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precedence.py
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precedence.py
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"""A module providing information about the necessity of brackets"""
# Default precedence values for some basic types
PRECEDENCE = {
"Lambda":1,
"Relational":20,
"Add":40,
"Mul":50,
"Pow":60,
"Atom":1000
}
# A dictionary assigning precedence values to certain classes. These values are
# treated like they were inherited, so not every single class has to be named
# here.
PRECEDENCE_VALUES = {
"Add" : PRECEDENCE["Add"],
"Pow" : PRECEDENCE["Pow"],
"Relational" : PRECEDENCE["Relational"],
"Sub" : PRECEDENCE["Add"],
}
# Sometimes it's not enough to assign a fixed precedence value to a
# class. Then a function can be inserted in this dictionary that takes
# an instance of this class as argument and returns the appropriate
# precedence value.
# Precedence functions
def precedence_Mul(item):
coeff, rest = item.as_coeff_terms()
if coeff.is_negative:
return PRECEDENCE["Add"]
return PRECEDENCE["Mul"]
def precedence_Rational(item):
if item.p < 0:
return PRECEDENCE["Add"]
return PRECEDENCE["Mul"]
def precedence_Integer(item):
if item.p < 0:
return PRECEDENCE["Add"]
return PRECEDENCE["Atom"]
PRECEDENCE_FUNCTIONS = {
"Integer" : precedence_Integer,
"Mul" : precedence_Mul,
"Rational" : precedence_Rational,
}
def precedence(item):
"""
Returns the precedence of a given object.
"""
if hasattr(item, "precedence"):
return item.precedence
for i in item.__class__.__mro__:
n = i.__name__
if n in PRECEDENCE_FUNCTIONS:
return PRECEDENCE_FUNCTIONS[n](item)
elif n in PRECEDENCE_VALUES:
return PRECEDENCE_VALUES[n]
return PRECEDENCE["Atom"]