CODEWITHSUNDEEP
pythongenerator
gzc
gzc

Reputation: 8639

weird TypeError: 'NoneType' object is not iterable

I encounter a weird error. As these codes, both foo() and bar() return None, but it raises TypeError only when iterating bar()

def foo():
  if True:
    return

  yield 1, 2

def bar():
  return

for a, b in foo():
  print a + b

for a, b in bar():
  print a + b

Upvotes: 2

Views: 2360

Answers (5)

user3431635
user3431635

Reputation: 390

If your function does not include yield statement and you want it to return "empty iterator" you should write

def empty()
    raise StopIteration

for each in empty():
    print('this will never show up')

Upvotes: 2

JordyRitzen
JordyRitzen

Reputation: 702

The yield 1, 2 makes the difference. foo returns:

<generator object foo at 0x7f9e01a91d70>

bar returns:

None

If you'd comment the yield part the code would crash on foo() too.

You should return two values for each of the methods to solve it.

Upvotes: 1

M.T
M.T

Reputation: 5231

In your functions foo and bar, they both reach an empty return statement. They implicitly return None. foo will nonetheless generate an iterator as it includes a yield statement.

Therefore as you are looping over the output of the functions, foo will use the iterator values, while bar will not, resulting in a TypeError.

Upvotes: 0

user5547025
user5547025

Reputation:

If you

print foo()
print bar()

you get

<generator object foo at 0x7f8a79fd5eb0>
None

Upvotes: 1

Daniel Roseman
Daniel Roseman

Reputation: 600041

Because foo includes a yield statement, it is a generator, so the result from the return is always a generator object even if the actual yield statement can't be reached. A generator is true in a boolean sense, hence your result.

Upvotes: 5

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