Computer Science Canada

A Python One-Line Challenge
Author:  wtd [ Fri Jul 29, 2005 4:44 am ]
Post subject:  A Python One-Line Challenge
Sets are an unordered collection of data. They have the useful property that they only contain any given value once.

code:
>>> set([1,2,3,2,1,4])
set([1, 2, 3, 4])


We can do fancy manipulations with sets. We can "and" two sets, and get back only the elements contained in both sets.

code:
>>> set([1,2]) & set([2,3])
set([2])


We can "or" sets and get any elements in either set.

code:
>>> set([1,2]) | set([2,3])
set([1, 2, 3])


And, we can "xor" (exclusive or) two sets. This gives us only elements which are not shared by the two sets.

code:
>>> set([1,2]) ^ set([2,3])
set([1, 3])


Now, given a list of sets called "foo":

code:
foo = [set([1,2,3]), set([4,5,6]), set([3,7,9,1])]


Write a single line of code which generates a new set containing all of the elements in all of the sets in "foo".

No semi-colons are allowed, and the code should be readable.

Lambda functions are allowed.

Questions on how sets work are quite welcome. Smile
Author:  lyam_kaskade [ Fri Jul 29, 2005 4:56 am ]
Post subject: 
ah! I did it! Very Happy

code:

>>foo = [set([1,2,3]), set([4,5,6]), set([3,7,9,1])]


code:

>>foo [0] | foo[1] | foo[3]
set ([1, 2, 3, 4, 5, 6, 7, 9])


Unless I misunderstood the question Eh
What's a lambda function?
Author:  MysticVegeta [ Fri Jul 29, 2005 7:42 am ]
Post subject: 
Isnt "lambda" a greek alphabet, i think it comes after "kappa". lol i was bored so i memorized all of them last year in grade 8
Author:  wtd [ Fri Jul 29, 2005 1:17 pm ]
Post subject: 
lyam_kaskade wrote:
ah! I did it! Very Happy

code:

>>foo = [set([1,2,3]), set([4,5,6]), set([3,7,9,1])]


code:

>>foo [0] | foo[1] | foo[3]
set ([1, 2, 3, 4, 5, 6, 7, 9])


Unless I misunderstood the question Eh


A little bit. I may not have been clear enough, though.

The one line of code has to work for any number of sets in "foo".

lyam_kaskade wrote:
What's a lambda function?


It's a small nameless function. A very simple example:

Python:
lambda a, b: a + b
Author:  rizzix [ Fri Jul 29, 2005 1:27 pm ]
Post subject: 
woah, lol. what just happened.. forum was messed up for a second here..
Author:  wtd [ Tue Aug 23, 2005 4:52 pm ]
Post subject: 
The answer, finally. Smile

code:
$ python
Python 2.4.1 (#2, Mar 30 2005, 21:51:10)
[GCC 3.3.5 (Debian 1:3.3.5-8ubuntu2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> foo = [set([1,2,3]), set([4,5,6]), set([3,7,9,1])]
>>> reduce(lambda a, b: a | b, foo, set())
set([1, 2, 3, 4, 5, 6, 7, 9])
>>> reduce(set.__or__, foo, set())
set([1, 2, 3, 4, 5, 6, 7, 9])
>>>
Author:  wtd [ Mon Sep 05, 2005 8:31 pm ]
Post subject: 
Python programmers, heed this summons!

I challenge you to take an input file like:

code:
hello=42
world=12
foo=bar
wooble=ninja


And generate a dictionary like:

Python:
{'hello': 42, 'world': 12, 'foo': 'bar', 'wooble': 'ninja'}


Assigned to a variable called fileInfo, in one line of code. Smile

Oh, and no semi-colons. No square brackets either. In an ideal solution you should use only two sets of parentheses, and no curly braces.

Be wary. The keys in a line of the file may contain more than one equals sign.
Author:  Hikaru79 [ Tue Sep 06, 2005 6:24 am ]
Post subject: 
Python:
fileInfo = dict([(x.split('=')[0],x.split('=')[1].strip()) for x in file('info.txt')])

?
Author:  wtd [ Tue Sep 06, 2005 10:55 am ]
Post subject: 
Close.

Python:
fileInfo = dict(line.split('=', 1) for line in file('info.txt'))


Ok, so three sets of parentheses. Smile
Author:  wtd [ Tue Sep 06, 2005 1:59 pm ]
Post subject: 
Now... alter the code so it properly handles the case where the key can contain more than one equals sign. Smile

A line such as:

code:
hello=world=foo=bar


Would become:

Python:
{'hello=world=foo': 'bar'}

:


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