Create decimal_quantize.md

python/decimal_quantize.md

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+# Using `Decimal.quantize` 
+
+## Links 
+
+- [decimal — Decimal fixed point and floating point arithmetic — Python 3.12.4 documentation](https://docs.python.org/3/library/decimal.html)
+
+## `quantize` 
+
+From the docs: 
+
+> The quantize() method rounds a number to a fixed exponent. This method is useful for monetary applications that often round results to a fixed number of places:
+
+```python
+from decimal import Decimal
+
+Decimal('7.325').quantize(Decimal('.01'), rounding=ROUND_DOWN)
+Decimal('7.32')
+
+Decimal('7.325').quantize(Decimal('1.'), rounding=ROUND_UP)
+Decimal('8')
+```
+
+## Notes
+
+You have to call `quantize` on a `Decimal` object. You also pass it another `Decimal` object. The number of decimal places in the `Decimal` you pass to `quantize` determines the number of decimal places in your result. 
+
+To use this with money, you might have something like: 
+
+```python
+>>> from decimal import Decimal
+>>> Decimal(1989)
+Decimal('1989')
+>>> Decimal(1989).quantize(Decimal("00"))
+Decimal('1989')
+>>> Decimal(1989).quantize(Decimal(".00"))
+Decimal('1989.00')
+>>> Decimal(19.89).quantize(Decimal(".00"))
+Decimal('19.89')
+>>> Decimal(19.89).quantize(Decimal(".013"))
+Decimal('19.890')
+```
+
+I don't love working with Decimals. But needs must, and discovering `quantize` was nice.