CCNA Devnet Software Dev Questions

Event-driven architecture (D) is the correct answer because it is inherently asynchronous and decoupled: services communicate by publishing events to a message broker (e.g., Kafka, RabbitMQ) without needing to know about the consumers. This pattern allows the producer to emit an event and continue processing immediately, while consumers react to events at their own pace, achieving loose coupling and high scalability.

Accessing a dictionary key that does not exist raises a KeyError in Python. In the code, my_dict['b'] attempts to retrieve the value for key 'b', which is not present in the dictionary {'a': 1}, so Python raises KeyError.

Option C is correct because `git pull --rebase origin main` fetches the latest changes from the remote `main` branch and then rebases the current `feature-login` branch onto those changes. This incorporates the new commits from `main` without creating a merge commit, resulting in a linear history. The `--rebase` flag ensures that the developer's commits are replayed on top of the updated `main`, avoiding the extra merge commit that `git merge` would create.

Option B is correct because the `timeout` parameter in the requests library allows you to specify a maximum wait time (in seconds) for each request, directly addressing requirement (1) for a variable timeout. Option E is correct because the `headers` parameter is the standard way to include an authorization token (e.g., `{'Authorization': 'Bearer <token>'}`) in every request, satisfying requirement (2). Both features are essential for controlling request behavior and authentication in REST API calls.

In Python, the **kwargs syntax allows a function to accept a variable number of keyword arguments by collecting them into a dictionary. This is the correct parameter syntax for handling arbitrary keyword arguments, as specified in Python's function definition rules.

Option A (except) is correct because it is the block that catches exceptions raised during execution of the try block. Without an except clause, any error would propagate unhandled and crash the program. In file I/O, this is essential to catch specific exceptions like FileNotFoundError or PermissionError and respond appropriately.

Option A is correct because `requests.exceptions.ConnectionError` is raised when a network connection cannot be established, such as DNS resolution failure or refused TCP connection. This is a fundamental network error that must be handled in any HTTP client to ensure robust error recovery.

Option A is correct because `response.raise_for_status()` is a built-in method of the `requests` library that automatically raises an `HTTPError` exception for any 4xx or 5xx status code. This allows the script to handle HTTP errors in a structured way using try/except blocks, rather than manually checking each status code. It is a best practice for robust REST API interaction in Python.

Option D is correct because `git checkout feature-x` is the traditional Git command that switches the HEAD reference to the existing branch 'feature-x' and updates the working directory to match that branch's commit history. This command performs both the branch switch and the working tree update in one operation, which is the core requirement of the question.

HTTP 201 Created is the standard response for a successful POST that creates a resource.

The code modifies each element by adding 1. So [1,2,3] becomes [2,3,4].

Microservices are independently deployable, scalable, and developed by small teams, whereas a monolith is a single deployable unit.

Option C (429 Too Many Requests) is correct because RFC 6585 defines this status code specifically for cases where a client has sent too many requests in a given time frame, exceeding the API's rate limit. REST APIs use this response to enforce throttling and inform the client to back off, often including a Retry-After header to indicate when to retry.

GraphQL allows querying specific data, uses a single endpoint, and provides a schema.

Option C is correct because it uses *endpoints to accept a variable number of positional arguments (the API endpoint strings) and **options to accept any number of keyword arguments (like timeout=30). This matches the requirement for a function that can handle multiple sources with optional parameters, following Python's standard *args/**kwargs pattern.

json.load() reads the file and returns a dict; then accessing the nested structure yields 'GigabitEthernet0/1'.

git checkout -b <branch> creates and switches. git branch <branch> creates but does not switch. git switch -c is also valid but not listed.

204 No Content means the request succeeded, but there is no response body (common for PUT or DELETE).

A is correct because feature branches isolate new work from the stable main branch, enabling parallel development without disrupting the shared codebase. This practice aligns with Git's branching model and supports code review and continuous integration workflows.

json.loads converts to dict, then access scores list index 1.

PUT is idempotent (same result multiple times) but not safe (modifies resource). GET is safe. DELETE is idempotent.

*args captures positional arguments as tuple (1,2,3), sum is 6, kwargs dict includes {'offset':10}, .get returns 10, total 16.

The 201 Created status code is the correct response for a POST request that successfully creates a new resource. According to RFC 7231, the server should respond with 201 and include a Location header pointing to the newly created resource's URI. This is the standard behavior for RESTful APIs when a POST operation results in resource creation.

Squash merging combines all commits into one; using --squash option on merge accomplishes this.

The 'for item in list' loop iterates directly over each element, making it the simplest and most readable for processing each hostname.

