PEP 276 Simple Iterator for ints

David Eppstein eppstein at ics.uci.edu
Tue Nov 13 23:22:50 CET 2001


As a possibly-related side note to this debate:

I have been moving towards using Python-like pseudocode in my algorithms 
classes in place of the C/C++/Java-like pseudocode I was previously using; 
that is, using colons and indentation to mark blocks of code instead of 
curly braces, etc.  As well as conciseness, Python offers some other 
advantages e.g. in the ability to write code with list comprehensions.
The single biggest barrier for me to write actual working Python code is 
the range/xrange syntax: I just don't feel comfortable writing code like

    for i in range(n-1,-1,-1):
       for j in range(i+1,n+1):
            ...do something...

because I don't expect my students (who are not required to learn Python) 
to understand from that syntax that the outer loop runs backwards from n-1 
to 0 and that the inner loop runs from i+1 to n.

Instead I have to make up some non-Python syntax which is less formal but 
immediately clear:

    for i in [n-1, n-2, ... 0]:
        for j in [i+1, i+2, ... n]:
            ...do something...

(actual example from <http://www.ics.uci.edu/~eppstein/260/011023/>).
As far as I can see, the PEP under discussion (which simply replaces the 
word "range" by "iter", creates an iterator instead of a list, and perhaps 
only allows the single-argument version of range) doesn't help me at all in 
my desire to have lecture notes which are both intuitively understandable 
and runnable.
-- 
David Eppstein       UC Irvine Dept. of Information & Computer Science
eppstein at ics.uci.edu http://www.ics.uci.edu/~eppstein/



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