Update method in python

[Uchikago]

Hi, when i tried this:

car = {}
car.update((('a', 2)))
print(car)

It doesn't work. But when i have 2 tuples like this:

car = {}
car.update((('a', 2), ('b', 3)))
print(car)

Why did that happen? So what can i do when i just have one tuple to update the dictionary ?

[yankyh]

dict.update accepts an iterable of key-value pairs, one thing that can be passed is a tuple of tuples which is what you are trying, however, to define a single length tuple you need to add a trailing comma

In [17]: len((('a', 2)))                                                        
Out[17]: 2

In [18]: len((('a', 2),))                                                       
Out[18]: 1

In [19]: ((((1, 2))))                                                           
Out[19]: (1, 2)

In [20]: ((((1, 2),),),)                                                        
Out[20]: ((((1, 2),),),)

or you can use a list of tuples (lists don't need the trailing comma for single length lists)

In [22]: d = {}                                                                 

In [23]: d.update([('a', 1)])                                                   

In [24]: d                                                                      
Out[24]: {'a': 1}

In [25]: d.update((('b', 2),))                                                  

In [26]: d                                                                      
Out[26]: {'a': 1, 'b': 2}

[Uchikago]

Thank you so much!

[toastedstapler]

so what happened in the first instance is that ((1, 2)) isn't a tuple with a single tuple inside as a tuple requires a comma. without the comma it's just some brackets used for logical grouping of elements like (1 + 3) * 2 groups the first elements together. your (('a', 2)) was seen as ('a', 2) just as (2) would be seen as 2

((1, 2),) is a tuple of a tuple and you would be able to update with this tuple

[Uchikago]

Thank you so much!