Option A is correct because it directly translates the list comprehension into an equivalent for-loop with a conditional append. The comprehension `[x**2 for x in range(20) if x % 2 == 0]` iterates over numbers 0–19, filters for even numbers (x % 2 == 0), squares each, and collects the results in a list. Option A's explicit loop and conditional produce the exact same sequence of appended values.

A 201 status indicates successful creation, and response.json() parses the JSON body into a Python dict.

PATCH is used for partial updates, PUT for full replacement.

json.loads() converts a JSON string into a Python object (dict, list, etc.).

A 429 status code indicates the client has sent too many requests in a given amount of time (rate limiting). The HTTP specification (RFC 6585) recommends including a Retry-After header in the response, which tells the client how long to wait before retrying. Implementing a wait based on this header and then retrying is the correct and respectful way to handle rate limiting, allowing the script to eventually succeed without overwhelming the server.

Option B is correct because `requests.exceptions.ConnectionError` is specifically raised when the underlying TCP connection fails, which includes scenarios like DNS resolution failures, refused connections, or the remote host being unreachable. This exception is a subclass of `RequestException` and directly maps to network-level issues at the transport layer, making it the precise exception to catch for connectivity problems.

Microservices architecture enables each service to be deployed, updated, and scaled independently without affecting other services. This is a key advantage over monolithic architectures, where any change requires rebuilding and redeploying the entire application. For a network monitoring application, independent scalability allows resource-intensive services (e.g., packet capture) to scale separately from lightweight services (e.g., alerting).

GitFlow is a valid branching strategy that defines a strict model for managing releases, hotfixes, and feature development using dedicated branches like 'develop', 'release/*', and 'hotfix/*'. It is widely used in enterprise environments to maintain a clean history and support parallel development.

Option A is correct because Python's `except` clause uses the `as` keyword to bind the exception instance to a variable, allowing access to the error message via `e`. This syntax is valid and commonly used for logging or inspecting exception details.

The MVC pattern explicitly separates an application into three interconnected components: Model (data and business logic), View (user interface), and Controller (handles user input and updates the Model/View). This is the foundational architectural pattern for many web frameworks like Django, Ruby on Rails, and Spring MVC, where the Controller receives HTTP requests, interacts with the Model, and selects the appropriate View for rendering.

Implement retry with exponential backoff to respect rate limiting.

PATCH is used for partial updates to a resource, while PUT replaces the entire resource.

Option B (list) is correct because Python's built-in list type is a mutable, ordered collection that can hold heterogeneous elements and is a fundamental data type in the language. Option D (dict) is correct because dict is a built-in mapping type that stores key-value pairs with unique keys, making it a core Python data type.

GitFlow is correct because it defines a long-lived 'develop' branch for integrating feature branches, and a separate 'release' branch for preparing releases. This strategy uses dedicated branches for features, releases, and hotfixes, with strict merging rules back to 'develop' and 'main'.

Using the json module and context manager is the standard approach; the nested key is accessed via dictionary indexing.

git reset --soft and git revert can be used; soft reset moves HEAD back but keeps changes staged; revert creates new commits undoing changes.

The --oneline flag condenses each commit to a single line showing the commit hash and message.

Using time.time() before and after the request and subtracting gives the elapsed time in seconds.

Option A is correct because it uses the `with` statement, which is a context manager that automatically calls `f.close()` when the block exits, ensuring the file is properly closed even if an exception occurs. The `'r'` mode opens the file for reading, and `f.read()` reads the entire contents into the `data` variable.

Option A is correct because it uses list comprehension syntax with `x**2` to square each number, iterates over `range(11)` to include numbers 0 through 10, and applies the condition `if x % 2 == 0` to filter only even numbers. This produces the list `[0, 4, 16, 36, 64, 100]` as required.

The correct way is to use json parameter for JSON body and headers for authorization.

The list comprehension filters items based on the condition and produces a new list.

A 403 Forbidden status code indicates that the server understood the request but refuses to authorize it. In the context of a REST API requiring authentication, this typically means the authentication token is missing, expired, or invalid, and the server is explicitly denying access. This aligns with RFC 7231, which defines 403 as a response when the server 'refuses to fulfill the request' due to insufficient authorization credentials.

Feature branching (C) is a valid Git branching strategy where each new feature is developed in its own branch, allowing isolated work without disrupting the main codebase. GitFlow (E) is another valid strategy that defines a strict branching model with master, develop, feature, release, and hotfix branches, commonly used for projects with scheduled releases.

