Python Technical Interview

📦
Modules & Packages

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What's the difference between a module and a package in Python?

Module: A single Python file (.py) containing code that can be imported directly.

Package: A directory containing multiple modules with an __init__.py file.

# Module example
import utils
from utils import some_function

# Package example  
import data_processing.cleaners
from data_processing import validators
                        

What is the purpose of init.py in a Python package?

The __init__.py file serves multiple purposes:

Marks the directory as a Python package
Contains initialization code that runs when the package is imported
Controls what gets imported with from package import *

_
Single Underscore Usage

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What are the different uses of a single underscore (_) in Python?

The single underscore has several uses:

# 1. Throwaway variable
name, _, age = ("John", "middle", 25)

# 2. Internal use convention
class MyClass:
    def _internal_method(self):
        pass

# 3. Last expression in REPL
>>> 5 + 3
8
>>> _
8

# 4. Internationalization
from gettext import gettext as _
print(_("Hello"))

# 5. Number separator (Python 3.6+)
million = 1_000_000
                        

⚡
Static vs Class Methods

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Explain the difference between @staticmethod and @classmethod decorators

class Person:
    species = "Homo sapiens"
    
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    @staticmethod
    def is_adult(age):
        """No automatic arguments"""
        return age >= 18
    
    @classmethod
    def get_species(cls):
        """Receives class as first argument"""
        return cls.species
    
    @classmethod
    def from_string(cls, person_str):
        """Alternative constructor"""
        name, age = person_str.split('-')
        return cls(name, int(age))

# Usage
Person.is_adult(25)  # Static method
Person.get_species()  # Class method
person = Person.from_string("Bob-25")  # Alt constructor
                        

📊
Python to D3.js Integration

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How would you pass data from Python to D3.js for visualization?

Several approaches for Python to D3.js data flow:

# Python - Generate JSON
import json
import pandas as pd

df = pd.DataFrame({
    'name': ['Alice', 'Bob', 'Charlie'],
    'value': [30, 45, 25]
})

# Save as JSON
with open('data.json', 'w') as f:
    json.dump(df.to_dict('records'), f)

# Flask API endpoint
@app.route('/api/data')
def get_data():
    return jsonify(df.to_dict('records'))
                        

// D3.js - Load and use data
d3.json("data.json").then(function(data) {
    // Create visualization
    d3.select("svg")
        .selectAll("rect")
        .data(data)
        .enter()
        .append("rect")
        .attr("height", d => d.value);
});
                        

🔄
Django Middleware

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What is the purpose of middleware in Django?

Middleware are processing layers that sit between the web server and Django application, handling requests and responses globally.

# Custom middleware example
class CustomMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        # Process request before view
        print(f"Request: {request.path}")
        
        response = self.get_response(request)
        
        # Process response after view
        print(f"Response: {response.status_code}")
        return response
                        

Common uses: Authentication, CORS, logging, caching, security headers

Python Technical Interview

📦 Modules & Packages

What's the difference between a module and a package in Python?

What is the purpose of __init__.py in a Python package?

_ Single Underscore Usage