Python Forum

coding a generator. but what if it has nothing to yield? just return? return anything in particular?

As per PEP255, empty return statement is allowed in the generator function

borrowing the example from pep255

def f1():
    try:
        return
    except:
        yield 1

print('Loop over empty generator')
for item in f1():
    print(item)
print('Loop over empty generator completed')

print('call next() on empty generator')
next(f1())

Output:
Loop over empty generator
Loop over empty generator completed
call next() on empty generator
Traceback (most recent call last):
  File "***", line **, in <module>
    next(f1())
StopIteration

or without return

def empty_generator():
    for item in []:
        yield item

print('Loop over empty generator')

for item in empty_generator():
    print(item)

print('Loop over empty generator completed')

print('call next() on empty generator')
next(empty_generator())

Output:
Loop over empty generator
Loop over empty generator completed
call next() on empty generator
Traceback (most recent call last):
  File "***", line **, in <module>
    next(empty_generator())
StopIteration

This one works too

>>> def foo():
...     if False: yield
... 
>>> list(foo())
[]
>>>