The culprit here is fraction() from the simplify module, which expands the Mul() expression, ignoring the evaluate=False parameter. There is a simple fix, which is to use the original expression rather than the (modified) numerator. One could ask whether fraction() should respect the evaluate=False parameter or not. It is part of the "simplify" module after all. Then again, it is quite possible to apply fraction to unevaluated Mul object in a way that maintains the unevaluated property.
https://github.com/sympy/sympy/pull/2617 On Tuesday, November 19, 2013 10:26:59 PM UTC-5, Aaron Meurer wrote: > > Yes, unfortunately, unevaluated expressions tend to be "unstable". > Sometimes things will do what would normally be an innocuous > transformation that ends up evaluating it. These bugs have been mostly > fixed for the pretty printer, but I guess they are still there for the > latex printer. > > Aaron Meurer > > On Mon, Nov 18, 2013 at 4:30 AM, <[email protected] <javascript:>> > wrote: > > Hi, > > > > I work with unevaluated Adds and Muls and today found this: > > > >>>> from sympy import latex, Mul, Symbol > >>>> x = Symbol('x') > >>>> e = Mul(-2, x + 1, evaluate=False) > >>>> print e > > -2*(x + 1) > >>>> print latex(e) > > - 2 x + 2 > > > > The first print is correct but the second one is not. It's not about > simply > > dropping parentheses when they are needed. In that case the second print > > would read - 2 x + 1 so some computation took place. > > > > Regards > > -- > > Greg > > > > -- > > You received this message because you are subscribed to the Google > Groups > > "sympy" group. > > To unsubscribe from this group and stop receiving emails from it, send > an > > email to [email protected] <javascript:>. > > To post to this group, send email to [email protected]<javascript:>. > > > Visit this group at http://groups.google.com/group/sympy. > > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out.
