Merge pull request sympy#8475 from skirpichev/8470-fix

Improve _needs_mul_brackets: place brackets around Mul, if it starts from "-"

Author: skirpichev

sympy/printing/latex.py

@@ -194,17 +194,30 @@ def _needs_function_brackets(self, expr):
             else:
                 return False
 
-    def _needs_mul_brackets(self, expr, last=False):
+    def _needs_mul_brackets(self, expr, first=False, last=False):
         """
         Returns True if the expression needs to be wrapped in brackets when
         printed as part of a Mul, False otherwise. This is True for Add,
         but also for some container objects that would not need brackets
         when appearing last in a Mul, e.g. an Integral. ``last=True``
         specifies that this expr is the last to appear in a Mul.
+        ``first=True`` specifies that this expr is the first to appear in a Mul.
         """
         from sympy import Integral, Piecewise, Product, Sum
-        return expr.is_Add or (not last and
-            any([expr.has(x) for x in (Integral, Piecewise, Product, Sum)]))
+
+        res = False
+
+        if expr.is_Add:
+            return True
+        elif expr.is_Mul:
+            if not first and _coeff_isneg(expr):
+                return True
+
+        if (not last and
+            any([expr.has(x) for x in (Integral, Piecewise, Product, Sum)])):
+            return True
+
+        return res
 
     def _mul_is_clean(self, expr):
         for arg in expr.args:
@@ -269,13 +282,11 @@ def _print_Float(self, expr):
             return str_real
 
     def _print_Mul(self, expr):
-        coeff, _ = expr.as_coeff_Mul()
-
-        if not coeff.is_negative:
-            tex = ""
-        else:
+        if _coeff_isneg(expr):
             expr = -expr
             tex = "- "
+        else:
+            tex = ""
 
         from sympy.simplify import fraction
         numer, denom = fraction(expr, exact=True)
@@ -296,7 +307,8 @@ def convert(expr):
                 for i, term in enumerate(args):
                     term_tex = self._print(term)
 
-                    if self._needs_mul_brackets(term, last=(i == len(args) - 1)):
+                    if self._needs_mul_brackets(term, first=(i == 0),
+                                                last=(i == len(args) - 1)):
                         term_tex = r"\left(%s\right)" % term_tex
 
                     if re.search("[0-9][} ]*$", last_term_tex) and \

sympy/printing/tests/test_latex.py

@@ -1301,3 +1301,9 @@ def test_issue_7180():
 
 def test_issue_8409():
     assert latex(S.Half**n) == r"\left(\frac{1}{2}\right)^{n}"
+
+
+def test_issue_8470():
+    from sympy.parsing.sympy_parser import parse_expr
+    e = parse_expr("-B*A", evaluate=False)
+    assert latex(e) == r"A \left(- B\right)"