London | 26-March-SDC | Ammad Ur Rehman | Sprint 5 | Prep Exercises

prep exercises/Classes and objects exercise 1.py

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+class Person:
+    def __init__(self, name: str, age: int, preferred_operating_system: str):
+        self.name = name
+        self.age = age
+        self.preferred_operating_system = preferred_operating_system
+
+imran = Person("Imran", 22, "Ubuntu")
+print(imran.name)
+# print(imran.address) # error: "Person" has no attribute "address"  [attr-defined]
+
+eliza = Person("Eliza", 34, "Arch Linux")
+print(eliza.name)
+# print(eliza.address) # error: "Person" has no attribute "address"  [attr-defined]
+
+def is_adult(person: Person) -> bool:
+    return person.age >= 18
+
+print(is_adult(imran))
+
+def no_attribute_exists(person: Person):
+    print(person.dob)
+
+# mypy detects that dob attribute doesn't exist.
+# error: "Person" has no attribute "dob"  [attr-defined]

prep exercises/Dataclasses exercise.py

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+from dataclasses import dataclass
+from datetime import date
+
+@dataclass(frozen=True)
+class Person:
+    name: str
+    date_of_birth: date
+    preferred_operating_system: str
+
+    def is_adult(self):
+        today = date.today()
+        age = today.year - self.date_of_birth.year
+
+        if (today.month, today.day) < (self.date_of_birth.month, self.date_of_birth.day):
+            age -= 1
+
+        return age >= 18
+
+imran = Person("Imran", date(2004, 6, 28), "Ubuntu")  # We can call this constructor - @dataclass generated it for us.
+print(imran)  # Prints Person(name='Imran', age=22, preferred_operating_system='Ubuntu')
+
+imran2 = Person("Imran", date(2004, 6, 28), "Ubuntu")
+print(imran == imran2)  # Prints True

prep exercises/Enums exercise.py

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+from dataclasses import dataclass
+from enum import Enum
+from typing import List
+import sys
+
+class OperatingSystem(Enum):
+    MACOS = "macos"
+    ARCH = "arch linux"
+    UBUNTU = "ubuntu"
+
+@dataclass(frozen=True)
+class Person:
+    name: str
+    age: int
+    preferred_operating_system: OperatingSystem
+
+
+@dataclass(frozen=True)
+class Laptop:
+    id: int
+    manufacturer: str
+    model: str
+    screen_size_in_inches: float
+    operating_system: OperatingSystem
+
+
+def find_possible_laptops(laptops: List[Laptop], person: Person) -> List[Laptop]:
+    possible_laptops = []
+    for laptop in laptops:
+        if laptop.operating_system == person.preferred_operating_system:
+            possible_laptops.append(laptop)
+    return possible_laptops
+
+
+people = [
+    Person(name="Imran", age=22, preferred_operating_system=OperatingSystem.UBUNTU),
+    Person(name="Eliza", age=34, preferred_operating_system=OperatingSystem.ARCH),
+]
+
+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),
+]
+
+name = input("Please enter your name: ")
+
+def get_age() -> int:
+    while True:
+        try:
+            age_string = input("Please enter your age, you must be >= 18 years old: ")
+            age = int(age_string)
+
+            if age < 18:
+                print("You must be 18+.")
+                continue
+
+            return age
+        except ValueError:
+            print("Please enter a valid number.")
+
+age = get_age()
+
+def get_preferred_operating_system() -> OperatingSystem:
+    while True:
+        preferred_operating_system_input = input("Your preferred operating system (macOS, Ubuntu or Arch Linux): ")
+
+        try:
+            normalised_value = preferred_operating_system_input.strip().lower()
+            operating_system = OperatingSystem(normalised_value)
+            return operating_system
+        except ValueError:
+            print(f"Sorry, we don't have {preferred_operating_system_input}. Please choose from macOS, Ubuntu or Arch Linux.")
+
+operating_system = get_preferred_operating_system()
+
+person = Person(name=name, age=age, preferred_operating_system=operating_system)
+people.append(person)
+
+def find_laptop() -> None:
+    matching_laptops = []
+    non_matching_laptops = []
+
+    for laptop in laptops:
+        if laptop.operating_system == person.preferred_operating_system:
+            matching_laptops.append(laptop)
+        else:
+            non_matching_laptops.append(laptop)
+
+    if matching_laptops:
+            count = len(matching_laptops)
+            print(f"Congratulations, we have found {count} matching laptops!")
+
+            other_laptops_count = len(non_matching_laptops)
+
+            if other_laptops_count > count:
+                print(f"We have found {other_laptops_count} laptops with other operating systems. You might be interested in switching to a different operating system.")
+
+            sys.exit(0)
+    else:
+        sys.exit("Sorry, we couldn't find any matching laptops!")
+
+
+find_laptop()

prep exercises/Generics exercise.py

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+from dataclasses import dataclass
+from typing import List
+
+@dataclass(frozen=True)
+class Person:
+    name: str
+    age: int
+    children: List["Person"]
+
+fatma = Person(name="Fatma", age=7, children=[])
+aisha = Person(name="Aisha", age=11, children=[])
+
+imran = Person(name="Imran", age=32, children=[fatma, aisha])
+
+def print_family_tree(person: Person) -> None:
+    print(person.name)
+    for child in person.children:
+        print(f"- {child.name} ({child.age})")
+
+print_family_tree(imran)

