ```python
    for i in range(3):  # i will be 0, 1, 2
        print(i)
    # Output:
    # 0
    # 1
    # 2
    ```
*   **Using the loop variable for numbered lists:**
    `range(len(my_list))` iterates through indices of a list.
    ```python
    items = ["Apple", "Banana", "Cherry"]
    for i in range(len(items)):
        # i starts at 0, so add 1 for 1-based numbering
        print(f"{i + 1}. {items[i]}")
    # Output:
    # 1. Apple
    # 2. Banana
    # 3. Cherry
    ```

## Running Scripts

The `if __name__ == "__main__":` block:
Code inside this block only runs when the script is executed directly (e.g., `python your_script.py`), not when it's imported as a module into another script.

```python
def setup():
    print("Setting up...")

def run_program():
    print("Running program logic...")

if __name__ == "__main__":
    print("Script is being run directly.")
    setup()
    run_program()

Turtle Graphics

1. Setting Up the Canvas (Screen)

The turtle module draws on a window called the "screen".

• Get the screen:

  import turtle
  screen = turtle.Screen()
  

• Set screen size:

  screen.setup(width=600, height=400) # Set window dimensions
  

• Set background color:

  screen.bgcolor("lightblue") # Use color names or hex codes
  

• Control screen updates (for faster drawing): Turn off updates before complex drawing, turn on and update when finished.

  screen.tracer(0) # Turn off updates
  # ... drawing code ...
  screen.update()  # Show the drawing
  screen.tracer(1) # Turn updates back on (optional, often done implicitly by done())
  

• Keep the window open:

  turtle.done() # Or screen.mainloop()
  

2. The Turtle (Pen)

The "turtle" is the cursor that draws on the screen. You can have multiple turtles.

• Create a Turtle:

  artist = turtle.Turtle()
  

• Hide the Turtle icon:

  artist.hideturtle()
  

• Set Speed: Speed can be 1-10 (slowest to fastest) or 0 (no animation, instant drawing).

  artist.speed(0) # Fastest
  artist.speed(5) # Medium speed
  

• Set Pen Color / Fill Color:

  artist.color("red")      # Sets both pen and fill color
  artist.pencolor("blue")  # Sets only pen color
  artist.fillcolor("green")# Sets only fill color
  

• Set Pen Size (Thickness):

  artist.pensize(3) # Set pen thickness to 3 pixels
  

• Pen Control:
  • Lift the pen (stop drawing when moving):

    artist.penup()
    

  • Put the pen down (start drawing when moving):

    artist.pendown()
    

3. Movement and Drawing

Commands to move the turtle and draw lines or shapes. The screen's center is (0, 0).

• Go to a Specific Position: Move the turtle to coordinates (x, y). Draws a line if the pen is down.

  artist.goto(100, 50) # Move to x=100, y=50
  

• Move Forward/Backward: Move the turtle in its current direction.

  artist.forward(100) # Move 100 units forward
  artist.backward(50) # Move 50 units backward
  

• Turning: Change the turtle's direction.

  artist.left(90)      # Turn left by 90 degrees
  artist.right(45)     # Turn right by 45 degrees
  artist.setheading(0) # Set direction to 0 degrees (East)
                       # 0: East, 90: North, 180: West, 270: South
  

• Drawing Shapes (Examples):
  • Square:

    # Assuming pen is down and turtle is at a corner facing along an edge
    side = 50
    for _ in range(4):
        artist.forward(side)
        artist.left(90)
    

  • Circle: Draws a circle with the given radius. The turtle's current position is the bottom of the circle if facing East.

    radius = 30
    artist.circle(radius)
    

4. Filled Shapes

Draw shapes that are filled with a solid color.

• Set Fill Color: Use fillcolor() or the color() command (which sets both pen and fill).

  artist.fillcolor("blue")
  

• Start and End Fill: Call begin_fill() before drawing the shape, and end_fill() after the shape is complete.

  artist.fillcolor("yellow")
  artist.begin_fill()
  # ... drawing commands for the shape (e.g., square, circle, polygon) ...
  artist.end_fill()
  

5. Drawing with Functions

Organize your drawing code into functions for reusability.

• Defining a drawing function: A function can take parameters like position (x, y), size, or color to make it flexible. It often takes the turtle object itself as a parameter.

  def draw_dot_at(t, x, y, dot_color, dot_size):
      t.penup()
      t.goto(x, y)
      t.pendown()
      t.dot(dot_size, dot_color) # Draws a filled circle
  

• Calling a drawing function:

  my_turtle = turtle.Turtle()
  draw_dot_at(my_turtle, 100, 100, "purple", 20) # Draw a purple dot
  draw_dot_at(my_turtle, -50, 0, "orange", 10)  # Draw an orange dot
  

6. Drawing Multiple Shapes with Loops

Use loops to draw the same shape multiple times at different locations or with variations.

• Looping through coordinates: Store positions in a list and iterate through the list.

  positions = [(100, 100), (-50, 0), (0, -150)]
  my_turtle = turtle.Turtle()
  my_turtle.speed(0) # Draw fast
  
  for pos_x, pos_y in positions:
      # Call a drawing function for each position
      draw_dot_at(my_turtle, pos_x, pos_y, "green", 15)
  

• Calculating positions in a loop: Use the loop counter to calculate coordinates.

  my_turtle = turtle.Turtle()
  my_turtle.speed(0)
  
  for i in range(5): # Draw 5 circles
      x = -200 + i * 100 # Space circles 100 units apart horizontally
      y = 0
      my_turtle.penup()
      my_turtle.goto(x, y - 20) # Position for circle bottom (radius 20)
      my_turtle.pendown()
      my_turtle.circle(20)
  

7. Adding Text Labels

Use the write() method to display text on the canvas.

• Writing text: The text is written at the turtle's current position.

  artist.penup()
  artist.goto(0, 150) # Move to position for text
  artist.color("black") # Set text color
  artist.write("My Map Title", align="center", font=("Arial", 16, "bold"))
  

• write() parameters:
  • arg: The string to write.
  • move (optional, boolean): If True, the turtle moves to the end of the text. Default is False.
  • align (optional, string): Alignment of the text relative to the turtle's position ("left", "center", or "right"). Default is "left".
  • font (optional, tuple): A tuple (name, size, style). name is a font family string (e.g., "Arial", "Courier", "Times New Roman"). size is an integer font height. style is a string ("normal", "bold", "italic").