facing difficulty to print out the iteration

Question

it's showing that 'nonetype object is not iterable', why? If you have solution please help me to solve out. thanks

def if_primes():
num = 2
def is_prime(num): #defined it by myself
while True:
if is_prime(num):
yield num
num += 1

for num in if_primes():
print(num)

https://sololearn.com/compiler-playground/cz3V8Wl4rLH7/?ref=app

Answer 1

I think you mean 'NoneType' object is not iterable.

If you defined a function but not specify the return value, None will be returned.

In your if_primes() function, there is no return value.
Therefore line 9 becomes:
for num in None:
Since None, a 'NoneType' object, is not iterable, you get the error message.

You can add return num in line 8 for your if_primes() function, and you will see the error message change accordingly.

Answer 2

In this case, the if_primes() function creates a generator object, and it returns 5, 4, 3, 2, 1. You can test it with the code below:
x = if_primes()
print(type(x)) # <class 'generator'>
next(x) # 5
next(x) # 4
next(x) # 3
next(x) # 2
next(x) # 1
next(x) # error, StopIteration
You can think of it similar to range(5).

Unlike return, yield not only return a value to its caller, but also keep the code running. So it does "returning" a value without a "return" keyword.

In your previous example, the yield is returning a value to itself (is_prime() function), but it doesn't have a specific return value to its caller if_primes() method. Therefore if_primes() return None to its caller: line 9.

Answer 3

thanks for your reply but what about this one...?

def if_primes():
i = 5
while i > 0:
yield i
i -= 1

for i in if_primes():
print(i)

here you write any return for the if_primes() function?