prep exercises/Inheritance.py

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+class Parent:
+    def __init__(self, first_name: str, last_name: str):
+        self.first_name = first_name
+        self.last_name = last_name
+
+    def get_name(self) -> str:
+        return f"{self.first_name} {self.last_name}"
+
+
+class Child(Parent):
+    def __init__(self, first_name: str, last_name: str):
+        super().__init__(first_name, last_name)
+        self.previous_last_names = []
+
+    def change_last_name(self, last_name) -> None:
+        self.previous_last_names.append(self.last_name)
+        self.last_name = last_name
+
+    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}"
+
+person1 = Child("Elizaveta", "Alekseeva")
+print(person1.get_name()) # Should print Elizaveta Actual: Elizaveta Alekseeva
+print(person1.get_full_name()) # Should print Elizaveta Alekseeva
+person1.change_last_name("Tyurina")
+print(person1.get_name()) # Should print Elizaveta Actual: Elizaveta Tyurina
+print(person1.get_full_name()) # Should print Elizaveta Alekseeva (née Tyurina) Actual: Elizaveta Tyurina (née Alekseeva)
+
+person2 = Parent("Elizaveta", "Alekseeva")
+print(person2.get_name()) # Should print Elizaveta Alekseeva
+# print(person2.get_full_name()) # Method doesn't exist because only Child class has it.
+# person2.change_last_name("Tyurina") # Method doesn't exist because only Child class has it.
+print(person2.get_name()) # Should print Elizaveta Alekseeva
+# print(person2.get_full_name()) # Method doesn't exist because only Child class has it.

prep exercises/Methods exercise 1

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+The advantage of a method as a opposed to freestanding function is that it works on the instance of a type.
+The freestanding function knows nothing about the instance of the type because it doesn't belong to a type.
+On an instance, the method can influence the internal states.
+However freestanding function can only work on public APIs whereas instance methods have access to internal APIs.

prep exercises/Methods exercise 2.py

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+from datetime import date
+
+class Person:
+    def __init__(self, name: str, date_of_birth: date, preferred_operating_system: str):
+        self.name = name
+        self.date_of_birth = date_of_birth
+        self.preferred_operating_system = preferred_operating_system
+
+    def is_adult(self):
+        today = date.today()
+        age = today.year - self.date_of_birth.year
+
+        if (today.month, today.day) < (self.date_of_birth.month, self.date_of_birth.day):
+            age -= 1
+
+        return age >= 18
+
+imran = Person("Imran", date(2004, 6, 28), "Ubuntu")
+print(imran.is_adult())

prep exercises/Type checking with mypy exercise.py

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+def open_account(balances: dict[str, float], name: str, amount: float) -> None:
+    balances[name] = amount
+
+def sum_balances(accounts: dict[str, float]) -> float:
+    total: float = 0
+
+    for name, pence in accounts.items():
+        print(f"{name} had balance {pence}")
+        total += pence
+
+    return total
+
+def format_pence_as_string(total_pence: float) -> str:
+    if total_pence < 100:
+        return f"{total_pence}p"
+
+    pounds = int(total_pence / 100)
+    pence = int(total_pence % 100)
+
+    return f"£{pounds}.{pence:02d}"
+
+balances: dict[str, float] = {
+    "Sima": 700,
+    "Linn": 545,
+    "Georg": 831,
+}
+
+open_account(balances, "Tobi", 9.13)
+open_account(balances, "Olya", 7.13)
+
+total_pence = sum_balances(balances)
+total_string = format_pence_as_string(total_pence)
+
+print(f"The bank accounts total {total_string}")

prep exercises/Type-guided refactorings exercise.py

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+from dataclasses import dataclass
+from typing import List
+
+@dataclass(frozen=True)
+class Person:
+    name: str
+    age: int
+    preferred_operating_systems: List[str]
+
+
+@dataclass(frozen=True)
+class Laptop:
+    id: int
+    manufacturer: str
+    model: str
+    screen_size_in_inches: float
+    operating_system: str
+
+
+def find_possible_laptops(laptops: List[Laptop], person: Person) -> List[Laptop]:
+    possible_laptops = []
+    for laptop in laptops:
+        if laptop.operating_system in person.preferred_operating_systems:
+            possible_laptops.append(laptop)
+    return possible_laptops
+
+
+people = [
+    Person(name="Imran", age=22, preferred_operating_systems=["Ubuntu"]),
+    Person(name="Eliza", age=34, preferred_operating_systems=["Arch Linux"]),
+]
+
+laptops = [
+    Laptop(id=1, manufacturer="Dell", model="XPS", screen_size_in_inches=13, operating_system="Arch Linux"),
+    Laptop(id=2, manufacturer="Dell", model="XPS", screen_size_in_inches=15, operating_system="Ubuntu"),
+    Laptop(id=3, manufacturer="Dell", model="XPS", screen_size_in_inches=15, operating_system="ubuntu"),
+    Laptop(id=4, manufacturer="Apple", model="macBook", screen_size_in_inches=13, operating_system="macOS"),
+]
+
+for person in people:
+    possible_laptops = find_possible_laptops(laptops, person)
+    print(f"Possible laptops for {person.name}: {possible_laptops}")

prep exercises/Why we use types exercise 1.py

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+def double(value):
+    return value * 2
+
+# I predict that double("22") will produce 22.0
+
+result = double("22")
+print(result) # Actual result is 2222
+
+# This is because the string is duplicated twice, "22" + "22" = "22" * 2, it is repeating the a sequence of string.

prep exercises/Why we use types exercise 2.py

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+def double(number):
+    return number * 3
+
+print(double(10))
+
+# There are two possible ways to fix the bug.
+
+# 1. The function name is wrong, it needs to be named to triple
+# 2. Or the function name is correct but the calculation is wrong, it should be return * 2
+
+def double(number):
+    return number * 2
+
+value = 10
+print(double(value))