dicts & lists together

[Brad Tilley]

I have a dict that associates strings to numbers like this {'abc': 1,
'xyz':2, '123':3,...} I am then given a list of strings ['abc', 'xyz',
'123',...] and asked to associate a number to each string in the list
according to the string's value in the dict. I am at a loss as to how to
do this, can someone show me where to start?

[Larry Bates]

Re: dicts & lists together

Brad Tilley wrote:[color=blue]
> I have a dict that associates strings to numbers like this {'abc': 1,
> 'xyz':2, '123':3,...} I am then given a list of strings ['abc', 'xyz',
> '123',...] and asked to associate a number to each string in the list
> according to the string's value in the dict. I am at a loss as to how to
> do this, can someone show me where to start?[/color]
[color=blue][color=green][color=darkred]
>>> xdict={'abc': 1, 'xyz':2, '123':3}
>>> xlist=['abc', 'xyz', '123']
>>> tlist=[xdict.get(v, None) for v in xlist]
>>> print tlist[/color][/color][/color]
[1, 2, 3]

Larry Bates
Syscon, Inc.

[Brad Tilley]

Re: dicts & lists together

Larry Bates wrote:[color=blue]
> Brad Tilley wrote:
>[color=green]
>> I have a dict that associates strings to numbers like this {'abc': 1,
>> 'xyz':2, '123':3,...} I am then given a list of strings ['abc', 'xyz',
>> '123',...] and asked to associate a number to each string in the list
>> according to the string's value in the dict. I am at a loss as to how
>> to do this, can someone show me where to start?[/color]
>
>[color=green][color=darkred]
> >>> xdict={'abc': 1, 'xyz':2, '123':3}
> >>> xlist=['abc', 'xyz', '123']
> >>> tlist=[xdict.get(v, None) for v in xlist]
> >>> print tlist[/color][/color]
> [1, 2, 3]
>
> Larry Bates
> Syscon, Inc.[/color]

Thank you Larry, I don't understand it, but it works ;)

[Bengt Richter]

Re: dicts & lists together

On Tue, 02 Nov 2004 13:45:38 -0500, Brad Tilley <bradtilley@gma il.com> wrote:
[color=blue]
>I have a dict that associates strings to numbers like this {'abc': 1,
>'xyz':2, '123':3,...} I am then given a list of strings ['abc', 'xyz',
>'123',...] and asked to associate a number to each string in the list
>according to the string's value in the dict. I am at a loss as to how to
>do this, can someone show me where to start?[/color]

Associate as in list of number,string pairs?
[color=blue][color=green][color=darkred]
>>> dct = {'abc':1, 'xyz':2, '123':3}
>>> strings = ['abc','xyz','12 3','error']
>>> [(dct[s],s) for s in strings][/color][/color][/color]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
KeyError: 'error'[color=blue][color=green][color=darkred]
>>> [(dct.get(s, 99999),s) for s in strings][/color][/color][/color]
[(1, 'abc'), (2, 'xyz'), (3, '123'), (99999, 'error')]

Regards,
Bengt Richter

[Pierre Barbier de Reuille]

Re: dicts &amp; lists together

Brad Tilley a écrit :[color=blue]
> Larry Bates wrote:
>[color=green]
>> Brad Tilley wrote:
>>[color=darkred]
>>> I have a dict that associates strings to numbers like this {'abc': 1,
>>> 'xyz':2, '123':3,...} I am then given a list of strings ['abc',
>>> 'xyz', '123',...] and asked to associate a number to each string in
>>> the list according to the string's value in the dict. I am at a loss
>>> as to how to do this, can someone show me where to start?[/color]
>>
>>
>>[color=darkred]
>> >>> xdict={'abc': 1, 'xyz':2, '123':3}
>> >>> xlist=['abc', 'xyz', '123']
>> >>> tlist=[xdict.get(v, None) for v in xlist]
>> >>> print tlist[/color]
>> [1, 2, 3]
>>
>> Larry Bates
>> Syscon, Inc.[/color]
>
>
> Thank you Larry, I don't understand it, but it works ;)[/color]

If you don't understand what Larry's solution does, you probably should
have a look there :

http://www.python.org/doc/2.3.4/tut/node7.html#SECTION007140000000000000000

or look in the web for "list comprehensions" in Python.

Pierre

[Raymond Hettinger]

Re: dicts &amp; lists together

"Brad Tilley" <bradtilley@gma il.com>[color=blue]
> I have a dict that associates strings to numbers like this {'abc': 1,
> 'xyz':2, '123':3,...} I am then given a list of strings ['abc', 'xyz',
> '123',...] and asked to associate a number to each string in the list
> according to the string's value in the dict. I am at a loss as to how to
> do this, can someone show me where to start?[/color]

Is this a homework assignment?


Raymond Hettinger