Q: What is a dict and what's its most important limitation?

A dict is a structure akin a hash map. It stores key-value pairs, where keys are unique and it has O(1) access time. The most important limitation for a dict is that the keys must be hashable/immutable. Meaning, we can use a tuple as a key, but not a list.

Q: Using list comprehension, print the odd numbers between 0 and 100.

[a for a in range(0, 100) if a%2]

Q: Write a simple decorator.

def paragraph_wrap(func): def func_wrapper(name): return "<p>{0}</p>".format(func(name)) return func_wrapper @paragraph_wrap def get_text(name): return "lorem ipsum, {0} dolor sit amet".format(name) print get_text("John")

Q: Given the list lst = [1, 2, 3, 4, 4, 6, 7, 3, 4, 5, 2, 7] , return only the unique values in the list.

set(lst) - one answer. The limitation of this solution is that values should be hashable. Another answer is to iterate through the list and use an intermediate list to store the current value. Then for every next value, check if it's added already.

Question 1

What's the difference between a tuple and a list?

Accepted Answer

Both tuples and lists are data structures in Python and hold a list of values. Unlike lists, tuples are immutable - they can't be changed.

Question 2

What is a dict and what's its most important limitation?

Accepted Answer

A dict is a structure akin a hash map. It stores key-value pairs, where keys are unique and it has O(1) access time. The most important limitation for a dict is that the keys must be hashable/immutable. Meaning, we can use a tuple as a key, but not a list.

Question 3

What is a "callable"?

Accepted Answer

A callable is an object we can call - function or an object implementing the __call__ special method. Any object can be made callable.

Question 4

Using list comprehension, print the odd numbers between 0 and 100.

Accepted Answer

[a for a in range(0, 100) if a%2]

Question 5

What is pickling/unpickling?

Accepted Answer

Pickling is converting an object to a string representation in python. Generally used for caching and transferring objects between hosts/processes.

Question 6

What's a generator?

Accepted Answer

A generator is a callable object that acts as an iterable (object you can iterate in for cycles etc).

Question 7

Explain the use of decorators.

Accepted Answer

Decorators in Python are used to modify or inject code in functions or classes. Using decorators, you can wrap a class or function method call so that a piece of code can be executed before or after the execution of the original code. Decorators can be used to check for permissions, modify or track the arguments passed to a method, logging the calls to a specific method, etc.

Question 8

Write a simple decorator.

Accepted Answer

def paragraph_wrap(func):
def func_wrapper(name):
return "{0}
".format(func(name))
return func_wrapper
@paragraph_wrap
def get_text(name):
return "lorem ipsum, {0} dolor sit amet".format(name)
print get_text("John")

Question 9

Suppose lst is [2, 33, 222, 14, 25], What is lst[-1]?

Accepted Answer

25. Negative numbers mean that you count from the right instead of the left. So, lst[-1] refers to the last element, lst[-2] is the second-last, and so on.

Question 10

Given the list lst = [1, 2, 3, 4, 4, 6, 7, 3, 4, 5, 2, 7], return only the unique values in the list.

Accepted Answer

set(lst) - one answer. The limitation of this solution is that values should be hashable.
Another answer is to iterate through the list and use an intermediate list to store the current value. Then for every next value, check if it's added already.

Question 11

What's lambda?

Accepted Answer

Lambda in Python is an anonymous function created at runtime. E.g.

greeter = lambda x: "Hello %s" % x
greeter("Deko") #prints Hello Deko

Question 12

Explain *args and **kwargs

Accepted Answer

Although, there is no formal rule on calling them *args/**kwargs, people tend to name them that way. When a function is declared def my_func(*args, **kwargs), args is a tuple with all positional arguments passed to the function and kwargs is a dict with all keyword arguments. They can be named anything as long as the unpack operators * and ** are used.
* unpacks a tuple and ** unpacks a dict.

Question 13

Is this valid in Python and why?

def my_function():
print my_function.what
my_function.what = "right?"
my_function() # Prints "right?"

Accepted Answer

It is valid. In Python, everything is an object, including functions. But if we don't have what defined, we will get an Attribute error.

Question 14

Given variables a and b, switch their values so that b has the value of a, and a has the value of b without using an intermediary variable.

Accepted Answer

a, b = b, a

Question 15

How would you xor in Python?

Accepted Answer

(a and not b) or (not a and b)
bool(a) != bool(b)
bool(a) ^ bool(b)

from operator import xor
xor(bool(a), bool(b))

Question 16

What is introspection/reflection and does Python support it?

Accepted Answer

Introspection is the ability to examine an object at runtime. Python has a dir() function that supports examining the attributes of an object, type() to check the object type, isinstance(), etc.
While introspection is passive examination of the objects, reflection is a more powerful tool where we could modify objects at runtime and access them dynamically. E.g.
setattr() adds or modifies an object's attribute;
getattr() gets the value of an attribute of an object.
It can even invoke functions dynamically - getattr(my_obj, "my_func_name")()

Question 17

One thing about python OOP is that it doesn't support true private attributes/methods. How do we circumvent this limitation?

Accepted Answer

There is a convention if we prefix the name with an underscore, it's considered private.

Question 18

What's a Mixin?

Accepted Answer

Mixin is a concept in Programming in which the class provides functionalities but it is not meant to be used for instantiation. The main purpose of the Mixin is to provide functionalities which are standalone and it would be best if the mixins themselves do not have inheritance with other mixins and also avoid state.

