Computer Science Canada

Test Your Skills: Python Thread
Author:  wtd [ Thu Sep 29, 2005 2:54 pm ]
Post subject:  Test Your Skills: Python Thread
Challenge #1: Join

Lists and other iterable objects are very important in Python. It's often also important for us to be able to output a nicely formatted representation of these important objects.

The join function represents one important means of doing this.

code:
>>> ', '.join(['1', '2', '3'])
'1, 2, 3'


Reimplement it

Now, the challenge is to reimplement this function.

The Reward

50 bits, and my admiration. Admiration only if the bits system is borked.

The rules


  • The function must accept two arguments: 'lst', the list to join; and 'sep', the separator to place between the items.
  • Separators may be more than one character.
  • The function may not use the keywords 'return' or 'if', or any semi-colons. Semi-colons are permitted as the separator string passed to the function as an argument.
  • The function may not modify any arguments passed to it.
  • The function may not exceed one line of code.


Bonus

50 additional bits or simply added admiration if you can improve upon the standard library's "join" and make it work with lists containing elements that are not strings.
Author:  wtd [ Sat Nov 26, 2005 6:20 pm ]
Post subject: 
Given the snippet of code from the interactive interpreter:

code:
>>> foo()
bar
>>>


Write the code which makes this possible. Your code may not include any kind of input/output operation.
Author:  wtd [ Mon Nov 28, 2005 11:22 am ]
Post subject: 
wtd wrote:
Given the snippet of code from the interactive interpreter:

code:
>>> foo()
bar
>>>


Write the code which makes this possible. Your code may not include any kind of input/output operation.


The solution, since no one has expressed interest, is:

Python:
class foo(object):
   def __repr__(self):
      return "bar"
Author:  [Gandalf] [ Mon Nov 28, 2005 4:40 pm ]
Post subject: 
I have not looked into Python too much, so forgive any mistakes, but...
Python:
   def foo():
      return "bar"

Could you not just do that?
Author:  wtd [ Mon Nov 28, 2005 5:48 pm ]
Post subject: 
[Gandalf] wrote:
I have not looked into Python too much, so forgive any mistakes, but...
Python:
   def foo():
      return "bar"

Could you not just do that?


In that case, what'd you'd see would be:

code:
>>> foo()
"bar"
>>>
Author:  Hikaru79 [ Tue Nov 29, 2005 8:15 pm ]
Post subject: 
Okay, my turn to give one Smile This is my first try at this, so be gentle. I'll come up with more soon Smile Here it is.

Add one line of code so that the following line executes properly (and gives the result that one would intuitively assume).
Python:
Dict(foo=5, bar=12, foobar=9)


I hope this isn't too easy, hard, pointless, etc Embarassed
Author:  wtd [ Tue Nov 29, 2005 8:43 pm ]
Post subject: 
Python:
for line in file("foo.txt"): print line


Add one line of code to this such that it prints "Whoops! Empty file." if there's nothing in the file.
Author:  bugzpodder [ Thu Sep 07, 2006 12:20 pm ]
Post subject: 
if os.path.getsize("foo.txt") = 0 : print "empty file"
Author:  wtd [ Thu Sep 07, 2006 12:46 pm ]
Post subject: 
Not what I was looking for. Smile

What I am looking for is part of the loop.
Author:  bugzpodder [ Fri Sep 08, 2006 3:29 pm ]
Post subject: 
hint
Author:  wtd [ Fri Sep 08, 2006 10:43 pm ]
Post subject: 
See the Tutorial under the Documentation section on python.org. It has the answer.
Author:  Roman [ Sat Aug 09, 2008 1:09 am ]
Post subject:  Re: Test Your Skills: Python Thread
wtd @ Thu Sep 29, 2005 2:54 pm wrote:
Challenge #1: Join


code:
>>> ', '.join(['1', '2', '3'])
'1, 2, 3'




I'm very new at this, but couldn't you just do

code:

def joinFctn(sep, lst):
    print sep.join(lst)


P.S. Only three years late x_x
Author:  [Gandalf] [ Thu Oct 02, 2008 8:00 am ]
Post subject:  Re: Test Your Skills: Python Thread
Roman, you couldn't do that because you're just using the join function and printing the result. The point is the re-implement it completely.

Here's my try:
Python:
def join(lst, sep):
    return reduce(lambda x, y: x + sep + y, lst)


What I don't understand is, if we're not supposed to return anything or modifying any arguments, then what is the function supposed to do? Of course, there's probably some 'trick' that I'm missing completely. Wink

!!!
Author:  Zeroth [ Thu Oct 02, 2008 9:05 am ]
Post subject:  Re: Test Your Skills: Python Thread
Your mixing up the challenges Gandalf. One of the challenges, you cannot return anything. The other you can.
Author:  SS_198 [ Sun Feb 22, 2009 2:32 pm ]
Post subject:  Re: Test Your Skills: Python Thread
Here a way to make your python program write something without typing return : or print


python : 3.0

def helloWorld():
print ("helloWorld") # this line does not print helloworld

helloWorld() # This line print hello world


# you can type helloWorld() as many times as you like, and will print > HelloWorld <
Author:  zuzelvp [ Sat May 22, 2010 10:39 am ]
Post subject:  Re: Test Your Skills: Python Thread
[quote="[Gandalf] @ Thu Oct 02, 2008 8:00 am"]Roman, you couldn't do that because you're just using the join function and printing the result. The point is the re-implement it completely.

