Brilliant, thank you. I hadn't realised that Python could do lambda
expressions as well, that's a bonus.
Leo
On 01/09/12 16:10, Robin Wilson wrote:
> Hi Leo,
>
> You can do this fairly easily using the 'key' keyword argument for
> the 'sorted' function. Sorting a normal list can be done easily as:
>
> s = sorted(test)
>
> But if you want to tell it how to generate the value to sort on, you
> can use the key keyword, for example:
>
> s = sorted(test, key=str.lower)
>
> As you can see, the key parameter gives a function to be called on
> each of the elements before comparing them. In that case it uses a
> built-in Python function to convert each element to lowercase, but
> you can write your own function very easily to do what you want. You
> can do this by writing a normal function, like:
>
> def f(value): return value.prop
>
> and then calling it as follows:
>
> s = sorted(test.itervalues(), key=f)
>
> or by writing a lambda function, which is basically the same, but
> inline and without a name:
>
> s = sorted(test.itervalues(), key=lambda x: x.prop)
>
> I'm using test.itervalues() as the list to use here as that will just
> provide a list of the values in the dictionary, not the keys.
>
> Hope that helps,
>
> Cheers,
>
> Robin
>
> On 1 Sep 2012, at 15:53, Leo <linux@???> wrote:
>
>> If I have a dictionary in Python, where the keys are strings, and
>> the values are instances of a class of mine, how can I get the list
>> of keys sorted based on a property on my class? I can obviously do
>> this manually, but was wondering if there was an inbuilt Python way
>> of doing it more easily. As an example:
>>
>> Class MyClass: def __init__(self, prop) self.prop = prop
>>
>> def main(): test=dict() test["a"] = MyClass(46) test["b"] =
>> MyClass(3) test["c"] = MyClass(15)
>>
>> # I would like to generate sortedTest=list() #containing b, c, a in
>> that order.
>>
>> Thanks, Leo
>>
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