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Changed Printing of Logic Expressions #11448

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Changed Printing of Logic Expressions #11448

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9b0a842
Changed printing of logic expressions
arihantparsoya Jul 29, 2016
1986613
Improved parenthesization in Logical Expressions
arihantparsoya Aug 12, 2016
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7 changes: 5 additions & 2 deletions sympy/printing/str.py
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Expand Up @@ -75,13 +75,16 @@ def _print_BooleanFalse(self, expr):
return "False"

def _print_And(self, expr):
return '%s(%s)' % (expr.func, ', '.join(sorted(self._print(a) for a in
return '(%s)' % (' & '.join(sorted(self._print(a) for a in
expr.args)))

def _print_Or(self, expr):
return '%s(%s)' % (expr.func, ', '.join(sorted(self._print(a) for a in
return '(%s)' % (' | '.join(sorted(self._print(a) for a in
expr.args)))

def _print_Not(self, expr):
return '%s(%s)' % ('~', self._print(expr.args[0]))

def _print_AppliedPredicate(self, expr):
return '%s(%s)' % (expr.func, expr.arg)

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6 changes: 3 additions & 3 deletions sympy/printing/tests/test_str.py
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Expand Up @@ -660,14 +660,14 @@ def test_settings():
def test_RandomDomain():
from sympy.stats import Normal, Die, Exponential, pspace, where
X = Normal('x1', 0, 1)
assert str(where(X > 0)) == "Domain: And(0 < x1, x1 < oo)"
assert str(where(X > 0)) == "Domain: (0 < x1 & x1 < oo)"

D = Die('d1', 6)
assert str(where(D > 4)) == "Domain: Or(Eq(d1, 5), Eq(d1, 6))"
assert str(where(D > 4)) == "Domain: (Eq(d1, 5) | Eq(d1, 6))"

A = Exponential('a', 1)
B = Exponential('b', 1)
assert str(pspace(Tuple(A, B)).domain) == "Domain: And(0 <= a, 0 <= b, a < oo, b < oo)"
assert str(pspace(Tuple(A, B)).domain) == "Domain: (0 <= a & 0 <= b & a < oo & b < oo)"
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You need to be more careful about parenthesization. This is wrong (needs parentheses around the inequalities).

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is this output desirable?

>>> from sympy import *
>>> from sympy.abc import x,y,z
>>> print(And(Not(x), Or(y, z)))
((((y) | (z))) & (~(x)))

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IMHO, I don't think that is desirable.
Is it possible to parenthesize only when necessary, depending on operator precedence?

I would suggest you take a look at the parethesize method of the StrPrinter class.
(https://github.com/sympy/sympy/blob/master/sympy/printing/str.py#L27)

Personally, I think this would be desirable:

>>> print(And(Not(x), Or(y, z)))
(y | z) & ~x

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I am able to get the output using the parethesize method method. But I am unable to parenthesize inequalities as desired. Any tips?

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I assume you used the precedence function, which follows this precedence table:
https://github.com/sympy/sympy/blob/master/sympy/printing/precedence.py#L8

Do we really need parentheses around the inequalities in that case? Don't relational operators have precedence over logical And? (at least from a programming language perspective)

However, this does look more appealing:

"Domain: (0 <= a) & (0 <= b) & (a < oo) & (b < oo)"

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Do we really need parentheses around the inequalities in that case? Don't relational operators have precedence over logical And? (at least from a programming language perspective)

No they don't. That's why parentheses are so important.

In [71]: type(x < y & z)
Out[71]: sympy.core.relational.StrictLessThan

In [72]: x < (y & z)
Out[72]: x < y ∧ z

In [73]: (x < y) & z
Out[73]: z ∧ x < y

In [74]: (x < y & z).args
Out[74]: (x, y ∧ z)

See also https://docs.python.org/3/reference/expressions.html#operator-precedence

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Honestly, I find the behavior in the example above odd. I would expect the following results to be equal:

>>> srepr(x < y & z)
"StrictLessThan(Symbol(′x′),And(Symbol(′y′),Symbol(′z′)))"

>>> srepr((x < y) & z)
"And(Symbol(′z′),StrictLessThan(Symbol(′x′),Symbol(′y′)))"

As for the python reference, it agrees with what I was trying to say in my previous answer.

>>> 2 > 2 and True
False

>>> (2 > 2) and True
False

>>> 2 > (2 and True)
True

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@gorisaka do not confuse and and &. The former has lower precedence than the inequality operators, and can't be overridden by libraries like SymPy. & has higher precedence and can be overridden.

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Since | is also overridden the same problem occurs with it:

>>> str((x > 1) | (x < -1))
x > 1 | x < -1



def test_FiniteSet():
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