Prevent expression evaluation in repr()/latex()

[ABOU SAMRA Jean]

Hello everyone,

I am trying to use SymPy for a mathematical projet, where I need expressions to be evaluated step-by-step.

Until now, I have always used, for example, sympify("2+2", evaluate=False) and all was fine.

But now I am trying to reconstruct an expression from another object that I have created and I sometimes get in trouble with the way the `minus` is handled. Let me give an example:

Python 3.8.0a2 (v3.8.0a2:23f4589b4b, Feb 25 2019, 10:59:08)
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from sympy import *
>>> from sympy.abc import *
>>>
>>> e1 = Mul(Integer(2), Integer(5), evaluate=False)
>>> e1 # all fine here
2*5
>>> print(srepr(e1)) # what I expected
Mul(Integer(2), Integer(5))
>>>
>>> e2 = Mul(Integer(-2), Integer(5), evaluate=False) # now with -2 instead of 2
>>> e2 # Hoops!
-10
>>> 

>>> # yet e2 has not been evaluated to Integer(-10) but its repr() above is wrong
>>> print(srepr(e2))
Mul(Integer(-1), Integer(2), Integer(5))
>>> # I'm trying to use expressions in LaTeX documents and there our e2 is still wrong.
... latex(e2)
'- 10'

I'm quite surprised that Mul(Integer(-1), Integer(2), Integer(5))  becomes "-10" when passed through repr(). This is even more surprising:

>>> init_printing()
>>> e2
-2⋅5

How can I prevent the expression to be represented by repr()/latex() in a single integer but keep the -2*5 form?

Many thanks for your help.

Regards,

Jean Abou Samra.

[Oscar Benjamin]

Hi Jean,

What version of SymPy are you using?

This seems to work fine on SymPy master and with the most recent version (1.4):

In [1]: repr(Mul(-1, 2, 5, evaluate=False))
Out[1]: '-2*5'

--
Oscar

[Jean ABOU SAMRA]

Hi,

Le 2 juin 2019 à 21:40, Oscar Benjamin <oscar.j....@gmail.com> a écrit :

Hi Jean,

Thanks for your quick answer.

What version of SymPy are you using?

This seems to work fine on SymPy master and with the most recent version (1.4):

I'm also using 1.4.

In [1]: repr(Mul(-1, 2, 5, evaluate=False))
Out[1]: '-2*5'

True, but…

>>> repr(Mul(-2, 5, evaluate=False))

'-10'

In fact, all the problem lies here:

>>> # same...

... srepr(Mul(-1, 2, 5, evaluate=False))

'Mul(Integer(-1), Integer(2), Integer(5))'

>>> srepr(Mul(-2, 5, evaluate=False))

'Mul(Integer(-1), Integer(2), Integer(5))'

>>> 

>>> # but different

... repr(Mul(-1, 2, 5, evaluate=False))

'-2*5'

>>> repr(Mul(-2, 5, evaluate=False)) # Hoops!

'-10'

>>> 

>>> # even weirder

... init_printing()

>>> Mul(-1, 2, 5, evaluate=False)

-2⋅5

>>> Mul(-2, 5, evaluate=False) # here all is fine!

-2⋅5

Kind regards,

Jean Abou Samra

[Aaron Meurer]

There have been bugs in the past where printers evaluate
evaluate=False expressions. It looks like there is another such bug
here. Can you open an issue for this?

Aaron Meurer

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[Jean ABOU SAMRA]

Done!

https://github.com/sympy/sympy/issues/16955

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