If condition inside for loop in python

Question

I am newbie to the python. I am sure this is a very basic question, but still I don’t get it in python.

I have two 1D-arrays, A and B of length 50. I want to find for a given user input, A[0], I must return B[0], A[1]——> B[1] and so forth..

I have created a function to this task.

 A = [10, 20,.... 500]
 B = [1, 4,.... 2500]

def func():
    x = input("enter a value from the array A: ") #user input
    for i in range(50):
       if A[i] == x:
          print(B[i])

       else:
          print("do nothing")

func()

But if I call the function, I get nothing. I would appreciate if someone could help me. Thanks.

The input command is different on Python 2 and 3, so I'm not 100% sure, but I have a feeling you need to convert it to an integer. You're basically doing something like if 2 == "2", which is False. — Peter
– Peter, Commented Sep 25, 2018 at 13:55
It would be much better to separate the input from the function, so you would call it as func(x). — dedObed
– dedObed, Commented Sep 25, 2018 at 13:56
Why is your range declared as 50? Shouldn't you take the size of A? — dnsiv
– dnsiv, Commented Sep 25, 2018 at 13:56
Using a dictionary would be a better way: print((dict(zip(A, B))).get(int(x), None)). In a real program you would construct the dictionary once and reuse it. If you really want the "do nothing": print('\n'.join(b if int(x) == a else 'do nothing' for (a, b) in zip(A, B))) — Matthias
– Matthias, Commented Sep 25, 2018 at 14:28

EMKAY · Accepted Answer · 2018-09-25 13:56:43Z

5

try this

  A = [10, 20,.... 500]
  B = [1, 4,.... 2500]

  def func():
     x = int(input("enter a value from the array A: ")) #user input
     for i in range(50):
       if A[i] == x:
         print(B[i])

       else:
        print("do nothing")

  func()

answered Sep 25, 2018 at 13:56

EMKAY

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Comments

Sociopath · Accepted Answer · 2018-09-25 14:01:12Z

1

Maybe you can do it like this:

def func():
   x=int(input("enter a value from the array A: "))
   if x in A:
       idx = A.index(x)
       print(B[idx])
   else:
       print("do nothing")

answered Sep 25, 2018 at 14:01

Sociopath

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Comments

Mehrdad Pedramfar · Accepted Answer · 2018-09-25 13:59:26Z

0

This is a little better, you don't need to use range() and will not print a lot of do anything it will print do nothing if the value wasn't in A try this:

A = [10, 20,.... 500]
B = [1, 4,.... 2500]

def func():
    x = int(input("enter a value from the array A: ")) #user input
    for i,v in enumerate(A):
        if v == x:
            print(B[i])
            break

    else:
        print("do nothing")

func()

read here to learn about for else.

answered Sep 25, 2018 at 13:59

Mehrdad Pedramfar

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1 Comment

Mass17 Over a year ago

Thanks for the link @mehrdad-pedramfar

Damiano Tagliaferri · Accepted Answer · 2018-09-25 14:23:23Z

0

Try this:

A = [10, 20,.... 500]
B = [1, 4,.... 2500]

def func():
    print('A = ' + str(A))
    x = int( input("Enter a value from the array A: ") )
    # enter code here

    # range(min_included, max_NOT_included) -> so range is [0, 1, 2 ... 49]
    for i in range(0, 50):
       if A[i] == x:
          print(B[i])

       else:
          pass  #equals 'do nothing', so you can even remove the 'else'

func()

answered Sep 25, 2018 at 14:23

Damiano Tagliaferri

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