类型错误：get() 不接受关键字参数

Question

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?

Answer 1

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

Answer 2

错误消息说get接受关键字参数，但您提供的参数为default=0

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

Answer 3

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)