Way for see if dict has a key

[Bruno Desthuilliers]

Michele Petrazzo wrote:

Bruno Desthuilliers wrote:

but what the better


Depends on the context.


If know only one context: see if the key are into the dict... What
other
context do you know?


Why do you want to do that ?

if key in dict:
value = dict[key]
else:
value = None

could be write:

value = dict.get(key, None)

value = dict.get(key)

Yes - but :
1/ not everybody knows that dict.get() takes a second optional param.
Note that, while it happens that the default return value of dict.get()
is the same as in the above example, but it may not have been the case.

2/ Since dict.get() implicitely returns None while getattr() defaults to
raising an AttributeError unless you provide a default, I prefer to be
very explicit when using dict.get().

 

[Alex Martelli]

new syntax (2.3 and later).

Fine with Python 2.2 as well, actually -- so, "new" only in an
_extremely_ loose sense of the word.


Alex

 

[Eric Deveaud]

Seems that if "key in dict" do a simple linear search, it depends on the
number of keys in dict (and the position of the searched key etc...).

And if I'm missing the point and you it and you know why, it would be
simple to explain than to answer my question with another question.

maybee we can imagine that key in dict
just perform
try:
dict[key]
return True
except KeyError:
return False

If I understand correctly, it will be time constant no ??
just the needed time to compute the hash for the key

Eric

 

[Fredrik Lundh]

Seems that if "key in dict" do a simple linear search

that would be rather silly.

hint: http://pyref.infogami.com/__contains__

</F>

 

[Bruno Desthuilliers]

that would be rather silly.

hint: http://pyref.infogami.com/__contains__

Of course. It's just me being silly...




Thanks F

 

[Georg Brandl]

Yes - but :
1/ not everybody knows that dict.get() takes a second optional param.
Note that, while it happens that the default return value of dict.get()
is the same as in the above example, but it may not have been the case.

2/ Since dict.get() implicitely returns None while getattr() defaults to
raising an AttributeError unless you provide a default, I prefer to be
very explicit when using dict.get().

You're right, and I would write that with explicit None too.
Just wanted to continue the shortening

Georg