London | 25-SDC-Nov | Zohreh Kazemianpour | Sprint 5 | Prep Exercises

.gitignore

@@ -1 +1,3 @@
 node_modules
+.venv/
+prep

exercises-sprint5/bank.py

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+def open_account(balances: dict, name: str, amount: int) -> None:
+    balances[name] = amount
+
+def sum_balances(accounts: dict) -> int:
+    total = 0
+    for name, pence in accounts.items():
+        print(f"{name} had balance {pence}")
+        total += pence
+    return total
+
+def format_pence_as_string(total_pence: int) -> str:
+    if total_pence < 100:
+        return f"{total_pence}p"
+    pounds = int(total_pence / 100)
+    pence = total_pence % 100
+    return f"£{pounds}.{pence:02d}"
+
+balances = {
+    "Sima": 700,
+    "Linn": 545,
+    "Georg": 831,
+}
+
+open_account(balances, "Tobi", 913)
+open_account(balances, "Olya", 713)
+
+total_pence = sum_balances(balances)
+total_string = format_pence_as_string(total_pence)
+
+print(f"The bank accounts total {total_string}")
+
+
+
+
+# When I ran mypy I got these errors:
+
+# Error 1: bank.py:24: error: Missing positional argument "amount" in call to "open_account" [call-arg]
+# The function open_account expects three arguments but only two have been passed. We need to add one more argument.
+
+# Error 2: Argument 1 has incompatible type "str"; expected "dict"
+# By adding balances as the first argument, this will be solved as well.
+
+# Error 3: Argument 2 has incompatible type "float"; expected "str"
+# 9.13 is in the wrong position, and it's a float not an int.
+
+# Error 4: Missing positional argument "amount" in call to "open_account"
+# Same problem as Error 1 missing balances and wrong types.
+
+# Error 5: bank.py:25: error: Argument 1 to "open_account" has incompatible type "str"; expected "dict[Any, Any]"
+# Line 25 has two bugs: balances should be passed as the first argument, and the third argument is passed as a string which should be an int.
+
+# Error 6: bank.py:28: error: Name "format_pence_as_str" is not defined [name-defined]
+# Typo! Should be format_pence_as_string.

exercises-sprint5/double.py

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+def double(value):
+    return value * 2 
+
+
+double("22")
+print(double("22"))
+
+
+# Coming from JS, I predicted that Python might behave the same way.
+# Under the hood, without throwing an error, Python would concatenate
+# the string "22" with itself, and the result would be "2222".
+
+# correction: later on I realised JavaScript and Python behave differently JS coerces so "22" * 2 returns 44 in JS whereas Python repeats the string according to the number, so "22" * 2 returns "2222".
+
+
+def double(number):
+    return number * 3
+
+print(double(10))
+
+# As mentioned in prep section either the name should be triple or the code should be *2 

