Created by Guido van Rossum and released in 1991, Python is a general-purpose, high-level, object-oriented computer programming language. It runs on different platforms such as Windows, Linux, UNIX, and Macintosh.
One of its main advantages is its high-level built-in data structures, which can be combined with dynamic binding and dynamic typing. Easy to learn and with low coding requirements, Python had been widely used to solve artificial intelligence, data science, and machine learning problems; but also in building operating systems, enterprise and business applications development, games, graphic design applications, GUI-based desktop applications, image processing, language development, mathematics, server-side web development, software development, and system scripting, among others.
Therefore, it is easy to understand why Python Certification is one of the most sought-after skills in programming. So, if you are looking forward to getting a job related to this language, we have selected the most commonly asked Python interview questions and the respective answers, at both basic and advanced levels.
We also had included several Python Code Challenges that will help you to be more prepared for your interview ahead. So when you had mastered our selection, you will be ready to excel in your Python interview.
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Basic Python questions
Is Python a programming or a scripting language?
Although Python is capable of scripting, it is considered as a general-purpose programming language.
What does it mean that Python is an interpreted language?
Any programming language which is not in machine-level code before runtime is an interpreted language, such as Python is.
Explain the key features of Python
Unlike C and its variants, Python does not need to be compiled before it is run, since it is an interpreted language similar to PHP or Ruby. It is also dynamically typed, so we do not need to state the types of variables.
As a programming language, it is well suited to OOP (object-oriented programming). It allows the definition of classes along with inheritance and composition since it does not have access to specifiers. Python defines functions and classes as first-class objects, so they can be assigned to variables and then returned from other functions as well as passed into functions.
A somehow inconvenience is that Python runs slower than compiled languages, but coding with it is faster. Moreover, Python allows the inclusion of C-based extensions (such as the numpy package) to crunch the numbers and speed up the run. Due to these features, Python is commonly used as a “glue” code to integrate other languages and components into an effective solution to difficult problems.
State the benefits of using Python
Python is:
An interpreted language: it executes the code sequentially, line by line, and stops if an error occurs.
Dynamically typed: we do not need to assign data types to variables when coding. They get assigned during runtime.
Easy to use: Nevertheless it is a high-level programming language; Python is easy to learn, read, use and write.
Free and open-source: we can use it and distribute it freely.
Fully portable: Python programs can run directly on almost any platform without any personalization.
It has extensive support for libraries: since Python is an open-source programming language, it has lots of already developed libraries with almost any function implemented. Those libraries can be easily imported using the Python Package Manager.
User friendly: the data structure that Python use is easy to understand and, as a programming language, Python requires less code to provide powerful functionalities.
Mention some web frameworks that use Python to develop web applications
Some of the most popular web frameworks in Python to develop web applications are Django, Flask, and Pyramid.
What is Flask and what are its benefits if compared to Django?
Flask is a web microframework for Python, based on the Werkzeug and Jinja2 dependencies. Flask has no dependencies on external libraries, so it is very light as a framework and had fewer security bugs. Much simpler compared to Django, Flask requires more coding. In Django, there is a lot of prewritten code for users, but technically both are equally good.
What is a Python function?
A function in Python is a section of the program or a code block that can be executed whenever required in the program when written. Essentially, is a block of self-contained statements with a valid name, parameters list, and body. They are used in Python to make programming more functional and modular. We can write new functions and also use the built-in functions provided by Python.
What is namespace in Python?
In Python, a namespace refers to the name assigned to each object, where an object can be a variable or function. So, when an object is created, its name along with space (the address of the outer function where the object is) is also created. Those namespaces are treated in Python as a dictionary, where the key is the namespace and the value is the address of the object.
There are 4 types of namespaces:
Built-in namespace: it contains all the built-in objects in python. It is available whenever python is running.
Global namespace: namespaces for all the objects created on the main program level.
Enclosing namespaces: namespaces at a higher level or in outer functions.
Local namespaces: namespaces at the local or inner function.
Can you explain what a decorator in Python is?
A decorator is used to add a design pattern to a function without changing its structure. They are defined before the function they are enhancing.
To apply a decorator we must define first the decorator function, we code the function it is applied to and then we add the decorator function above the function we want to apply to, using the @ symbol before the decorator.
Mention the common built-in data types in Python
The common built-in data types in Python are:
Boolean: data type with two possible values, true or false.
Dictionary: a data type that stores values in key and value pairs, where the order of items is not important, since each value can be accessed using its key.
List: ordered sequence of items, which can belong to different data types.
