Python - Scope (Day 12)

This is a 100 Days challenge to learn a new language (Python). 100 Days of Code - The Complete Python Pro Bootcamp 

I will post some notes to motivate myself to finish this challenge.

Scope

Like an apple tree inside your house fence. Then only you and your family can access this apple tree. If there is an apple tree outside your fence and others. Then everyone can access it.

Local Scope

Ex:

# Custom Function

def log_count():

# Define a Local Scope Variable

    count = 1

    print(count)

# Call a custom function

log_count()

# Try to access a variable which is defined in a custom function

print(count)

Result:

NameError: name 'count' is not defined

The instruction print(count) which is outside of log_count() function will throw an error NameError: name 'count' is not defined because 'count' is in a local scope (Like people who is outside your fence and try to access your apply tree)

Global Scope

Ex:

# Define a Global Scope Variable

count = 1

  # Custom Function

def log_count():

    # Access a global variable

    print(count)

log_count()

# Access a global variable

print(count)

Result:

1

1

Since 'count' is in global scope, everyone can access it no matter he is inside or outside the log_count() function.

Namespace

The concept of Global and Local scope do not only apply to variables, but also basically it apply to everything your named. Everything you named have its namespace, and namespace will be valid in certain scope.

We can modify previous example as below.

Ex:

# Global Scope Variables

count = 1

# Custom Function

def demo():

# Define a Local Function

    def log_count():

# Access a global variable

        print(count)

# Try to access a local function

log_count()

print(count)

Result:

NameError: name 'log_count' is not defined

Then log_count() function will throw an error NameError: name 'log_count' is not defined since log_count is the local function inside demo() function.

Block Scope in Python?

Ex:

score = 70

if score >= 60:

# Define a Local Variable ???

    message = "You Pass"

# Try to access a local variable ???

print(message)

Result:

You Pass

Unlike other language, the example above is totally working in python. Block like 'if', 'while', or 'for' does not count as creating local scope.

Modify Global Variables?

Ex:

# Global Scope Variables

score = 70

# Custom Function

def reset_score():

     # Local Scope Variables

    score = 0

    print(score)

# Call a custom function to reset a global variable

reset_score()

print(score)

Result:

0

70

As we discussed before, the score = 0 will create another local variable inside reset_score function. If the output is done by design, then it is fine, but please don't use the same name like global variables. It will reduce the readability.

Modify Global Variables? - Method 1

However if the result is not what you want (we do want to modify the global variable from 70 to 0), you need to give it a global tag to make it work as expected.

Ex:

# Global Scope Variables

score = 70

# Custom Function

def reset_score():

# Tag score as a global variable

    global score

      # Modify global variable

    score = 0

    print(score)

# Call a custom function to reset a global variable

reset_score()

print(score)

Result:

0

0

Modify Global Variables? - Method 2 (Recommended)

Using function input and output to modify the global variables.

Ex:

# Global Scope Variables

score = 70

# Custom Function to get an input and return an output

def reset_score(score):

    score = 0

    print(score)

    return score

# Passing current global variable and override it by its output

score = reset_score(score)

print(score)

Result:

0

0

Constants V.S. Global Variables

Constants have it naming convention in case you modify it accidently.

Ex:

PI = 3.14159

Challenge - Number Guessing Game

Build a simple number guessing game

* Provide two level: easy and hard

* easy level: 10 attempts

* hard level: 5 attempts

* indicate whether it is too high or low

Flow:

Ex:

import random

EASY_LEVEL_LIVES = 10

HARD_LEVEL_LIVES = 5

# Setup game lives based on selected game level

def chooseGameLevel():

    """Return game lives"""

    mode = input("Choose a difficulty. Type 'easy' or 'hard': ")

    if mode == "easy":

        lives = EASY_LEVEL_LIVES

    else:

        lives = HARD_LEVEL_LIVES

    return lives

 # Game

def game():

    print("Welcome to Number Guessing Game!")

    print("The number is between 1 and 100")

    # Randomly generate a number between 1 and 100

    answer = random.randint(1, 100)

    # Setup game lives

    lives = chooseGameLevel()

    while lives > 0:

        print(f"You have { lives } attemps remainding to

guess the number.")

        guess = int(input("Make a guess: "))

        if guess == answer:

            print(f"You got it! The answer was {answer}")

            return

        if guess > answer:

            print("Too High")

            lives -= 1

        else:

          print("Too Low")

            lives -= 1

        if lives == 0:

            print(f"You have run out of guesses, you lose")

            return

        else:

            print("Guess again.")

game()