empty generator

[Skaperen]

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

[buran]

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

[Gribouillis]

This one works too

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