Re: for what are for/while else clauses

From: Mel Wilson (mwilson_at_the-wire.com)
Date: 11/20/03

  • Next message: Mel Wilson: "Re: Python's simplicity philosophy" 
    Date: Wed, 19 Nov 2003 21:14:27 -0500

    In article <mailman.787.1069069214.702.python-list@python.org>,
    "Fredrik Lundh" <fredrik@pythonware.com> wrote:
    >for a while-statement, the controlling condition is the test at
    >the top.
    >
    >for a for loop, the condition is "is there another item" (to quote the
    >language reference: "When the items are exhausted (which is imme-
    >diately when the sequence is empty) ... the loop terminates.".
    >
    >for a try-except clause, the condition is "did the suite raise an
    >exception".

       Interesting way to think about it. Thanks.

       So in some sample code:

            while some_condition:
                some_action ()
            else:
                last_action ()
            following_code ()

    If the loop results in some_action being done, say, 17
    times; then that means that some_condition was found true 17
    times. The 18th time, some_condition is found to be false,
    the else takes effect and last_action gets done one time.
    The only wrinkle then is that the while loop construct
    passes control to the following code after that one
    last_action. But we expect that from a while loop.

       The effect of a break in the suite controlled by the
    while is to blow away execution of the whole while
    construct, including the else.

       As an explanation, I like it.

            Regards. Mel.

  • Next message: Mel Wilson: "Re: Python's simplicity philosophy"

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