exercises-sprint5/enums.py

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+"""
+Laptop Library System
+This program helps library users find available laptops matching their
+preferred operating system. It demonstrates enum usage, type safety,
+and input validation.
+"""
+
+
+from dataclasses import dataclass
+from enum import Enum
+from typing import List
+import sys
+
+
+# --------------------------------------------------------------------
+# ENUM DEFINITIONS
+# --------------------------------------------------------------------
+"""
+    Represents valid operating systems for laptops.
+    Using enums prevents string comparison issues (case, typos, spaces).
+"""
+
+class OperatingSystem(Enum):
+    UBUNTU = "Ubuntu"
+    MACOS = "macOS"
+    ARCH = "Arch Linux"
+
+# --------------------------------------------------------------------
+# DATA CLASSES
+# --------------------------------------------------------------------
+#Represents a library user with their preferences.
+
+@dataclass(frozen=True)
+class Person:
+    name: str
+    age: int
+    preferred_operating_systems: OperatingSystem
+
+
+#Represents a laptop available in the library.
+@dataclass(frozen=True)
+class Laptop:
+    id: int
+    manufacturer: str
+    model: str
+    screen_size_in_inches: float
+    operating_system: OperatingSystem
+
+# --------------------------------------------------------------------
+# BUSINESS LOGIC
+# --------------------------------------------------------------------
+"""
+    Filters laptops to find those matching the user's preferred OS.
+
+    Args:
+        laptops: List of available laptops
+        person: User with OS preference
+
+    Returns:
+        List of laptops matching the user's preferred OS
+"""
+def find_possible_laptops(laptops: List[Laptop], person: Person) -> List[Laptop]:
+    possible_laptops = []
+    for laptop in laptops:
+        if laptop.operating_system == person.preferred_operating_systems:
+            possible_laptops.append(laptop)
+    return possible_laptops
+
+
+# --------------------------------------------------------------------
+# MAIN PROGRAM - USER INPUT AND PROCESSING
+# --------------------------------------------------------------------
+# Get user input as strings first (raw input)
+name = input("Enter your name: ")
+age_str = input("Enter your age: ")
+print("Available operating systems: Ubuntu, macOS, Arch Linux")
+os_str = input("Enter your preferred OS (Ubuntu, macOS, or Arch Linux): ")
+
+# --------------------------------------------------------------------
+# INPUT VALIDATION AND CONVERSION
+# --------------------------------------------------------------------
+
+# Convert age from string to integer with error handling
+# Output to stderr as per requirements, exit with non-zero code
+while True:
+    age_str = input("Enter your age: ")
+    try:
+        age = int(age_str)
+        break
+    except ValueError:
+        print(f"Error: {age_str} is not a valid age. Please enter a number.")
+
+# Convert OS string to enum with error handling
+# Convert OS string to enum with error handling
+os = None
+while os is None:
+    try:
+        os = OperatingSystem(os_str) 
+    except ValueError:
+        print(f"Error: '{os_str}' is not a valid OS. Valid options are: Ubuntu, macOS, Arch Linux", file=sys.stderr)
+        os_str = input("Enter preferred OS: ")
+
+
+# Create Person object from validated input
+# Now we know age is a valid int and os is a valid OperatingSystem
+person = Person(name=name, age=age,  preferred_operating_systems=os)
+
+# --------------------------------------------------------------------
+# DATA - AVAILABLE LAPTOPS
+# --------------------------------------------------------------------
+# Pre-defined list of laptops in the library (as per exercise requirements)
+laptops = [
+    Laptop(id=1, manufacturer="Dell", model="XPS", screen_size_in_inches=13, operating_system=OperatingSystem.ARCH),
+    Laptop(id=2, manufacturer="Dell", model="XPS", screen_size_in_inches=15, operating_system=OperatingSystem.UBUNTU),
+    Laptop(id=3, manufacturer="Dell", model="XPS", screen_size_in_inches=15, operating_system=OperatingSystem.UBUNTU),
+    Laptop(id=4, manufacturer="Apple", model="macBook", screen_size_in_inches=13, operating_system=OperatingSystem.MACOS),
+]
+
+
+# --------------------------------------------------------------------
+# PROCESSING - FIND MATCHING LAPTOPS
+# --------------------------------------------------------------------
+# Find laptops matching user's preferred OS
+possible_laptops = find_possible_laptops(laptops, person)
+
+# Requirement: Tell user how many laptops have their OS
+print(f"we have {len(possible_laptops)} laptops with {os.value}")
+
+
+# --------------------------------------------------------------------
+# COUNTING LAPTOPS PER OPERATING SYSTEM
+# --------------------------------------------------------------------
+# Count laptops for each OS to find which has most
+arch_count = 0
+ubuntu_count = 0
+macos_count = 0
+for laptop in laptops:
+    if laptop.operating_system == OperatingSystem.ARCH:
+        arch_count += 1
+    elif laptop.operating_system == OperatingSystem.UBUNTU:
+        ubuntu_count += 1
+    else:
+        macos_count += 1
+
+
+
+
+# --------------------------------------------------------------------
+# FINDING THE OPERATING SYSTEM WITH MOST LAPTOPS
+# --------------------------------------------------------------------
+# Store counts in dictionary for easy max calculation
+os_counts = {
+    OperatingSystem.ARCH: arch_count,
+    OperatingSystem.UBUNTU: ubuntu_count,
+    OperatingSystem.MACOS: macos_count
+}
+
+# Find OS with maximum laptops
+max_os = max(os_counts, key=os_counts.get)  # Gets the OS with highest count
+max_count = os_counts[max_os]  # The actual count
+
+
+# --------------------------------------------------------------------
+# COMPARISON AND SUGGESTION LOGIC
+# --------------------------------------------------------------------
+# Get user's OS choice and count
+os_user= person.preferred_operating_systems
+user_count = os_counts[os_user]
+
+
+
+# Requirement: Suggest alternative if another OS has MORE laptops
+# Check: 1) Different OS, AND 2) Has strictly more laptops (> not >=)
+if os_user != max_os and max_count > user_count:
+    print(f" if you're willing to accept {max_os.value} " +
+          f"you'd have {max_count} laptops available " + 
+          f"(vs {user_count} for {os_user.value})")
+
+
+

