Object of type 'map' has no len() in Python 3

python python-3.x variable-length
Sonius picture Sonius · May 2, 2016 · Viewed 65.3k times · Source

I have a problem with Python 3. I got Python 2.7 code and at the moment I am trying to update it. I get the error:

TypeError: object of type 'map' has no len()

at this part:

str(len(seed_candidates))

Before I initialized it like this:

seed_candidates = map(modify_word, wordlist)

So, can someone explain me what I have to do?

(EDIT: Previously this code example was wrong because it used set instead of map. It has been updated now.)

Answer

TerryA picture TerryA · May 2, 2016

In Python 3, map returns a map object not a list:

>>> L = map(str, range(10))
>>> print(L)
<map object at 0x101bda358>
>>> print(len(L))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'map' has no len()

You can convert it into a list then get the length from there:

>>> print(len(list(L)))
10

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