Python

Question 1

What does this operator do %?

Answer 1

returns a remainder

Question 2

What does this operator do //?

Answer 2

math.floor(a / b)

Question 3

What happens when a subclass inherits from a base class?

Answer 3

The subclass inherits all the methods, properties, and attributes of the base class.

Question 4

What are some of the features/advantages of python

Answer 4

Supports multiple inheritance.

Question 5

What is multiple inheritance?

Answer 5

Multiple inheritance is the ability to derive a class from multiple base classes at the same time. Multiple inheritance has a bad reputation to the extent that most modern programming languages don’t support it. Instead, modern programming languages support the concept of interfaces. In those languages, you inherit from a single base class and then implement multiple interfaces, so your class can be re-used in different situations.

Question 6

what is pythons MRO?**Hint multiple inheritance

Answer 6

Method resolution order. The MRO shows the order of classes in which Python is going to look for a matching attribute or method. it can be accessed on the class attribute .__mro__ we can use this to troubleshoot multiple inheritance problems.

Question 7

What are some disadvantages of multiple inheritance?

Answer 7

1) We can end up creating tightly coupled relationships that become too dependent on each other. 2) Create complex relationships between classes that become hard to follow and debug. 3) It can create redundancy if two classes inherit from the same base class. The opposite approach would be to do a composition design. loosely coupled, flexible design.

Question 8

What is __str__( ) method in python?

Answer 8

It provides a verbose, readable string representation of your class. invoked when print( ). is called with an object. it’s considered unofficial documentation str() is used for creating output for end-user while repr() is mainly used for debugging and development. repr’s goal is to be developer-friendly and ideally shows how to recreate the object and str’s meant to be user friendly and readable

Question 9

What is Liskovs substitution principle in relation to python?**HINT THIS HAS TO DO WITH INHERITANCE.

Answer 9

Liskov’s substitution principle is the most important guideline to determine if inheritance is the appropriate design solution. Inheritance should only be used to model an “is a” relationship. Liskov’s substitution principle says that an object of type Derived, which inherits from Base, can replace an object of type Base without altering the desirable properties of a program.

Question 10

what is the __dict__ attribute in python?

Answer 10

Creating a class implicitly inherents from object . __dict__ is one of the members of the object class and is basically. a mapping of all the attributes in an object to their value.

Question 11

What does dictionary comprehension syntax look like?

Answer 11

{i : chr(65+i) for i in range(4)}

Question 12

what’s the difference between item( ) and iteritem( ) on a python dictionary?

Answer 12

The difference only matters In python 2. in python 3 items( ) Return an iterator over the dictionary’s (key, value) pairs. we use this to iterate over the dictionary

Question 13

When should you use inheritance? When should you use them over composition?

Answer 13

1) Use inheritance over composition in Python to model a clear “IS A” relationship. 2) Use inheritance over composition in Python to leverage BOTH the interface and implementation of the base class. 3) Use inheritance over composition in Python to provide mixin features to several unrelated classes when there is only one implementation of that feature.

If you’re able to justify an inheritance between two classes both ways they probably should not derive from each other.

Question 14

describe isinstance( ) in python?

Answer 14

Return True if the object argument is an instance of the classinfo argument, or of a (direct, indirect or virtual) subclass thereof. If the object is not an object of the given type, the function always returns False.

Question 15

What is the __repr__( ) method in python?

Answer 15

__repr__() compute the “official” string representation of an object (a representation that has all information about the object). Used for debugging and should be wrapped in backquotes.

Question 16

When should you use composition over inheritance?

Answer 16

1) Use composition over inheritance in Python to model a has a relationship that leverages the implementation of the component class. 2) Use composition over inheritance in Python to create components that can be reused by multiple classes in your Python applications. 3) Use composition over inheritance in Python to implement groups of behaviors and policies that can be applied interchangeably to other classes to customize their behavior.

Question 17

Describe a lambda function.

Answer 17

A lambda function is used to describe an anonymous function in python. An anonymous function is a function with no name. Although syntactically they look different, lambda functions behave in the same way as regular functions that are declared using the def keyword.

Question 18

Describe characteristics of lambda functions

Answer 18

1) A lambda function can take any number of arguments, but they contain only a single expression. An expression is a piece of code executed by the lambda function, which may or may not return any value.
2) Syntactically, lambda functions are restricted to only a single expression.
3) Structure - lambda argument(s): expression
4) The lambda operator cannot have any statements and it returns a function object that we can assign to any variable.
5) useful as temporary functions for higher-order functions (functions that take other functions as arguments)

Question 19

what is a set?

