CODEWITHSUNDEEP
pythonloops
MathGeek
MathGeek

Reputation: 151

Converting while loops into for loops

Convert the following while loop into a for loop. Your code should be written so that the return statement does not need to be altered. You are allowed to change the code before the while loop proper. string_list is a list of string that contains at least 15 instances of the string '***'

j=0 
while i<15: 
  if string_list[j] ='***': 
    i +=1 
  j +=1 
return j

I tried doing this first it says while i<15 and i = i+1 so i know i ranges from (0...15) not including 15 so basically we will have like i = range(15) so we will have something like:

for i in range(15):

I don't know what that j is doing there.

Upvotes: 1

Views: 16876

Answers (2)

wim
wim

Reputation: 362557

I will assume you meant to write string_list[j] == '***' instead of string_list[j] ='***'. I will also assume i is initialised to 0. 

i, j = 0, 0 
while i < 15: 
  if string_list[j] == '***': 
    i += 1 
  j += 1 
return j

The first step is to understand what the loop is actually doing. It is iterating through string_list elements, and every time an '***' is encountered, i is incremented. The loop will terminate when i reaches 15, and since a precondition was given that string_list contains at least 15 copies of '***' we do expect the loop should terminate.

When the loop terminates, i will be equal to 15 and j will simply have counted the number of elements in the list up until this point.

So to start you off, you could try iterating like this:

for s in string_list:
  if s == `***`:
    # keep track of how many times this has happened
    # break if you've seen it happen 15 times
  j += 1
return j

Upvotes: 4

John La Rooy
John La Rooy

Reputation: 304137

j = [i for i,x in enumerate(string_list) if x=='***'][15]
return j

lazy version inspired by comments from Peter and astynax

from itertools import islice
j = next(islice((i for i,x in enumerate(string_list) if x=='***'), 15, None))
return j

Upvotes: 2

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