❔ Question from the interview

What are lambdas and what are their features?

Answer: Lambdas are anonymous functions without a name, which are used for short one-time operations. They consist of a single expression and automatically return its result. Most often, lambdas are passed to the map, filter, and reduce functions when a full function declaration is not required.

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❔ Question from the interview

What is serialization and why is it needed?

Answer: Serialization is the process of converting an object into a stream of bytes or a string in order to save it to a file, transmit it over a network, or store it in a database. In Python, modules such as pickle, json, marshal, etc. are used for this purpose.

A serialized object can then be deserialized — its original structure can be restored in memory. This is necessary when transferring data between programs, caching, or interprocess communication.

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❔ Interview question

What are processes and threads, and what is the difference between them?

Answer: A process is an independent execution unit with its own memory and resources. A thread is a subtask within a process that shares the same memory with other threads.

In Python, threads are limited by the GIL (Global Interpreter Lock) — only one thread can execute bytecode at a time. Therefore, for parallel computing, multiprocessing (which creates separate processes) is used, while threading is mainly applied to tasks where threads often wait, such as network requests or file reading.

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❔ Question from the interview

How does authentication differ from authorization?

Answer: Authentication answers the question of who exactly is accessing the system. At this stage, the user's credentials are checked, such as a login and password, a token, or a certificate.

Authorization takes place after successful authentication and determines what actions this user is allowed to perform: which resources he has access to and what operations he can carry out.

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❔ Interview question

Why is bool([]) — False, and bool([[]]) — True?

Answer: An empty list ([]) is considered logically false, but a list with at least one element (even if it's also empty) is no longer an empty object, and therefore True.

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❔ Question from the interview

How does authentication using a JWT token work?

Answer: After successful verification of the credentials, the server creates a JWT token containing information about the user and its expiration date, and signs it with a secret key or a private key. The token is transmitted to the client and is subsequently sent with every request, usually in the Authorization header.

The server does not store the session state and checks only the signature and validity of the token with each request. This approach is stateless, scales well, and does not require session storage, but it complicates the early revocation of tokens without the use of additional storage.

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❔ Question from the interview

What is the difference between authentication using a JWT token and authentication using a session token stored in Redis?

Answer: With JWT authentication, the server does not store the session state: the token contains the user's data and is verified by its signature and expiration date. This is well-scalable, but it complicates the early revocation of tokens.

When using a session token in Redis, the server stores sessions and checks them with each request. This approach gives full control over sessions and allows them to be immediately disabled, but it requires server storage and additional calls to Redis.

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❔ Interview question

What are lazy calculations?

Answer: Lazy calculations are a technique where values are calculated only as needed, rather than immediately. In Python, this is implemented using generators, iterators, and functions such as range(). They allow saving memory and resources, especially when working with large data sets, as elements are calculated and processed one at a time.

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❔ Interview question

What is GIL in Python, why is it needed, and how can it be bypassed?

Answer: GIL (Global Interpreter Lock) is a mechanism in the CPython interpreter that ensures that only one thread can execute Python bytecode at a time. It was introduced to simplify memory management and ensure thread safety for built-in data structures.

However, due to GIL, multithreading in Python does not provide true parallelism at the CPU level: even if you create multiple threads, they will be executed sequentially, not simultaneously, which limits performance for computationally intensive tasks.

This limitation can be bypassed by using modules like multiprocessing, which launch separate processes with their own memory and their own GIL. You can also move heavy logic into native C extensions or use interpreters without GIL, such as Jython or experimental versions of PyPy.

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➡ @DataScienceQ

This channels is for Programmers, Coders, Software Engineers.

0️⃣ Python
1️⃣ Data Science
2️⃣ Machine Learning
3️⃣ Data Visualization
4️⃣ Artificial Intelligence
5️⃣ Data Analysis
6️⃣ Statistics
7️⃣ Deep Learning
8️⃣ programming Languages

✅ https://news.1rj.ru/str/addlist/8_rRW2scgfRhOTc0

✅ https://news.1rj.ru/str/Codeprogrammer

❔ Question from the interview

What is the difference between remove, del, and pop?

Answer: remove() removes the first matching value; del removes an element by its index; pop() removes an element by its index and returns that element.

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❔ Interview question

Why are metrics needed and what are the main endpoints used for collecting them?

Answer: Metrics are used to monitor the state and behavior of the system in real time. They allow you to track performance, load, the number of errors, resource usage, and identify problems before they affect users. Based on metrics, alerts are set up, degradations are analyzed, the impact of changes is assessed, and informed technical decisions are made.

To collect metrics, a separate HTTP endpoint is usually used /metrics, which provides indicators in a format understandable to monitoring systems, such as Prometheus. In addition to this, service endpoints are often used /health or /healthz to check the status of the service and /ready or /readiness to determine the application's readiness to accept traffic. These endpoints complement the metrics and are used in observability and orchestration systems.

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❔ Question from the interview

What is a generator function?

Answer: A generator function is a function whose body contains the keyword yield. When called, such a function returns a generator object (generator object) (generator iterator).

tags: #article

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❔ Question from the interview

Why are break and continue needed?

Answer: They are used to control the sequence of operations: break stops the execution of the loop and transfers the execution to the next block of code, continue kind of skips to the next iteration of the loop and does not stop its execution.

tags: #interview

➡ @DataScienceQ