Python using a loop to search for N number and return index

问题

I have been programming for a total of three weeks. I am stuck on this problem right now:

We will pass you 2 inputs:

A list of numbers

A number, N, to look for

Your job is to loop through the list and find the number specified in the second input. Output the list element index where you find the number.

If N is not found in the list, output -1.

This is what I have so far:

import and N were provided

import sys
N= int(sys.argv[2])

this is also provided

numbers= []
for i in sys.argv[1].split(","):
    if(i.isdigit()):
        numbers.append(int(i))

mycode

for i in numbers: 
    if N in numbers: 
        print(i)
    elif N not in numbers: 
        print(-1)

This outputs the following for the random number inputs:

Program Failed for Input: 1,3,11,42,12 2 Expected Output: -1 Your Program Output: -1 -1 -1 -1 -1

This is not working and returns -1 for every number N that is not in the list numbers. I have tried using a break statement before and after print, but that stops it from printing at all. Any suggestions?

回答1:

Thank you for your comments and answers. After messing around with it a bit, this is what ended up providing the proper output:

My Code:

if N in numbers: 
    print (numbers.index(N))
if N not in numbers: 
    print(-1) 

Output:

Program Output

Input: 1,3,11,42,12 42 Your Output: 3 Challenge Feedback

Well done!

回答2:

import sys
N= int(sys.argv[2])


print "\n"

numbers= []
for i in sys.argv[1].split(","):
    if(i.isdigit()):
        numbers.append(int(i))
        print i 


i = 0


for num in numbers:

    if num == N:
        print "number found at index %d " % (i)

    i+=1

run this with python program_name.py [,x,y,z,l,m,n,] N where x,y,z,l,m,n are the numbers in the list and N is the number you search ( note the [, and ,] )

回答3:

if N in numbers :
  for num in range(len(numbers)) :
    if numbers[num] == N :
      print(num)
else :
  print(-1)

来源：https://stackoverflow.com/questions/47381225/python-using-a-loop-to-search-for-n-number-and-return-index