Explanation of code

Question

I came through a quiz question in Python which I am unable to understand.Anybody please explain it:)
s=["red","green","blue","white"]
p=[1,2,3,4]
r=""
for i in range(len (s)):
r+=s[i][p[i]]
print(r)

Answer 1

Try to read parentheses from inside out!

i-Loop begins with 0; so what's p[i]? Answer's p[0]. And what's that? Looking at list p...

Ah, 1!

So the confusing line now reads [0][1], which is a lot easier. And what is that? Well, list s, element 0, and within that element the position 1...

Ah, 'e'!

And then you do that for the whole loop. Again, always from inside out!

Answer 2

s[i] is the i-th element of the list s. Same for p[i]. Now for any string, say, "Sololearn", "Sololearn"[k] is the k-th character of the string. Thus,

s[0][p[0]]="red"[p[0]]="red"[1]="e"

Similarly, s[1][p[1]], s[2][p[2]], and s[3][p[3]] are also "e". Thus the for loop is concatenating "e" with r four times. Since r was initially an empty string, the final result is "eeee".

Does that make sense?

Answer 3

The output: "eeee"
for i in range(4):
r+=s[i][p[i]]
First : r+=s[1][p[1]] == r+=red[1] == r+="e"
Second : r+=s[2][p[2]] == r+=green[2] == r+="e"
Third : r+=s[3][p[3]] == r+=blue[3] == r+="e"
Forth : r+=s[4][p[4]] == r+=white[4] == r+="e"
Then r="eeee"

Answer 4

for i in range(len(s)):
len(s)=4 means 0=>i<4
when i=0 then p[i]=1
and then s[i][p[i]] means
s[0][1]=e ,because p[i]=1
r=r+s[i][p[i]]= e because r='' and
s[i][p[i]] so r=e

when i=1
then p[i]=2
and s[i][p[i]] means s[1][2] because p[i]=2 so s[1][2]=e
and then r=r+s[i][p[i]]
r=e and s[i][p[i]]=e
so r=ee

and then so on.....