Python - Simple input program is hanging at input statement

Question

I'm writing a simple program that takes 5 numbers, puts them in a list, divides each number by 2 and prints the output list.

list1 = input("Type 5 numbers: ").split()
for eachElement in list1:
    list1.append(str(int(eachElement)//2))
print("final numbers are "," ".join(list1[5:]))

PROBLEM: The program hangs after the first input line. In the terminal, it takes the 5 numbers but never goes onto the next line.

Type 5 numbers: 56 67 84 45 78

What can be the problem? I have used input with split in many other programs, but it hangs sometimes and works most of the time.

Answer 1

You're iterating over your list and appending to it at the same time, meaning your list grows into infinity.

Observe what happens when you print something inside the loop body:

list1 = input("Type 5 numbers: ").split()
for eachElement in list1:
    val = str(int(eachElement)//2)
    print("Appending", val)
    list1.append(val)
print("final numbers are "," ".join(list1[5:]))

This prints:

Type 5 numbers: 1 2 3 4 5
Appending 0
Appending 1
Appending 1
Appending 2
Appending 2
Appending 0
Appending 0
Appending 0
...

---

You can fix this by putting the new numbers in a different list, first:

list1 = input("Type 5 numbers: ").split()
list2 = []
for eachElement in list1:
    val = str(int(eachElement)//2)
    print("Appending", val)
    list2.append(val)
list1.extend(list2)
print("final numbers are "," ".join(list1[5:]))