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.

• deceze: You get no output? Not even "do nothing"?
• Peter: 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.
• dedObed: It would be much better to separate the input from the function, so you would call it as func(x).
• dnsiv: Why is your range declared as 50? Shouldn't you take the size of A?
• Matthias: 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)))

Answer 1

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()

Answer 2

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")

Answer 3

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.

• Mass17: Thanks for the link @mehrdad-pedramfar

Answer 4

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()