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"""
"""
import ast
import re
class UnitRegistry:
# Note that this structure ensures that UnitRegistry behaves as a singleton
class __Registry:
__shared_state = {}
whitelist = (
ast.Expression,
ast.Constant,
ast.Name,
ast.Load,
ast.BinOp,
ast.UnaryOp,
ast.operator,
ast.unaryop,
)
def __init__(self):
self.__dict__ = self.__shared_state
self.__context = {}
def __getitem__(self, string):
# This approach to avoiding arbitrary evaluation of code is based on https://stackoverflow.com/a/11952618
# by https://stackoverflow.com/users/567292/ecatmur
tree = ast.parse(string, mode="eval")
valid = all(isinstance(node, self.whitelist) for node in ast.walk(tree))
if valid:
try:
item = eval(
compile(tree, filename="", mode="eval"),
{"__builtins__": {}},
self.__context,
)
except NameError:
raise LookupError('Unable to parse units: "%s"' % string)
else:
return item
else:
# could return self['UnitQuantity'](string)
raise LookupError('Unable to parse units: "%s"' % string)
def __setitem__(self, string, val):
assert isinstance(string, str)
try:
assert string not in self.__context
except AssertionError:
if val == self.__context[string]:
return
raise KeyError(
'%s has already been registered for %s'
% (string, self.__context[string])
)
self.__context[string] = val
__regex = re.compile(r'([A-Za-z])\.([A-Za-z])')
__registry = __Registry()
def __getattr__(self, attr):
return getattr(self.__registry, attr)
def __setitem__(self, label, value):
self.__registry.__setitem__(label, value)
def __getitem__(self, label):
"""Parses a string description of a unit e.g., 'g/cc'"""
label = self.__regex.sub(
r"\g<1>*\g<2>", label.replace('^', '**').replace('ยท', '*'))
# make sure we can parse the label ....
if label == '': label = 'dimensionless'
if "%" in label: label = label.replace("%", "percent")
if label.lower() == "in": label = "inch"
return self.__registry[label]
unit_registry = UnitRegistry()
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