The event-driven architecture is correct because it enables asynchronous, decoupled communication between services. When a new device is discovered, an event (e.g., a message on a message broker like Kafka or RabbitMQ) is published, and multiple subscriber services (inventory, monitoring, logging) react independently without blocking the discovery service. This pattern directly supports the requirement for loose coupling and asynchronous notification.

GraphQL allows querying exactly needed data, uses a single endpoint, and clients specify fields.

The correct approach is to open the file with a context manager, read its contents, and use json.loads() to convert the JSON string to a dictionary.

In Python, a set is the correct data type for representing an unordered collection of unique elements. Sets automatically enforce uniqueness by using a hash table internally, so duplicate values are ignored upon insertion. This makes them ideal for operations like membership testing and deduplication, where order is irrelevant.

Option D is correct because in Python, the `*args` syntax in a function definition allows the function to accept a variable number of positional arguments. The asterisk (`*`) collects all extra positional arguments into a tuple named `args`, enabling flexible argument handling.

The json= parameter automatically serializes the Python dictionary to JSON and sets the Content-Type header to application/json.

201 Created is the standard response for a successful POST that creates a new resource.

The 'git checkout -b <branch>' command creates a new branch and switches to it immediately.

According to the REST API conventions, a successful POST request returns status code 201 Created.

Option B is correct because RESTful APIs use standard HTTP methods (GET, POST, PUT, PATCH, DELETE) to map directly to CRUD (Create, Read, Update, Delete) operations. For example, POST creates a resource, GET retrieves it, PUT/PATCH updates it, and DELETE removes it, aligning with the REST architectural constraint of uniform interface.

Event-driven architecture promotes loose coupling, scalability, and real-time responsiveness.

400 Bad Request and 404 Not Found are both client error statuses (4xx).

The params parameter accepts a dict; also can pass dict directly.

Option C is correct because it constructs the Authorization header using the 'Bearer' scheme, which is the standard method for passing OAuth 2.0 bearer tokens in HTTP requests. The requests library requires the header to be explicitly set as a dictionary, and the token must be prefixed with 'Bearer ' to comply with RFC 6750.

Option A is correct because the 'with' statement in Python implements a context manager that automatically calls the file object's __exit__ method when the block exits, ensuring the file is closed even if an exception occurs. This prevents resource leaks and is the recommended pattern for file I/O in Python, as explicitly calling f.close() may be skipped if an exception is raised before the close call.

MVC separates Model (data), View (UI), Controller (logic). Controller updates Model, View reflects Model.

A set is the correct choice because it is implemented as a hash table in Python, which provides O(1) average-time complexity for membership tests using the `in` operator. Sets automatically enforce uniqueness, meaning duplicate items are not allowed, making them ideal for storing a collection of distinct elements. This directly matches the requirement for fast membership testing and uniqueness.

Option B is correct because using square bracket notation (config['timeout']) on a dictionary will raise a KeyError if the specified key does not exist. This is a fundamental behavior of Python dictionaries: direct key access without a fallback mechanism throws an exception when the key is missing.

Option C (Dictionary) is correct because dictionaries in Python are mutable (you can add, remove, or change key-value pairs) and unordered (prior to Python 3.7, insertion order was not guaranteed; even with order preservation in CPython 3.7+, the data structure is conceptually unordered and accessed by key, not index). This matches the question's requirement for a mutable and unordered data type.

In the MVC pattern, the Controller is the component that receives user input (e.g., HTTP requests, button clicks) and translates it into commands that update the Model. It acts as the intermediary between the View and the Model, ensuring that user actions trigger appropriate changes in the application's data layer.

Both `git checkout -- <file>` and `git restore <file>` discard unstaged local changes to a file, reverting it to the content of the last commit (HEAD). `git checkout -- <file>` is the traditional command, while `git restore <file>` is the newer, more intuitive alternative introduced in Git 2.23. Both operate on the working tree without affecting the staging area or commit history.

Option C is correct because the **kwargs syntax in a Python function definition collects any number of keyword arguments into a dictionary. The function then prints that dictionary, which matches the requirement to accept and print any number of keyword arguments.

Microservices allow independent deployment and scaling of services, which is a key advantage.

Option A is correct because it uses the `.items()` method to iterate over key-value pairs, explicitly checks `if ip != None` to skip entries with `None`, and uses an f-string for clean output. This directly meets the requirement to skip `None` values while printing each interface name and IP address.

The list comprehension `[x*2 for x in range(10) if x > 5]` iterates over `x` from 0 to 9, filters to only include `x` values greater than 5 (i.e., 6, 7, 8, 9), and multiplies each by 2, producing `[12, 14, 16, 18]`. This is a standard Python comprehension with a conditional filter.