Can any one help me understand the below code???

Question

def spam(a):
def eggs():
a=[5]
return a
def bacon():
a[0]+=1
eggs()
bacon()
return a[0]

print(spam([2]))

Output:3(how?!)

Answer 1

spam([2])

[2] is a List with only one element the number 2
The list is passed into the method spam
spam has 2 sub methods eggs and bacon that are defined
The eggs method is called
inside the eggs method a new variable a is created and has the list [5] set to it.
This variable a shadows the a variable that was passed into the method and is not the same.
a is returned from the eggs method, but is not used, so the entire eggs method has no effect.
The bacon method is called.
inside the bacon method the line:
a[0]+=1
retrieves the value of the 0 position element of the list a (2) and increments its value by 1
The list a now equals [3]
Now the return a[0] line runs retrieving the value 3 at the 0 position of the list a and returns it to the print method outputting 3.

Answer 2

Actually, it's a matter of proper understanding of variable scopes. What spam does, is it ultimately only increases its argument by 1 with its inner method bacon() (a[0]+=1)
Earlier, the eggs() method returns a equal to [5], but it is done within the local spam() method scope. When it goes down, it executes the bacon() method, which again recalls a[0] as spam() method's parameter (which you provide as [2]). So it augments it by one and then returns it.
So it gives you output 3

Answer 3

This has to do with variable scopes, this thread explains it pretty well https://stackoverflow.com/questions/291978/short-description-of-the-scoping-rules (:

As for the code above:
1) list [2] gets passed to method spam
2) sub method of spam (eggs) gets called. a=[5] doesnt assign the value [5] to the list [2] passed to spam, but rather its a declaration of variable a within the scope of the eggs method and it has nothing to do with the initial list passed to spam.The local scope a then gets returned to nothing because eggs is called but not assigned to anything
3) sub method of spam (bacon) gets called. in this case a[0]+=1 adds 1 to the value of the first item in list named a, but since there are no lists named a in the local variable scope of bacon, it looks for the next scope level and finds the variable a in its parent method spam, so it assigns the value to it.

Answer 4

Congrats for gold, Maya! 👏👏👏👏👏
https://www.sololearn.com/Discuss/454972