Numbers: They include complex numbers, floating-point numbers, and integers.
Set: a non-ordered collection of unique items.
String: sequence of characters, declared within single or double-quotes.
Tuple: ordered sequence of items as the list, but they cannot be changed.
What is an operator in Python?
Operators are particular symbols that, applied to some values, produce an output as a result. They work on operands: numeric literals or variables which hold some values.
An operator can be unary, binary, or ternary, according to how many operands it requires. Then, we can use in Python different types of operators, such as arithmetic, assignment, bitwise, identity, logical, membership, or relational operators.
Advanced Python interview questions
What is a keyword in Python?
Keywords are 33 reserved words with special meaning in Python, most of them used to define the type of variables. They cannot be used as variable or function names:
The 33 keywords in python are: And/ As/ Assert/ Break/ Class/ Continue/ Def/ Del/ Elif/ Else/ Except/ False/ Finally/ For/ From/ Global/ If / Import/ In/ Is/ Lambda/ None/ Nonlocal/ Not/ Or/ Pass/ Raise/ Return/ True/ Try/ While/ With/ and Yield.
What does it mean “type conversion” in Python?
It refers to the conversion of one data type into another, using the following functions:
complex(real,imag): it converts real numbers to complex(real,imag) ones.
dict(): it converts a tuple of order (key,value) into a dictionary.
float(): it converts any data type into float type
hex(): it converts integers to hexadecimal values
int(): it converts any data type into an integer
list(): it is used to convert any data type to a list.
oct(): it converts the integer to octal
ord(): it converts characters into integer
set(): it returns the type after converting to set.
str(): it converts an integer into a string.
tuple():it is used to convert to a tuple.
Explain how Python does compile-time and run-time code checking
At compile time some amount of coding is done, but most of the checking (types, names, etc.) is not completed are until code execution.
Therefore, even when the Python code references a missed user-defined function, the code compilation will be successful. That means that the Python code will not fail until an exception where the code execution path does not exist occurs.
What are python modules?
A Python module is a file containing Python code that can either be function classes or variables. Basically, it is a .py file containing executable code. The commonly used built-in Python modules are data time, JSON, math, os, random, and sys.
What is PYTHONPATH?
It is an environment variable used when a module is imported, to check for the presence of the imported modules in several directories. Then, the interpreter uses it to select which module to load.
Explain what is lambda function in Python
In Python, a lambda function is an anonymous function: a function defined without a name. Normal functions are defined using a keyword "def", while anonymous functions are defined using the “lambda” keyword.
What is a negative index in Python? Why are they used?
The sequences in Python are indexed using both positive and negative numbers. The positive numbers use '0' (as first index) and '1' as the second index and so on.
On the other hand, the index for the negative number starts from '-1', stating that is the last index in the sequence and '-2' as the penultimate index. Then, the sequence goes forward like when we deal with positive numbers.
A negative index is used to remove any new-line spaces from a given string. That allows the string to accept the last character that is given as S[:-1]. Another case where the negative index is used is to represent the string in the correct order.
Explain what is slicing in Python
It is a mechanism used to select a range of items from a sequence type (list, tuple, or string). Slicing requires a : (colon) that marks the start and end index of the field to fetch elements as a group, instead of specifying an index, where we get only a single element.
How is memory managed in Python?
Memory management in Python is done by private heap spaces, where all Python objects and data structures are located. The programmer does not have access to this heap: all memory management is done by the python interpreter. Python also has an inbuilt garbage collector that recycles all the unused memory to make it available to the heap space.
What is Pandas?
Is an open-source python library that supports data structures for data-based operations for data analysis and manipulation. It offers a large set of features to deal with almost any data operation in algorithms or to solve complex business problems. This library helps the programmer to deal with a large number of files where data is stored.
What is GIL and how do we get around it?
GIL is the acronym for Global Interpreter Lock, a mechanism Python is using for concurrency. Its major downside is that it locks the interpreter and threads are not executed at the same time, resulting in performance losses. GIL is built in deep into the Python system, but there are three ways of getting around it for the moment:
Using the multiprocessing module: it spawns new Python processes and manages them as if they were threads
Using the asyncio module: it enables asynchronous programming, adding the async/await syntax and, therefore, making the code way clearer.
Using stackless Python: it is a fork of Python programmed without GIL.
Python Code Challenges
So, with these challenges, we have reached the end of this article on Python Interview Questions. We hope that you feel now more confident and remember: make sure you study and practice as much as possible. Good luck with that interview ahead!
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