python - TypeError: get() takes no keyword arguments

67
votes

I'm new at Python, and I'm trying to basically make a hash table that checks if a key points to a value in the table, and if not, initializes it to an empty array. The offending part of my code is the line:

converted_comments[submission.id] = converted_comments.get(submission.id, default=0)

I get the error:

TypeError: get() takes no keyword arguments

But in the documentation (and various pieces of example code), I can see that it does take a default argument:

https://docs.python.org/2/library/stdtypes.html#dict.get http://www.tutorialspoint.com/python/dictionary_get.htm

Following is the syntax for get() method:

dict.get(key, default=None)

There's nothing about this on The Stack, so I assume it's a beginner mistake?

3
python
The example in the second link is funny. - ziyuang
a bit offtopic, but you can use defaultdict from the collections module to achieve the same functionality. - moshevi
people might hate me for suggesting this but I've being doing this for range since I have a terrible memory of what the order of things are. Imo this shouldn't be a problem so I'm fixing it: range(*{'start':0,'stop':10,'step':2}.values()) - Charlie Parker

3 Answers

32
votes

The error message says that get takes no keyword arguments but you are providing one with default=0

converted_comments[submission.id] = converted_comments.get(submission.id, 0)
151
votes

Due to the way the Python C-level APIs developed, a lot of built-in functions and methods don't actually have names for their arguments. Even if the documentation calls the argument default, the function doesn't recognize the name default as referring to the optional second argument. You have to provide the argument positionally:

>>> d = {1: 2}
>>> d.get(0, default=0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: get() takes no keyword arguments
>>> d.get(0, 0)
0
2
votes

Many docs and tutorials, for instance https://www.tutorialspoint.com/python/dictionary_get.htm, erroneously specify the syntax as

dict.get(key, default = None)

instead of

dict.get(key, default)