exercises-sprint5/generics.py

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+#✍️exercise
+#Fix the above code so that it works. You must not change the print on line 17 - we do want to print the children’s ages. (Feel free to invent the ages of Imran’s children.)
+
+
+
+from dataclasses import dataclass
+
+@dataclass(frozen=True)
+class Person:
+    name: str
+    children: list["Person"]
+    age: int
+
+fatma = Person(name="Fatma", age=7, children=[])
+aisha = Person(name="Aisha", age=10, children=[])
+
+imran = Person(name="Imran",age=50, children=[fatma, aisha])
+
+def print_family_tree(person: Person, level: int = 0) -> None:
+    indent = "  " * level
+    print(f"{indent}{person.name} ({person.age})")
+    for child in person.children:
+        print_family_tree(child, level + 1)
+
+
+print_family_tree(imran)
+
+
+# When I first ran mypy with `children: list`, it found no errors.
+# This is because mypy didn't know what type of items were in the list.
+# After changing to `children: List["Person"]` (using generics), 
+# mypy could identify that each child is a Person object.
+# Now it caught the bug: Person has no "age" attribute.
+# I fixed this by adding `age: int` to the Person class.

exercises-sprint5/inheritance.py

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+""" ✍️exercise
+Play computer with this code. Predict what you expect each line will do. Then run the code and check your predictions. (If any lines cause errors, you may need to comment them out to check later lines).
+"""
+
+# PREDICTION: This defines a base class called Parent
+class Parent:
+     # PREDICTION: Constructor that sets first_name and last_name attributes
+    def __init__(self, first_name: str, last_name: str):
+        self.first_name = first_name
+        self.last_name = last_name
+
+# PREDICTION: Method that returns full name as "first last"
+    def get_name(self) -> str:
+        return f"{self.first_name} {self.last_name}"
+
+
+# PREDICTION: Child class inherits everything from Parent class
+class Child(Parent):
+ # PREDICTION: Constructor calls parent's constructor then adds new attribute    
+    def __init__(self, first_name: str, last_name: str):
+        super().__init__(first_name, last_name) # PREDICTION: Calls Parent.__init__
+        self.previous_last_names = []  # PREDICTION: Creates empty list for this instance
+
+# PREDICTION: Method to change last name and track previous names
+    def change_last_name(self, last_name) -> None:
+        self.previous_last_names.append(self.last_name)
+        self.last_name = last_name
+
+# PREDICTION: Method that returns full name with maiden name note if changed
+    def get_full_name(self) -> str:
+        suffix = ""
+        if len(self.previous_last_names) > 0:
+            suffix = f" (née {self.previous_last_names[0]})"
+        return f"{self.first_name} {self.last_name}{suffix}"
+
+
+# PREDICTION: Creates Child instance with names "Elizaveta" "Alekseeva"
+person1 = Child("Elizaveta", "Alekseeva")
+# PREDICTION: Prints "Elizaveta Alekseeva" (calls inherited get_name() from Parent)
+print(person1.get_name())
+# PREDICTION: Prints "Elizaveta Alekseeva" (no suffix since no name change yet)
+print(person1.get_full_name())
+# PREDICTION: Changes last name to "Tyurina", adds "Alekseeva" to previous_last_names
+person1.change_last_name("Tyurina")
+# PREDICTION: Prints "Elizaveta Tyurina" (updated last name)
+print(person1.get_name())
+# PREDICTION: Prints "Elizaveta Tyurina (née Alekseeva)" (shows maiden name)
+print(person1.get_full_name())
+
+
+# PREDICTION: Creates Parent instance (NOT Child) with same names
+person2 = Parent("Elizaveta", "Alekseeva")
+# PREDICTION: Prints "Elizaveta Alekseeva" (Parent has get_name() method)
+print(person2.get_name())
+# PREDICTION:  ERROR! Parent class doesn't have get_full_name() method
+print(person2.get_full_name())
+# PREDICTION:  ERROR! Parent class doesn't have change_last_name() method
+person2.change_last_name("Tyurina")
+# PREDICTION: Won't reach this line due to previous error
+print(person2.get_name())
+# PREDICTION: Won't reach this line due to previous error
+print(person2.get_full_name())