Patterns for clearer python

Question 1

What is an assertation?

Answer 1

At its core, Python’s assert statement is a debugging aid,that tests a condition. If the assert condition is true, nothing happens, and your program continues to execute as normal. But if the condition evaluates to false, an Assertion-error exception is raised with an optional error message.

Question 2

Why instead of assertions, we may use if-conditions>

Answer 2

Assertions are used to inform unrecoverable errors, where no corrective actions can happen.

Question 3

Whats the biggest caveat with assertion?

Answer 3

The biggest caveat with assertions is that they can be globally disabled with -o and -OO option

Question 4

Assertions provoke security holes. How to prevent this/

Answer 4

Never use it for data validation purposes.

Question 5

Name another caveat of assertions.

Answer 5

Assertions that never fail, specially when it is passed as tuple . assert (x>0,”Message”). Non empty tuples in python always are considered true.

Question 6

Why opening files with “with” statement is recommended?

Answer 6

It is recommended because it ensures that the file descriptors are closed after the exit of ‘with’

Question 7

How “with” functionality can be utilized in custom-made classes?

Answer 7

“With” functionality in custom made classes can be implemented with the use of the so call context managers.

Question 8

What is a context manager?

Answer 8

A context manager is a simple interface/protocol that the custom made classes should follow in order to support “with” functionality/ SImply the classes should contain the __enter__ and __exit__ methods.

Question 9

What does the leading underscore mean in variable nomenclature?

Answer 9

It is a convention that the variable is used only for internal use.

Question 10

When the leading underscore violated the convention.

Answer 10

It violates the convention when importing modules.
So if you use 
>>from mymodule import *
instead of a normal import
>>import mymodule

Question 11

When trailing underscore is used?

Answer 11

The trailing underscore is used when the most fitting name for a variable is taken.

Question 12

What a leading double underscore prefix means?

Answer 12

The leading double underscore provokes name mangling.

Question 13

What is name mangling?

Answer 13

The name mangling is the process that the interpret changes the name of a class attribute to avoid collisions when the class is extended to sub classes.

Question 14

How the name magling takes place?

Answer 14

Let's say we have a class Test:
class Test:
    def \_\_init\_\_(self,x,u):
        self._x=x
        self.\_\_u=u
    def return_var(self):
        print(self._x)

class SubTest(Test):
    def \_\_init\_\_(self,x,y):
        super().\_\_init\_\_(x,y)
        self.x="overiden"
        self.\_\_u='overiden'

print(test.__u) will throw an error

Question 15

How the name magling takes place?

Answer 15

For the class Test
class Test:
    def \_\_init\_\_(self,x,u):
        self._x=x
        self.\_\_u=u
    def return_var(self):
        print(self._x)

The dir(Test) lies the following:

[‘_Test__u’, ‘__class__’, ‘__delattr__’, ‘__dict__’, ‘__dir__’, ‘__doc__’, ‘__eq__’, ‘__format__’, ‘__ge__’, ‘__getattribute__’, ‘__gt__’, ‘__hash__’, ‘__init__’, ‘__init_subclass__’, ‘__le__’, ‘__lt__’, ‘__module__’, ‘__ne__’, ‘__new__’, ‘__reduce__’, ‘__reduce_ex__’, ‘__repr__’, ‘__setattr__’, ‘__sizeof__’, ‘__str__’, ‘__subclasshook__’, ‘__weakref__’, ‘_x’, ‘return_var’]

Question 16

Does the name mangling(double leading underscore) apply to methods?

Answer 16

Yes

Question 17

What is dunder?

Answer 17

Double underscores (__init__)

Question 18

How many string formatting methods exits?

Answer 18

Four

a) Old way
b) New way
c) Formatted string literals
d) Template

Question 19

Describe old way of string formatting

Answer 19

Using % operator,it’s a shortcut that lets you do simple positional formatting very easily.

‘Hello, %s’ % name

Question 20

Describe the new way of formatting

Answer 20

Using the format command
»” My name is {name}”.format(name=”Mitsos”)

With this implementation, the position of arguments is negleted

Question 21

Formatted string literals

Answer 21

f’ My name is {name}’

This method needs to initialize previously the name variable