Change starting index of list in python?

Question

I made a program to find a prime number and store in list. Now i want to print the exact position of the prime number For eg. in the range of 2 to 20 If i take the input 6 it should print 13 not 17.

q=[]
for num in range(1,101):
    if num>1:
        if all(num%i!=0 for i in range(2,int(num**0.5+1))):
            q.append(num)

Padraic Cunningham · Accepted Answer · 2015-08-02 19:37:48Z

2

Just deduct 1 from the index:

print(q[6-1]) # -> 13

lists are zero-based so if you are going to use one-based indexing you need to simply subtract 1, you should also maybe handle the case where a user enters 0.

You can also start your range at 3 and use a step of 2 to get your primes:

q = [2]
for num in range(3, 101, 2):
    if num > 1:
        if all(num % i != 0 for i in range(3, int(num ** 0.5 + 1), 2)):
            q.append(num)

edited Aug 2, 2015 at 19:37

answered Aug 2, 2015 at 19:18

Padraic Cunningham

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2 Comments

YaSh Chaudhary Over a year ago

so what will you suggest for zero?

Padraic Cunningham Over a year ago

@YaShChaudhary, if you truly wanted to have a one-based array then an indexerror would be appropriate but it is completely dependant on what you are trying to acheive

Michael Neylon · Accepted Answer · 2015-08-02 19:19:59Z

2

q=[]
for num in range(1,101):
    if num>1:
        if all(num%i!=0 for i in range(2,int(num**0.5+1))):
             q.append(num)
index  = 6
print q[index-1]

answered Aug 2, 2015 at 19:19

Michael Neylon

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