Question 1

What is a variable in Python?

Accepted Answer

A variable in Python is a name that refers to a memory location containing a value. Unlike other languages, Python uses dynamic typing: the variable type is automatically determined during assignment. There is no need to explicitly declare the type.

Question 2

What is a class in Python?

Accepted Answer

A class is a blueprint for creating objects that share the same attributes and methods. It defines the structure and behavior of objects that will be instantiated from it. Classes allow organizing code in a modular and reusable way by grouping related data and functionality together.

Question 3

What is the fundamental difference between a list and a tuple in Python?

Accepted Answer

Lists are mutable (can be modified after creation) while tuples are immutable (cannot be modified). This immutability makes tuples hashable and usable as dictionary keys, unlike lists. Tuples are also slightly more performant in terms of memory usage and access speed.

Question 4

What is Git?

Accepted Answer

Git is a distributed version control system created by Linus Torvalds in 2005. Unlike centralized systems like SVN, each developer has a complete copy of the project history locally. This allows working offline and offers great flexibility for collaborative workflows.

Question 5

Which method allows applying multiple different aggregation functions to a single column with groupby?

Accepted Answer

The agg() (or aggregate()) method allows applying multiple aggregation functions to the same columns. You can pass a list of functions like ['sum', 'mean', 'count'] or a dictionary to specify different functions per column. This flexibility is essential for creating comprehensive statistical reports in a single operation.

Question 6

What is the main difference between the pyplot interface and the object-oriented interface in Matplotlib?

Accepted Answer

The pyplot interface (plt.plot, plt.title) is a MATLAB-style API that implicitly manages current figures and axes, convenient for quick simple plots. The object-oriented interface (fig, ax = plt.subplots()) gives explicit control over each element (Figure, Axes) and is recommended for complex plots, multiple subplots, or production scripts, as it makes code more readable and maintainable.

Question 7

What is the main difference between Plotly Express and Plotly Graph Objects?

Accepted Answer

Plotly Express is a high-level API that allows creating charts in a single line of code with simple parameters. Plotly Graph Objects is the low-level API offering complete control over every chart element. Plotly Express uses Graph Objects internally, which allows switching between them to further customize charts.

Question 8

What is a perceptron in the context of neural networks?

Accepted Answer

A perceptron is the basic unit of a neural network, inspired by biological neurons. It takes multiple inputs, multiplies them by weights, sums everything with a bias, then applies an activation function to produce an output. The simple perceptron can only solve linearly separable problems, which led to the development of multilayer networks.

Question 9

What is the main difference between Keras Sequential API and Functional API?

Accepted Answer

Sequential API allows creating models layer by layer in a linear fashion, where each layer has exactly one input and one output. Functional API offers more flexibility by enabling complex architectures: multiple inputs, multiple outputs, residual connections, and shared layer graphs. Use Sequential for simple architectures and Functional for more advanced cases.

Question 10

What is a convolution operation in a CNN?

Accepted Answer

A convolution is a mathematical operation that applies a filter (kernel) over an image by sliding this filter across the input and computing the dot product at each position. This allows extracting local features such as edges, textures, or patterns. Unlike dense networks where each neuron is connected to all inputs, convolution exploits the spatial structure of images by sharing filter weights across the entire image.

Data Science & ML interview questions

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