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boundary="1679980782-407868024-1397106764=:87133" X-Mailman-Approved-At: Thu, 10 Apr 2014 08:47:40 +0200 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Kim Plofker List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 121 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1397112461 news.xs4all.nl 2975 [2001:888:2000:d::a6]:35601 X-Complaints-To: abuse@xs4all.nl X-Received-Body-CRC: 961477212 X-Received-Bytes: 15235 Xref: csiph.com comp.lang.python:70017 --1679980782-407868024-1397106764=:87133 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Thanks! =A0As I recently posted in a followup message,=0A=0A--------=0AHere= 's an example of what goes wrong:=0A=0At =3D var('t')=0A=0AL(t) =3D t*725.5= %360.0=0A=0A=0AThis produces the following error message:=0A=0A...=0ATypeEr= ror: unsupported operand type(s) for %:=0A'sage.symbolic.expression.Express= ion' and=0A'sage.symbolic.expression.Expression'=0A--------=0A=0A=0ASo it l= ooks like I've got a Sage-specific problem. =A0I still don't know how to fi= x it, but at least I understand the problem better! =A0=0A=0AMany thanks,= =0AKim=0A=0A________________________________=0A From: Steven D'Aprano =0ATo: python-list@python.org =0ASent: Thursday, April 10, = 2014 1:01 AM=0ASubject: Re: Plotting the integer-and-fraction remainder of = a function value modulo 360=0A =0A=0AOn Wed, 09 Apr 2014 21:32:27 -0700, Ki= m Plofker wrote:=0A=0A> How can I get Python to represent a value of a func= tion in degrees,=0A> i.e., with values between 0 and 360, by taking the (no= n-integer)=0A> function expression mod 360?=0A> =0A> That is, I have a func= tion with non-integer values, called Longitude,=0A> which is defined in ter= ms of the variable t. I just want to plot=0A> Longitude modulo 360 for a ra= nge of values of t: that is, for every=0A> value of t, plot the integer-AND= -fraction remainder after dividing=0A> Longitude by 360.=0A> =0A> But Pytho= n (in Sage) apparently won't let me use the int function or the=0A> // oper= ator on functions defined in terms of a variable: I get a "cannot=0A> evalu= ate symbolic expression numerically" TypeError. =0A=0AThat's an issue with = Sage itself, probably sympy. Python the language =0Adoesn't natively unders= tand symbolic expressions, that's added by sympy, =0Aso you may need to ask= some sympy experts.=0A=0AIt may help if you show the actual code you are u= sing, and the full =0Atraceback generated by the error. When I try somethin= g similar, I get a =0Adifferent error message:=0A=0Apy> from sympy.abc impo= rt x=0Apy> (x + 1) % 60=0ATraceback (most recent call last):=0A=A0 File "", line 1, in =0ATypeError: unsupported operand type(s) for %:= 'Add' and 'int'=0A=0A=0Awhich could mean I'm doing something different, or= just a difference in =0Aversion numbers.=0A=0A=0A> How do I do this?=0A> T= here must be a simple way to tell Python that I want it to compute the=0A> = value of Longitude for a given value of t and then take the=0A> integer-and= -fraction remainder from dividing by 360.=0A=0AThat's simple with numeric t= ypes: use the divmod function or % operator. =0ABut you're using some sort = of symbolic library, so we need to know what =0Athe library is.=0A=0A=0A-- = =0ASteven=0A-- =0Ahttps://mail.python.org/mailman/listinfo/python-list --1679980782-407868024-1397106764=:87133 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Thanks!  As I recently posted in a followup m= essage,
-------= -
Here's an= example of what goes wrong:

t =3D var('t')
L(t) =3D t*725.5%360.0

This produces the following error message:

...=0ATypeError: unsupported operand type(s) for %:=
=0A'sage.symbolic.expression.Expression' and=0A'sage.symbolic.expression.Ex=
pression'
--------

So it looks like I've got a Sage-specific problem.=  I still don't know how to fix it, but at least I understand the prob= lem better!  

=
Many thanks,
K= im
From: Steven D'Aprano <steve@pearwood.info>
To: python-list@python.org
Sent: Thursday, April 10, 2014 1:01 AM=
Subject: Re: Plotting= the integer-and-fraction remainder of a function value modulo 360

On Wed, 09 Apr 2014 21:32:27 = -0700, Kim Plofker wrote:

> How can I get Python to represent a v= alue of a function in degrees,
> i.e., with values between 0 and 360, by takin= g the (non-integer)
> function expression mod 360?
>
> T= hat is, I have a function with non-integer values, called Longitude,
>= ; which is defined in terms of the variable t. I just want to plot
> = Longitude modulo 360 for a range of values of t: that is, for every
>= value of t, plot the integer-AND-fraction remainder after dividing
>= Longitude by 360.
>
> But Python (in Sage) apparently won't l= et me use the int function or the
> // operator on functions defined = in terms of a variable: I get a "cannot
> evaluate symbolic expressio= n numerically" TypeError.

That's an issue with Sage itself, probabl= y sympy. Python the language
doesn't natively understand symbolic expre= ssions, that's added by sympy,
so you may need to ask some sympy expert= s.

It may help if you show the actual code you are using, and the full
traceback generated by the error. When I try something simila= r, I get a
different error message:

py> from sympy.abc import= x
py> (x + 1) % 60
Traceback (most recent call last):
  F= ile "<stdin>", line 1, in <module>
TypeError: unsupported op= erand type(s) for %: 'Add' and 'int'


which could mean I'm doing = something different, or just a difference in
version numbers.

> How do I do this?
> There must be a simple way to tell Python = that I want it to compute the
> value of Longitude for a given value = of t and then take the
> integer-and-fraction remainder from dividing= by 360.

That's simple with numeric types: use the divmod function o= r % operator.
But you're using some sort of symbolic library, so we nee= d to know what
the library is.


--
Steven
--
https://mail.python.org/mailman/listinfo/python-list=


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