PyCents

pycents is a strongly typed Python library for representing and manipulating monetary values with ISO 4217 and custom currencies, explicit rounding semantics and rich formatting options.

• ISO 4217 & custom currencies: built-in support for ISO 4217 currencies with standardized codes and minor-unit definitions. Custom currencies such as cryptocurrencies can be registered at runtime. Some popular cryptocurrencies are pre-registered and ready to use.

• Money uses integer minor units for exact monetary representation.

• Explicit rounding — PyCents use a dual-type architecture for exact and high-precision operations:

  • Money The core immutable type that stores exact monetary values as integer minor units (e.g., cents).
  • UnroundedMoney: A high-precision type designed for complex intermediate calculations without premature rounding.
  • Seamless Integration: Both types work together fluidly in arithmetic. Calling .round() on an UnroundedMoney instance explicitly converts it back into standard Money.

Features

• 100% Test Coverage & Property-Based Testing: Fully covered and rigorously verified using Hypothesis to guarantee mathematical invariants.
• ISO 4217 currency definitions
• Custom currency support with runtime registration
• Pre-registered popular cryptocurrencies
• Immutable Money type
• Precise decimal arithmetic
• Explicit rounding semantics.
• Locale-aware currency formatting
• Pluggable formatting backends
• Custom format specification

Example

from decimal import Decimal

from pycents import Money, UnroundedMoney, formatting, allocation as alloc

# Use a locale-aware formatting backend
formatting.use_backend("babel")  # Other options are: 'std'(default) and 'icu'

rent = Money.from_major(121_555, "USD")
# the '.2c' format field is for displaying in compact notation
# while retaining 2 decimals
print(f"{rent:.2c}")  # Output: $121.56K

# Apply an 8.875% municipal property tax
tax_rate = Decimal("0.08875")

# `tax` is not a Money instance!
tax = rent * tax_rate
assert isinstance(tax, UnroundedMoney)

# At the end the arithmetic pipeling, call round to get a `Money` instance
total = (rent + tax).round()

# allocate the rent among three clients according to a given ratios
shares = alloc.allocate(total, [1000, 2000, 3000])
result = ", ".join(f"{share:.2c}" for share in shares)
print("Allocated Shares:", f"[{result}]")
# Output: Allocated Shares: [$22.06K, $44.11K, $66.17K]

Documentation

Documentation and API reference are available at pycents.readthedocs.io. This is still a work in progress, some guide are complete (Quickstart, formatting and allocation) but still need to be polished.

License

pycents is distributed under the MIT License. See the LICENSE file for details.