An antipattern using the pint unit representation system.

pint-problem

from pint import UnitRegistry

ureg = UnitRegistry()

x = [ureg['1m'], ureg['1m'], ureg['1m']]
y = [ureg['1m']] * 3

try:
  print(sum(y))
except:
  # pint.unit.DimensionalityError: Cannot convert from 'meter' to 'dimensionless'
  pass

# Oops! OK, so...
def summer(values):
  if not values:
    return 0
  total = values[0]
  for v in values[1:]:
    total += v
  return total

print(summer(x))
# 3 meter    Good, it works...

print(summer(y))
# 4 meter    Huh?

print(x)
# [<Quantity(3, 'meter')>, <Quantity(1, 'meter')>, <Quantity(1, 'meter')>]

print(y)
# [<Quantity(4, 'meter')>, <Quantity(4, 'meter')>, <Quantity(4, 'meter')>]