Dictionaries, files, and modules

What are dictionaries

A dictionary in Python is a collection of key-value pairs. Think of it like a creature's stat card: on the left you have the label (name, type, HP) and on the right you have the corresponding value.

You create a dictionary using curly braces {}:

Result:

{'name': 'Flamarion', 'type': 'fire', 'hp': 95, 'attack': 28}

Each element in the dictionary has two parts separated by :, the key (on the left) and the value (on the right). Keys are usually strings, and values can be anything: strings, numbers, lists, even other dictionaries.

You can also create an empty dictionary and add elements as you go:

Result:

{'name': 'Aquadon', 'type': 'water', 'hp': 110, 'attack': 22}

Accessing and modifying values

To get a value from a dictionary, you use the key inside square brackets:

Result:

Creature name: Flamarion
Hit points: 95

If you try to access a key that does not exist, you get a KeyError. To avoid that, you can use the get() method, which returns None (or a default value) if the key is missing:

Result:

Speed: 0

You can modify values the same way you set them initially:

Result:

HP before battle: 95
HP after battle: 65
Attack after evolution: 42

Iterating over dictionaries

When you want to display all the information about a creature, you use a for loop. The items() method gives you access to each key-value pair:

Result:

=== Creature Stat Card ===
name : Terravolt
type : earth
hp : 130
attack : 35

You can also iterate over just the keys or just the values:

Result:

name
type
hp
attack
---
Terravolt
earth
130
35

You can check if a key exists in a dictionary with the in operator:

Result:

The creature has 130 hit points.
We do not know this creature's speed.

The zip() function

Imagine you have two separate lists: one with creature names and one with their types. The zip() function combines them into pairs, like a zipper joining two sides:

Result:

[('Flamarion', 'fire'), ('Aquadon', 'water'), ('Terravolt', 'earth')]

Super useful: you can directly transform the result of zip() into a dictionary with dict():

Result:

{'Flamarion': 'fire', 'Aquadon': 'water', 'Terravolt': 'earth'}

In a single line you created a complete dictionary. That is the power of zip().

The split() method

The split() method takes a string and cuts it into pieces, returning a list. By default, it splits on spaces:

Result:

['Flamarion', 'fire', '95', '28']

You can also specify a different separator. For example, if the data is separated by commas:

Result:

['Aquadon', 'water', '110', '22']
{'name': 'Aquadon', 'type': 'water', 'hp': 110, 'attack': 22}

Notice that we used int() for HP and attack, because split() always returns strings, even if they look like numbers.

The sorted() function

The sorted() function returns a sorted version of a list, without modifying the original list:

Result:

Original: [12, 5, 23, 8, 17, 3]
Sorted: [3, 5, 8, 12, 17, 23]
Descending: [23, 17, 12, 8, 5, 3]

It also works with strings, sorting them in alphabetical order:

Result:

Alphabetical order: ['Aquadon', 'Breezel', 'Flamarion', 'Terravolt']

You can also sort the keys of a dictionary:

Result:

Creatures sorted by name:
  Aquadon: 110 HP
  Flamarion: 95 HP
  Terravolt: 130 HP

Deleting from dictionaries (del and pop)

You have two main ways to delete elements from a dictionary.

del removes a key completely:

Result:

Before: {'name': 'Flamarion', 'type': 'fire', 'hp': 95, 'attack': 28}
After del: {'name': 'Flamarion', 'hp': 95, 'attack': 28}

pop() removes the key and returns the deleted value. Useful if you need it:

Result:

Saved HP: 110
Remaining dictionary: {'name': 'Aquadon', 'type': 'water', 'attack': 22}

With pop() you can also specify a default value, so you do not get an error if the key does not exist:

Result:

Ability: none

Working with files

Now comes the interesting part: saving data to a file. Think of it like a save game. You write data to disk so you can find it again tomorrow.

To write to a file, you use open() with the "w" (write) mode:

A few important things:

• "w" means "write". If the file already exists, the old content is erased
• "a" (append) adds to the end without erasing what was there before
• "\n" creates a new line in the file
• str(value) converts numbers to text, because write() only accepts strings
• Do not forget file.close(), otherwise data might be lost

Reading files

To load data back, you open the file with the "r" (read) mode:

Result:

=== Save Game ===
name: Flamarion
type: fire
hp: 95
attack: 28

If you want to read line by line, use readlines():

This is useful when you want to process each line separately, for example to reconstruct a dictionary from saved data:

Result:

Loaded creature: {'name': 'Flamarion', 'type': 'fire', 'hp': '95', 'attack': '28'}

The with open() syntax

In the examples above, you had to remember to call close() after each open(). If you forget, problems can arise. Data might not be fully saved or the file might remain locked.

Python offers a more elegant solution: with open(). This syntax automatically closes the file when the code block ends, even if an error occurs:

Result:

Saved successfully!
name: Breezel
type: wind
hp: 80
attack: 24

Always use with open() instead of plain open(). It is safer, cleaner, and you do not have to worry about forgetting to close the file.

Modules: random and os

Modules are like extensions that you load into your program. Python comes with dozens of built-in modules, and two of the most useful ones are random and os.

The random module

random lets you generate random values, perfect for game mechanics:

Each run will produce different results, and that is exactly the point. The main functions are:

• random.randint(a, b) - random integer between a and b (inclusive)
• random.choice(list) - picks a random element from a list
• random.shuffle(list) - shuffles the elements of a list (modifies the list directly)

The os module

os gives you access to operating system functions. You can check if a file exists, create folders, or list the contents of a directory:

The os module is especially useful when working with files and you want to make sure everything exists before you try to read or write.

You can also import specific functions with from ... import:

Complete game code: Python Kingdom (Lesson 9 - FINAL)

Congratulations! This is the complete Python Kingdom game with ALL systems: character creation, battle, inventory, shop, dungeon, puzzle room, save/load, and the final boss fight!

Bonus: Simple graphics with turtle

The turtle module in Python lets you draw simple graphics. Here are two examples you can add to your game: an HP bar and a mini-map.

HP bar - a green rectangle that shrinks as the hero loses health:

Mini-map - draws dungeon rooms as colored squares:

Copy the turtle code into a separate .py file and run it to see the graphics. The turtle module opens a window with the drawing.