Question 19

What's a metaclass?

Accepted Answer

In Python, everything is an object, including classes. And just like any other object, classes are instances of something - a metaclass. The default metaclass is type.

Question 20

What are the Dunder/Magic/Special methods in Python? Name a few.

Accepted Answer

Dunder (derived from double underscore) methods are special/magic predefined methods in Python, with names that start and end with a double underscore. There's nothing really magical about them. Examples of these include:

__init__ - constructor
__str__, __repr__ - object representation (casting to string, printing)
__len__, __next__... - generators
__enter__, __exit__ - context managers
__eq__, __lt__, __gt__ - operator overloading

Question 21

What is PEP8?

Accepted Answer

PEP8 is a generally recognized style guide for programming in Python. It covers formatting, comments, naming conventions, but also programming recommendations as well as useful tips on various topics. The main aim of PEP8 is to help developers improve code readability, reliability and maintainability.

Question 22

What is pip?

Accepted Answer

Pip is a Python package management system. It provides means of installing, versioning and freezing Python software packages and libraries from the main CheeseShop or third party repositories.

Question 23

CheeseShop? What is that?

Accepted Answer

CheeseShop is what the python developers call PyPI (The Python Package Index) - a repository of software for the Python programming language.

Question 24

What are virtualenvs?

Accepted Answer

A virtualenv is what Python developers call an isolated environment for development, running, debugging Python code. It is used to isolate a Python interpreter together with a set of libraries and settings. Together with pip, it allows us to develop, deploy and run multiple applications on a single host, each with their own version of the Python interpreter, and separate set of libraries.

Question 25

What are modules and packages in Python?

Accepted Answer

A module in Python is any file with .py extension. A package is a set of modules - a directory that contains one or many .py files, one of which is __init__.py
Both modules and packages define functions, classes or any kind of software functionality.
When we import something in Python, we import from packages and modules.

Question 26

Bonus question: Tabs or Spaces?

Accepted Answer

Author is a spaces zealot. 4 spaces per tab that is. Both answers are correct (spaces is more correct ?). Incorrect answers are  "I don't know", "I don't care", "Both", "Does it matter".

26 Essential python

Interview Questions

An updated list of python interview questions that will help companies hire top software developers.

What's the difference between a `tuple` and a `list`?

What is a `dict` and what's its most important limitation?

What is a "callable"?

Using list comprehension, print the odd numbers between 0 and 100.

What is pickling/unpickling?

What's a generator?

Explain the use of decorators.

Write a simple decorator.

Suppose lst is `[2, 33, 222, 14, 25]`, What is `lst[-1]`?

Given the list `lst = [1, 2, 3, 4, 4, 6, 7, 3, 4, 5, 2, 7]`, return only the unique values in the list.

What's lambda?

Explain `*args` and `**kwargs`

Is this valid in Python and why?
`def my_function(): print my_function.what my_function.what = "right?" my_function() # Prints "right?"`

Given variables a and b, switch their values so that b has the value of a, and a has the value of b without using an intermediary variable.

How would you `xor` in Python?

What is introspection/reflection and does Python support it?

One thing about python OOP is that it doesn't support true private attributes/methods. How do we circumvent this limitation?

What's a Mixin?

What's a metaclass?

What are the Dunder/Magic/Special methods in Python? Name a few.

What is PEP8?

What is pip?

CheeseShop? What is that?

What are virtualenvs?

What are modules and packages in Python?

Bonus question: Tabs or Spaces?

Join 5K+ tech leaders

Ready to start?

26 Essential python

Interview Questions

An updated list of python interview questions that will help companies hire top software developers.

What's the difference between a tuple and a list?

What is a dict and what's its most important limitation?

What is a "callable"?

Using list comprehension, print the odd numbers between 0 and 100.

What is pickling/unpickling?

What's a generator?

Explain the use of decorators.

Write a simple decorator.

Suppose lst is [2, 33, 222, 14, 25], What is lst[-1]?

Given the list lst = [1, 2, 3, 4, 4, 6, 7, 3, 4, 5, 2, 7], return only the unique values in the list.

What's lambda?

Explain *args and **kwargs

Is this valid in Python and why?def my_function():print my_function.whatmy_function.what = "right?"my_function() # Prints "right?"

Given variables a and b, switch their values so that b has the value of a, and a has the value of b without using an intermediary variable.

How would you xor in Python?

What is introspection/reflection and does Python support it?

One thing about python OOP is that it doesn't support true private attributes/methods. How do we circumvent this limitation?

What's a Mixin?

What's a metaclass?

What are the Dunder/Magic/Special methods in Python? Name a few.

What is PEP8?

What is pip?

CheeseShop? What is that?

What are virtualenvs?

What are modules and packages in Python?

Bonus question: Tabs or Spaces?

Join 5K+ tech leaders

Ready to start?

What's the difference between a `tuple` and a `list`?

What is a `dict` and what's its most important limitation?

Suppose lst is `[2, 33, 222, 14, 25]`, What is `lst[-1]`?

Given the list `lst = [1, 2, 3, 4, 4, 6, 7, 3, 4, 5, 2, 7]`, return only the unique values in the list.

Explain `*args` and `**kwargs`

Is this valid in Python and why?
`def my_function(): print my_function.what my_function.what = "right?" my_function() # Prints "right?"`

How would you `xor` in Python?