How can I get the number from iterator object. (Python2.7)

Question

A method returns iterator object. I want to check the number of data to test.

I think it is a simple question, but I coundn't resolve it.

    records = a_function()
    self.assertEqual(1, len(records)) # TypeError: object of type 'listiterator' has no len()

Python2.7

There is no question in your post. What do you mean with _number of data_? — clemens, Nov 15 '16 at 06:45

juanpa.arrivillaga · Accepted Answer · 2016-11-15T06:47:18.573

11

You need to convert the iterator to a list first:

len(list(records))

See:

>>> some_list = [1, 2, 3, 4, 5]
>>> it = iter(list)
>>> it = iter(some_list)
>>> len(it)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'list_iterator' has no len()
>>> len(list(it))
5
>>>

Note, however, that this will consume the iterator:

>>> list(it)
[]
>>>

edited Nov 15 '16 at 06:47

answered Nov 15 '16 at 06:45

juanpa.arrivillaga

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Thank you. It worked fine. Yes, `records` is iterator object, this name is not suitable, I think. Thank you everyone. – Maiko Ohkawa Nov 15 '16 at 06:55

Stormvirux · Answer 2 · 2016-11-15T07:00:39.123

2

You can easily do it by

sum(1 for _ in it)

where it is the iterator you want to find length.

edited Nov 15 '16 at 07:00

answered Nov 15 '16 at 06:51

Stormvirux

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That's a bit cheeky: dupe flagging and then posting an answer. But I'll let you get away with it this time. ;) – PM 2Ring Nov 15 '16 at 06:55
1

;). Wont repeat again – Stormvirux Nov 15 '16 at 06:56

How can I get the number from iterator object. (Python2.7)

2 Answers2