Is time.time() < time.time() always true?

Discussion in 'Python' started by flamesrock, Nov 21, 2006.

  1. flamesrock

    flamesrock Guest

    So, I was blazin' some mad chronix, as they say, and got on to thinking
    about Python.

    The question was, is the statement:

    time.time() < time.time()

    always true? Seems it should be false, since the statement itself
    occurs at one time instant.. but of course we know that python doesn't
    execute code that way.. So my question is, why doesn't Python work this
    way?


    (PS, I wasn't smoking anything, its a figure of speech :) )
    flamesrock, Nov 21, 2006
    #1
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  2. flamesrock

    Chris Mellon Guest

    On 21 Nov 2006 15:10:25 -0800, flamesrock <> wrote:
    > So, I was blazin' some mad chronix, as they say, and got on to thinking
    > about Python.
    >
    > The question was, is the statement:
    >
    > time.time() < time.time()
    >
    > always true? Seems it should be false, since the statement itself
    > occurs at one time instant.. but of course we know that python doesn't
    > execute code that way.. So my question is, why doesn't Python work this
    > way?
    >


    This would only be false if the time between the 2 calls was less than
    the precision of the OS call that time.time uses.
    Chris Mellon, Nov 21, 2006
    #2
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  3. flamesrock wrote:

    > always true? Seems it should be false, since the statement itself
    > occurs at one time instant.. but of course we know that python
    > doesn't execute code that way..


    C++ also wouldn't. How could multiple object instantiations be
    atomic?

    Regards,


    Björn

    --
    BOFH excuse #42:

    spaghetti cable cause packet failure
    Bjoern Schliessmann, Nov 21, 2006
    #3
  4. At Tuesday 21/11/2006 20:10, flamesrock wrote:

    >The question was, is the statement:
    >
    >time.time() < time.time()
    >
    >always true? Seems it should be false, since the statement itself
    >occurs at one time instant.. but of course we know that python doesn't
    >execute code that way.. So my question is, why doesn't Python work this
    >way?


    The only thing Python can guarantee, is that the left expression is
    evaluated before the right one (5.13 Evaluation order, Language Reference).

    Then, whether the first call yields a result always less (or equal)
    to the second, is out of Python scope (and control).
    (They might be equal if both calls get the same quantum of time; they
    might be reversed if some other process sets the time in the past).


    --
    Gabriel Genellina
    Softlab SRL

    __________________________________________________
    Correo Yahoo!
    Espacio para todos tus mensajes, antivirus y antispam ¡gratis!
    ¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar
    Gabriel Genellina, Nov 22, 2006
    #4
  5. flamesrock

    Ben Finney Guest

    Gabriel Genellina <> writes:

    > The only thing Python can guarantee, is that the left expression is
    > evaluated before the right one (5.13 Evaluation order, Language
    > Reference).


    Thanks, that answers my question asked elsewhere.

    --
    \ "One thing vampire children have to be taught early on is, |
    `\ don't run with a wooden stake." -- Jack Handey |
    _o__) |
    Ben Finney
    Ben Finney, Nov 22, 2006
    #5
  6. flamesrock

    AndyR Guest

    Hi all:

    From my experience with os's.
    Time is updated at intervals- they may be as low as 1mS See . So for that
    millisecond multiple readings of the time will always return the same
    result. Therefore time.time() < time.time() will be false for most readings.

    However the result could be true if you catch the exact time when the os
    updates its clock. It will only be True for a single execution of the line
    and you will have to be lucky to catch it at just the right time.

    Of course if you hard loop over the interval its possible to see the
    transition.

    for x in xrange (10000):
    t = time.time()
    if t < time.time:
    print "transition at ", t

    Enjoy.
    Andy

    "Ben Finney" <> wrote in message
    news:...
    > Gabriel Genellina <> writes:
    >
    >> The only thing Python can guarantee, is that the left expression is
    >> evaluated before the right one (5.13 Evaluation order, Language
    >> Reference).

    >
    > Thanks, that answers my question asked elsewhere.
    >
    > --
    > \ "One thing vampire children have to be taught early on is, |
    > `\ don't run with a wooden stake." -- Jack Handey |
    > _o__) |
    > Ben Finney
    >
    AndyR, Nov 22, 2006
    #6
  7. "flamesrock" <> wrote:

    8<----------------------------------

    > .... since the statement itself
    > occurs at one time instant..


    nothing, but nothing, can occur at one time instant....

    - Hendrik
    Hendrik van Rooyen, Nov 22, 2006
    #7
  8. flamesrock

    Tim Roberts Guest

    "Hendrik van Rooyen" <> wrote:

    >"flamesrock" <> wrote:
    >
    >8<----------------------------------
    >
    >> .... since the statement itself
    >> occurs at one time instant..

    >
    >nothing, but nothing, can occur at one time instant....


    Well, as long as we're being pedantic, surely that should read "only one
    thing can occur at any time instant..."
    --
    Tim Roberts,
    Providenza & Boekelheide, Inc.
    Tim Roberts, Nov 23, 2006
    #8
  9. "Tim Roberts" <> wrote:


    > "Hendrik van Rooyen" <> wrote:
    >
    > >"flamesrock" <> wrote:
    > >
    > >8<----------------------------------
    > >
    > >> .... since the statement itself
    > >> occurs at one time instant..

    > >
    > >nothing, but nothing, can occur at one time instant....

    >
    > Well, as long as we're being pedantic, surely that should read "only one
    > thing can occur at any time instant..."


    No its worse than that - what I mean is that everything takes finite time...

    :) Hendrik
    Hendrik van Rooyen, Nov 24, 2006
    #9
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