How to update value in dictionary?

[ssecorp]

dict.update({"a ":1}) SETS the dict item "a" 's value to 1.

i want to increase it by 1. isnt that possible in an easy way? I
should use a tuple for this?

[Iain King]

Re: How to update value in dictionary?

On Aug 27, 2:40 pm, ssecorp <circularf...@g mail.comwrote:

dict.update({"a ":1}) SETS the dict item "a" 's value to 1.
>
i want to increase it by 1. isnt that possible in an easy way? I
should use a tuple for this?

dict["a"] += 1

Iain

[Diez B. Roggisch]

Re: How to update value in dictionary?

ssecorp wrote:

dict.update({"a ":1}) SETS the dict item "a" 's value to 1.
>
i want to increase it by 1. isnt that possible in an easy way? I
should use a tuple for this?

1) Don't use dict as name for a dictionary, it shadows the type dict

2) setdefault is your friend

d = {}
d['a'] = d.setdefault('a ', 1) + 1

Diez

[bearophileHUGS@lycos.com]

Re: How to update value in dictionary?

ssecorp wrote:

dict.update({"a ":1}) SETS the dict item "a" 's value to 1.

That works but it's not the right way to do that, use this:

d["a"] = 1

Bye,
bearophile

[mblume]

Re: How to update value in dictionary?

Am Wed, 27 Aug 2008 15:45:13 +0200 schrieb Diez B. Roggisch:

>

>dict.update({" a":1}) SETS the dict item "a" 's value to 1.
>>
>i want to increase it by 1. isnt that possible in an easy way?
>I should use a tuple for this?

>
>
1) Don't use dict as name for a dictionary, it shadows the type dict
>
2) setdefault is your friend
>
d = {}
d['a'] = d.setdefault('a ', 1) + 1
>

d['a'] = d.get('a', 1) + 1

seems to me a little better, as d['a'] doesn't get set twice, right?

Curious
Martin

[Fredrik Lundh]

Re: How to update value in dictionary?

mblume wrote:

>2) setdefault is your friend
>>
>d = {}
>d['a'] = d.setdefault('a ', 1) + 1
>>

d['a'] = d.get('a', 1) + 1
>
seems to me a little better, as d['a'] doesn't get set twice, right?

setdefault is pronounced "get, and set if necessary". it only updates
the dictionary if the key isn't already there:

>>help({}.setde fault)

Help on built-in function setdefault:

setdefault(...)
D.setdefault(k[,d]) -D.get(k,d), also set D[k]=d if k not in D

(since setdefault is a method, the second argument is evaluated whether
it's used or not, but that's true for your approach as well, and isn't
much of a problem for a light-weight object like the integer 1.)

</F>

[MRAB]

Re: How to update value in dictionary?

On Aug 27, 8:01 pm, Fredrik Lundh <fred...@python ware.comwrote:

mblume wrote:

2) setdefault is your friend

>

d = {}
d['a'] = d.setdefault('a ', 1) + 1

>

d['a'] = d.get('a', 1) + 1

>

seems to me a little better, as d['a'] doesn't get set twice, right?

>
setdefault is pronounced "get, and set if necessary".  it only updates
the dictionary if the key isn't already there:
>
 >>help({}.setde fault)
Help on built-in function setdefault:
>
setdefault(...)
     D.setdefault(k[,d]) -D.get(k,d), also set D[k]=d if k not in D
>
(since setdefault is a method, the second argument is evaluated whether
it's used or not, but that's true for your approach as well, and isn't
much of a problem for a light-weight object like the integer 1.)
>

Both

d['a'] = d.setdefault('a ', 1) + 1

and

d['a'] = d.get('a', 1) + 1

will set d['a'] to 2 if 'a' isn't initially in d.