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**Inversion of Control (IoC)** reduces coupling between components by **separating an object's logic from the creation and management of its dependencies**. This is achieved because the object no longer knows **who** and **how** creates the dependencies it needs - it simply receives them "ready-made" through interfaces or external mechanisms (a framework, a container).

---

### 1. Before: tight coupling

Without IoC, each component creates its own dependencies:

```python
class UserService:
    def __init__(self):
        self.repository = UserRepository()
```

The problem:

- `UserService` depends **on the concrete class** `UserRepository`.
- If the implementation needs to be replaced (for example, with `CachedUserRepository`), the code of `UserService` has to change.
- `UserService` cannot be tested in isolation, because it always creates a specific repository.

This is **tight coupling** - the classes are "glued" to each other.

---

### 2. After applying IoC: loose coupling

With IoC, dependencies are **injected from outside**, usually through the constructor:

```python
class UserService:
    def __init__(self, repository):
        self.repository = repository
```

Now `UserService` only knows **that** it needs an object with a `find_by_id` method, not **which one exactly**.
A container or external code decides which implementation to plug in, for example:

```python
user_service = UserService(CachedUserRepository())
```

The result:

- The `UserService` class does not depend on specific implementations.
- It can be tested by plugging in a fake repository.
- The storage logic can be changed without changing `UserService`.

---

### 3. IoC and abstractions

IoC forces modules to depend **on abstractions**, not on details.
For example:

```python
class Repository(Protocol):
    def find_by_id(self, user_id): ...

class UserService:
    def __init__(self, repository: Repository):
        self.repository = repository
```

Now both `UserService` and the various `Repository` implementations depend on a single abstraction.
This removes direct connections between the layers of the system.

---

### 4. Effect on the architecture

IoC makes the system **modular**:

- Components can be changed independently.
- It is easier to add new implementations (for example, a repository for another database).
- The number of changes needed when modifying code decreases (localization of changes).
- Testability increases: "stubs" or "mocks" can be plugged in.

---

### 5. Practical consequence

When IoC is used:

- **Dependencies are inverted**: the code does not call the infrastructure, the infrastructure injects dependencies into the code.
- Each component is responsible only for **its own logic**, without worrying about creating or configuring other parts.
- Coupling drops from *"A knows B"* to *"A knows only the abstraction, not the concrete B"*.

---

**Summary:**
*IoC reduces coupling between components because objects no longer create or manage their own dependencies. Instead, they work through abstractions, and specific implementations are supplied from outside. This weakens connections, simplifies replacing components, and increases the system's flexibility and testability.*

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