[Python-3000] Announcing PEP 3136 (original) (raw)

Terry Reedy tjreedy at udel.edu
Wed Jul 4 01:40:14 CEST 2007

"John S. Yates, Jr." <john at yates-sheets.org> wrote in message news:j1gk83hfeltf7uqi0u4b5tpgbg80qg3cp0 at 4ax.com... | On Tue, 3 Jul 2007, "Guido van Rossum" <guido at python.org> wrote: || >However, I'm rejecting it on the basis that code so complicated to | >require this feature is very rare. || I assume that you are familiar with Donald E. Knuth's classic paper: | "Structured Programming with go to Statements" | http://pplab.snu.ac.kr/courses/advpl05/papers/p261-knuth.pdf

Do you consider this to be for or against the PEP? Rereading it....

At least half Knuth's goto examples are covered by Python's single level restricted gotos:

Example 1 (switched to 0-bases arrays, not tested):

for i in range(m): if A[i] == x: break else: A[m] = x B[m] = 0 m += 1 B[i] += 1

Example 5 (ditto):

i = 0 #? initial value not given while True: if A[i] < x: if L[i] != 0: i = L[i]; continue else: L[i] = j; break else: # > x if R[i] != 0: i = R[i]; continue else: R[i] = j; break # dup code could be factored with LR = L or R as A[i] < or > x A[j] = x L[j] = R[j] = 0 j += 1

The rest are general gotos, including jumps into the middle of loops. None are multilevel continues or breaks.

tjr

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