convert this while loop to a more efficient while loop

Question

i am trying to work this out is the simplest way, i am a beginner, this is the question i have been asked and the code:

Program logic alternatives. Consider the following code, which uses a while loop and found flag to search a list of powers of 2 for the value of 2 raised to the fifth power(32) It's stored in a module file called power.py.

L = [1, 2, 4, 8, 16, 32, 64]
X = 5
found = False
i = 0

while not found and i < len(L):
    `if 2 ** X == L[i]:`
        found = True
    else:
        i = i+1

if found:
    ('at index', i)
else:
     print(X,'not found')

The question it asked me to do is a couple but the first one is confusing me,

a.)First, rewrite the code with a while loop else clause to eliminate the found flag and final if statement.

Any help is appreciated please. Thanks.

#1 Rewrite the code without a found variable. #2 Rewrite the code so the only if statement is inside the while loop (this must be done as a result of #1) ... are you allowed the use of functions? — user166390
– user166390, Commented Mar 28, 2012 at 11:05
Doesn't this question belong to codereview.stackexchange.com? — Eric O. Lebigot
– Eric O. Lebigot, Commented Mar 28, 2012 at 11:08

codetantra · Accepted Answer · 2012-03-28 11:10:43Z

1

L = [1, 2, 4, 8, 16, 32, 64] 
X = 5 
i = 0 
while i < len(L): 
    if 2 ** X == L[i]: 
        print('at index',i)
        break;
    i = i+1 
    if i==len(L): print(X,'not found')

answered Mar 28, 2012 at 11:10

codetantra

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2 Comments

thechrishaddad Over a year ago

Thanks that's exactly what i was looking for the only thing is does break count as a else clause?

codetantra Over a year ago

to incorporate the else clause of the while statement, change the last line of code as 'else: print(X,'not found')'

brice · Accepted Answer · 2012-03-28 11:07:15Z

1

Python comes with batteries

Use the index method:

L = [...]
try:
    i = L.index(2**X)
    print("idex: %d"%i)
except ValueError as err:
    print("not found")

answered Mar 28, 2012 at 11:07

brice

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1 Comment

Eric O. Lebigot Over a year ago

This is the way to do the job at hand, but this does not appear to be an answer to the question ("First, use an else while-loop clause,…")

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