type/money.py

   1 #!/usr/bin/env python3
   2
   3 from decimal import Decimal
   4 import re
   5 from typing import Optional, TypeVar, Tuple
   6
   7 import math_utils
   8
   9
  10 T = TypeVar('T', bound='Money')
  11
  12
  13 class Money(object):
  14     """A class for representing monetary amounts potentially with
  15     different currencies.
  16     """
  17
  18     def __init__ (
  19             self,
  20             amount: Decimal = Decimal("0.0"),
  21             currency: str = 'USD',
  22             *,
  23             strict_mode = False
  24     ):
  25         self.strict_mode = strict_mode
  26         if isinstance(amount, str):
  27             ret = Money._parse(amount)
  28             if ret is None:
  29                 raise Exception(f'Unable to parse money string "{amount}"')
  30             amount = ret[0]
  31             currency = ret[1]
  32         if not isinstance(amount, Decimal):
  33             amount = Decimal(float(amount))
  34         self.amount = amount
  35         if not currency:
  36             self.currency: Optional[str] = None
  37         else:
  38             self.currency: Optional[str] = currency
  39
  40     def __repr__(self):
  41         a = float(self.amount)
  42         a = round(a, 2)
  43         s = f'{a:,.2f}'
  44         if self.currency is not None:
  45             return '%s %s' % (s, self.currency)
  46         else:
  47             return '$%s' % s
  48
  49     def __pos__(self):
  50         return Money(amount=self.amount, currency=self.currency)
  51
  52     def __neg__(self):
  53         return Money(amount=-self.amount, currency=self.currency)
  54
  55     def __add__(self, other):
  56         if isinstance(other, Money):
  57             if self.currency == other.currency:
  58                 return Money(
  59                     amount = self.amount + other.amount,
  60                     currency = self.currency
  61                 )
  62             else:
  63                 raise TypeError('Incompatible currencies in add expression')
  64         else:
  65             if self.strict_mode:
  66                 raise TypeError('In strict_mode only two moneys can be added')
  67             else:
  68                 return Money(
  69                     amount = self.amount + Decimal(float(other)),
  70                     currency = self.currency
  71                 )
  72
  73     def __sub__(self, other):
  74         if isinstance(other, Money):
  75             if self.currency == other.currency:
  76                 return Money(
  77                     amount = self.amount - other.amount,
  78                     currency = self.currency
  79                 )
  80             else:
  81                 raise TypeError('Incompatible currencies in add expression')
  82         else:
  83             if self.strict_mode:
  84                 raise TypeError('In strict_mode only two moneys can be added')
  85             else:
  86                 return Money(
  87                     amount = self.amount - Decimal(float(other)),
  88                     currency = self.currency
  89                 )
  90
  91     def __mul__(self, other):
  92         if isinstance(other, Money):
  93             raise TypeError('can not multiply monetary quantities')
  94         else:
  95             return Money(
  96                 amount = self.amount * Decimal(float(other)),
  97                 currency = self.currency
  98             )
  99
 100     def __truediv__(self, other):
 101         if isinstance(other, Money):
 102             raise TypeError('can not divide monetary quantities')
 103         else:
 104             return Money(
 105                 amount = self.amount / Decimal(float(other)),
 106                 currency = self.currency
 107             )
 108
 109     def __float__(self):
 110         return self.amount.__float__()
 111
 112     def truncate_fractional_cents(self):
 113         x = float(self)
 114         self.amount = Decimal(math_utils.truncate_float(x))
 115         return self.amount
 116
 117     def round_fractional_cents(self):
 118         x = float(self)
 119         self.amount = Decimal(round(x, 2))
 120         return self.amount
 121
 122     __radd__ = __add__
 123
 124     def __rsub__(self, other):
 125         if isinstance(other, Money):
 126             if self.currency == other.currency:
 127                 return Money(
 128                     amount = other.amount - self.amount,
 129                     currency = self.currency
 130                 )
 131             else:
 132                 raise TypeError('Incompatible currencies in sub expression')
 133         else:
 134             if self.strict_mode:
 135                 raise TypeError('In strict_mode only two moneys can be added')
 136             else:
 137                 return Money(
 138                     amount = Decimal(float(other)) - self.amount,
 139                     currency = self.currency
 140                 )
 141
 142     __rmul__ = __mul__
 143
 144     #
 145     # Override comparison operators to also compare currency.
 146     #
 147     def __eq__(self, other):
 148         if other is None:
 149             return False
 150         if isinstance(other, Money):
 151             return (
 152                 self.amount == other.amount and
 153                 self.currency == other.currency
 154             )
 155         if self.strict_mode:
 156             raise TypeError("In strict mode only two Moneys can be compared")
 157         else:
 158             return self.amount == Decimal(float(other))
 159
 160     def __ne__(self, other):
 161         result = self.__eq__(other)
 162         if result is NotImplemented:
 163             return result
 164         return not result
 165
 166     def __lt__(self, other):
 167         if isinstance(other, Money):
 168             if self.currency == other.currency:
 169                 return self.amount < other.amount
 170             else:
 171                 raise TypeError('can not directly compare different currencies')
 172         else:
 173             if self.strict_mode:
 174                 raise TypeError('In strict mode, only two Moneys can be compated')
 175             else:
 176                 return self.amount < Decimal(float(other))
 177
 178     def __gt__(self, other):
 179         if isinstance(other, Money):
 180             if self.currency == other.currency:
 181                 return self.amount > other.amount
 182             else:
 183                 raise TypeError('can not directly compare different currencies')
 184         else:
 185             if self.strict_mode:
 186                 raise TypeError('In strict mode, only two Moneys can be compated')
 187             else:
 188                 return self.amount > Decimal(float(other))
 189
 190     def __le__(self, other):
 191         return self < other or self == other
 192
 193     def __ge__(self, other):
 194         return self > other or self == other
 195
 196     def __hash__(self):
 197         return self.__repr__
 198
 199     AMOUNT_RE = re.compile("^([+|-]?)(\d+)(\.\d+)$")
 200     CURRENCY_RE = re.compile("^[A-Z][A-Z][A-Z]$")
 201
 202     @classmethod
 203     def _parse(cls, s: str) -> Optional[Tuple[Decimal, str]]:
 204         amount = None
 205         currency = None
 206         s = s.strip()
 207         chunks = s.split(' ')
 208         try:
 209             for chunk in chunks:
 210                 if Money.AMOUNT_RE.match(chunk) is not None:
 211                     amount = Decimal(chunk)
 212                 elif Money.CURRENCY_RE.match(chunk) is not None:
 213                     currency = chunk
 214         except:
 215             pass
 216         if amount is not None and currency is not None:
 217             return (amount, currency)
 218         elif amount is not None:
 219             return (amount, 'USD')
 220         return None
 221
 222     @classmethod
 223     def parse(cls, s: str) -> T:
 224         chunks = Money._parse(s)
 225         if chunks is not None:
 226             return Money(chunks[0], chunks[1])
 227         raise Exception(f'Unable to parse money string "{s}"')