Oct18_round

Question 1

difference between set update and set union

Answer 1

update changes the set it is called on, i.e. s.update(s1) will change s by adding s1 to it. whereas union will create a new object containing both s and s1 without modifying either.

Question 2

what are the 3 types of comprehension in python

Answer 2

list, dict and set

Question 3

The default argument in a python function is evaluated once. Give an example.

Answer 3

def f(a, L=[]):
     L.append(a)
     return L
f(1) L = [1]
f(2) L = [1,2]
etc

Question 4

if you have a list of argument L but the function f needs them unpacked, i.e. as induvidual elements, what is the syntax?

Answer 4

f(*L)

Question 5

if you have a dictionary of arguments and a function needs them induvidually, what is the syntx

Answer 5

function(**dictionar_args)

Question 6

what function shows all the attributes of an object (or all the names in the object’s namespace)

Answer 6

dir(object)

Question 7

what is the difference between the global and nonlocal keyword when used before a variable name

Answer 7

global means “place this variable in the global scope and if it’s already there, use it.”
nonlocal means “place this variable in the nearest enclosing scope and if it’s not there flag an error”

Question 8

if python finds “none” against the name of a module in sys.path, what does it do? When it does not find the path itself what does it do?

Answer 8

if it is mapped to none - modulenotfound exception is raised. Otherwise it cointinues searching.

Question 9

what is the command to upload a python package to pypi so everone can use it?

Answer 9

python setup.py reigster sdist upload

Question 10

what is the name and type of special variable that you define in __init__.py which specifies which modules are loaded into the namespace when the enclosing package is created.

Answer 10

__all__ and type is list

Question 11

how do you create a tuple with a single element

Answer 11

tup = (“singleton”,) #the races are optional

Question 12

what is the onlynamespace that remains from beginning to end in a python script?

Answer 12

The namespace containing the built in names. This is loaded when the python interpreter starts up.

Question 13

what is the lifetime of a function namespace?

Answer 13

created when a function starts and destroyed when the function exits

Question 14

when is the global namespace created?

Answer 14

when the module is read in

Question 15

what are the different types of expressions?

Answer 15

list, set and dict

Question 16

set and dict comprehensions both use curly bracer; what’s the difference in syntax?

Answer 16

set = {x for x innumbers}
dict = {x:x for x in numbers}

Question 17

what kind of a comprehension is this?

x for x in numbers

Answer 17

none, this creates a generator object

Question 18

what;s wrong with this

next(agenfunction), where agenfunction is a generator function? and how to solve the problem?

Answer 18

you need to use the return value from the generator function, i.e.
a = mygenfunction()
next(a)

Question 19

what is the difference between a single and double underscore?

Answer 19

single underscore  = attribute should be used by a class object, e.g. classname()._variable
double = variable shold only be used internal to the class and not by the clas object or any instance object of the class.