Answer 19

An unordered list with no duplicates.

Question 20

Describe generator functions in python.

Answer 20

generators are functions that contain a yield keyword. The yield keyword returns a value and the function state is saved until it’s evaluated again. It causes a pause in execution.

Question 21

What is a generator?

Answer 21

Generators are a special type of iterator in python that is lazily evaluated. It’s particularly useful for iterating over large lists and sequences because the entire sequence isn’t stored in memory.

Question 22

What is a decorator?

Answer 22

Decorators add additional functionality or modify the behaviour of your functions without changing its definition.

Question 23

How do decorators work?

Answer 23

It wraps and processes your function, then returns the wrapped function.

Question 24

Describe some of the changes between Python 2 and 3.

HINT 4

Answer 24

1) print( ).
2) Unicode support natively.
3) Exception handling syntax is slightly different.
4) The division operater ( / ) performs floating-point division in python 3. the operator ( // ) floor division is what ( / ) was in python 2

Question 25

What is super( )

Answer 25

At a high level super gives you access to a parent classes attributes and methods. All methods that are called with super() need to have a call to their superclass’s version of that method.

Question 26

What is pass by reference?

Answer 26

pass-by-reference, the function, and the caller both use the exact same variable and object.

Question 27

What is pass by value?

Answer 27

pass-by-value, the function receives a copy of the argument objects passed to it by the caller, stored in a new location in memory. The copies of variables and objects in the context of the caller are completely isolated.

Question 28

Python is pass by object reference instead of pass by reference or pass by value? what does that mean?

Answer 28

Python is different. As we know, in Python, “Object references are passed by value”. A function receives a reference to (and will access) the same object in memory as used by the caller. However, it does not receive the box that the caller is storing this object in; as in pass-by-value, the function provides its own box and creates a new variable for itself. But the key is that they really are different names and different boxes.

Question 29

Describe how we create a generator expression.

Answer 29

A generator expression is similar to a list comprehension except it uses parenthesis ( ) instead of square brackets [ ]

Question 30

What are some of the ways to define a dictionary? Hint 3*

Answer 30

1) x = dict((k, v), (k1, v1)..)
2) y = dict(k=v, k1=v1, k2=v2)
3) z = {k:v, k1:v1, k2:v2}

Question 31

Describe ways to access dictionary values? ***HINTS python question, 3 ways.

Answer 31

1) dict[‘key’]
2) dict.get(‘key’, default=None)
3) dict.setdefault(‘key’, value) where key is assigned value if it doesn’t exist.

Question 32

describe different ways to set values in a dictionary. HINT 3

Answer 32

1) dict[‘key’] = value
2) from the collections module import defaultdict. defaultdict(default_value, initial_dict=None). defaultdict is similar to a dictionary except if a key is accessed before assigned a value, it binds the key to the default_value. the default_value can be a function.
3) dict.setdefault(‘key’, value) where key is assigned value if it doesn’t exist.

Question 33

Describe different ways to iterate over a dictionary in python.

Answer 33

1) for key in dict(…)
2) if key in dict(…)
3) for k, v in dict(…).items( )

Question 34

describe the Counter class from the collections module.

Answer 34

dict subclass for counting hashable objects. Elements are counted from an iterable or initialized from another mapping.

most_common( ) and elements( ) are the two most widely used methods from this class.

Question 35

Describe the deque object

Answer 35

list-like container with fast appends and pops on either end. inserts in regular lists is O(n)

Question 36

What are some useful itertools methods?

Answer 36

1) repeat(object, times=[optional]) repeats the object infinite times, simply call next( ) to retrieve the next objects.
2) permutations(iterable, length) - returns a list of permutations.
3) combinations(iterable, length)
4) cycle(iterable)

Question 37

What are some useful functool methods

Answer 37

1) reduce(func, iterable) Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value.
2) cached_property (python 3.8) Transform a method of a class into a property whose value is computed once and then cached as a normal attribute for the life of the instance.
3) lru_cache Decorator to wrap a function with a memoizing callable that saves up to the maxsize most recent calls

Question 38

What is a regular expression?

Answer 38

A regex is a special sequence of characters that defines a pattern for complex string-matching functionality.

Question 39

Describe 3 ways you can merge dictionaries in python.

Answer 39

1) using the | operator in python 3.9 >
2) using the spread operator **
3) using the built dict method update( )

Question 40

Describe a data class in python

Answer 40

A data class is a class that comes with a lot of basic functionality built in. It is declared using the @dataclass decorator from the module dataclasses. For instance, you can instantiate, print, and compare data class instances straight out of the box