Here's my try:
Python:
def join(lst, sep):
    return reduce(lambda x, y: x + sep + y, lst)


What I don't understand is, if we're not supposed to return anything or modifying any arguments, then what is the function supposed to do? Of course, there's probably some 'trick' that I'm missing completely. Wink

!!![/quote]

join = lambda lst, sep: reduce(lambda x, y: x + sep + y, lst, '').replace(sep, '', 1)
Author:  zuzelvp [ Sat May 22, 2010 10:49 am ]
Post subject: 
Hikaru79 @ Tue Nov 29, 2005 8:15 pm wrote:
Okay, my turn to give one Smile This is my first try at this, so be gentle. I'll come up with more soon Smile Here it is.

Add one line of code so that the following line executes properly (and gives the result that one would intuitively assume).
Python:
Dict(foo=5, bar=12, foobar=9)


I hope this isn't too easy, hard, pointless, etc Embarassed


Anyone coming from languages like C# will need to learn this one Wink
Author:  DtY [ Sat May 22, 2010 2:15 pm ]
Post subject: 
Hikaru79 @ Tue Nov 29, 2005 8:15 pm wrote:
Okay, my turn to give one Smile This is my first try at this, so be gentle. I'll come up with more soon Smile Here it is.

Add one line of code so that the following line executes properly (and gives the result that one would intuitively assume).
Python:
Dict(foo=5, bar=12, foobar=9)


I hope this isn't too easy, hard, pointless, etc Embarassed
What do you mean "properly", I assume returns the dictionary that contains those?

Python:
Dict = dict
# Or
def Dict(**params): return params


Here's another, if anyone's interested;

In one line, write a function that will transpose a two dimensional list, that is, if the input were to look like this as a grid:
code:
A B C
D E F
G H I

The output looks like this:
code:
A D G
B E H
C F I
.
Some languages have a function that will do this, python doesn't, without using some syntax that may appear odd.
I'm pretty sure I learned how to do this from here, so at least one person should know right away.
Author:  cavetroll [ Sat May 22, 2010 10:37 pm ]
Post subject: 
DtY @ Sat May 22, 2010 2:15 pm wrote:
Hikaru79 @ Tue Nov 29, 2005 8:15 pm wrote:
Okay, my turn to give one Smile This is my first try at this, so be gentle. I'll come up with more soon Smile Here it is.

Add one line of code so that the following line executes properly (and gives the result that one would intuitively assume).
Python:
Dict(foo=5, bar=12, foobar=9)


I hope this isn't too easy, hard, pointless, etc Embarassed
What do you mean "properly", I assume returns the dictionary that contains those?

Python:
Dict = dict
# Or
def Dict(**params): return params


Here's another, if anyone's interested;

In one line, write a function that will transpose a two dimensional list, that is, if the input were to look like this as a grid:
code:
A B C
D E F
G H I

The output looks like this:
code:
A D G
B E H
C F I
.
Some languages have a function that will do this, python doesn't, without using some syntax that may appear odd.
I'm pretty sure I learned how to do this from here, so at least one person should know right away.


I think for the transposing of a list, you can just do
Python:

zip(*lst)


Where lst is your initial two dimensional list. Although it will actually return a tuple of tuples, I assume that's what you were looking for?
Author:  tedying [ Fri Jan 20, 2012 11:43 pm ]
Post subject: 
Hikaru79 @ Tue Nov 29, 2005 8:15 pm wrote:
Okay, my turn to give one Smile This is my first try at this, so be gentle. I'll come up with more soon Smile Here it is.

Add one line of code so that the following line executes properly (and gives the result that one would intuitively assume).
Python:
Dict(foo=5, bar=12, foobar=9)


I hope this isn't too easy, hard, pointless, etc Embarassed


def Dict(**x):
??return x
Author:  tedying [ Fri Jan 20, 2012 11:45 pm ]
Post subject: 
DtY @ Sat May 22, 2010 2:15 pm wrote:
Hikaru79 @ Tue Nov 29, 2005 8:15 pm wrote:
Okay, my turn to give one Smile This is my first try at this, so be gentle. I'll come up with more soon Smile Here it is.

Add one line of code so that the following line executes properly (and gives the result that one would intuitively assume).
Python:
Dict(foo=5, bar=12, foobar=9)


I hope this isn't too easy, hard, pointless, etc Embarassed
What do you mean "properly", I assume returns the dictionary that contains those?

Python:
Dict = dict
# Or
def Dict(**params): return params


Here's another, if anyone's interested;

In one line, write a function that will transpose a two dimensional list, that is, if the input were to look like this as a grid:
code:
A B C
D E F
G H I

The output looks like this:
code:
A D G
B E H
C F I
.
Some languages have a function that will do this, python doesn't, without using some syntax that may appear odd.
I'm pretty sure I learned how to do this from here, so at least one person should know right away.


My python definitely has this function:

>>> a=((1,2,3),(4,5,6),(7,8,9))
>>> zip(*a)
[(1, 4, 7), (2, 5, 8), (3, 6, 9)]
Author:  tedying [ Fri Jan 20, 2012 11:49 pm ]
Post subject: 
wtd @ Tue Nov 29, 2005 8:43 pm wrote:
Python:
for line in file("foo.txt"): print line


Add one line of code to this such that it prints "Whoops! Empty file." if there's nothing in the file.



for line in open("/dev/null"):
  print(line)
else:
  print("null")

:


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