[PLUG] Beginning Python Question #7

[Holger Stephan]

Rich Shepard wrote:
>   I found a function that accepts input of a list of items (s) and an 
> integer
> (k), and produces another list of all combinations of s things taken k at a
> time. The initial code is this:
> 
> def klistcombs(s, k):
>     """Returns list of combinations of S taken K at a time.
> 
>     S must be a list.
>     K must be >= 0.
>     If K > len(S), an empty list is returned.
>     Else if K is 0, a singleton list containing an empty list
>     is returned.
>     The k-combinations are returned in lexicographic order
>     of their indices.
> """
>     output = open('components.out', 'w')
>     input = open('components.in', 'r')
>     s = input.read()
> 
>   I added the file statements because I want to use a text file on disk as
> the source of the input list. However, it's not working.
> 
>   When I run interactively, I get an illegal syntax error at the final 'n'
> when I specify:
> 
>>>> klistcombs(components.in, 2)
> 
>   File "<stdin>", line 1
>     klistcombs(components.in, 2)
>                            ^
> SyntaxError: invalid syntax
> 
>   If I change the name of the file so there is no extension, the error
> changes to:
> 
>>>> klistcombs(components, 2)
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> NameError: name 'components' is not defined
> 
>   Since I cannot get past invoking the function, I assume the error is 
> in the
> way the function is defined. How can I define klistcombs() so that it will
> look for the input list externally, on the hard drive?
> 
> Thanks,
> 
> Rich
> 

Rich: I haven't followed all this (and probably shouldn't respond) but 
parameter 's' is supposed to be a string, right? Then call it with 
klistcombs("components.in", 2). Are you just missing the quotes?

BTW, it wouldn't be hard to read the file in line by line and do a 
string.split on it to get the two lists.

Holger