Add tag on float imprecision

bot/resources/tags/floats.md

@@ -0,0 +1,20 @@
+**Floating Point Arithmetic**
+You may have noticed that when doing arithmetic with floats in Python you sometimes get strange results, like this:
+```python
+>>> 0.1 + 0.2
+0.30000000000000004
+```
+**Why this happens**
+Internally your computer stores floats as as binary fractions. Many decimal values cannot be stored as exact binary fractions, which means an approximation has to be used.
+
+**How you can avoid this**
+ You can use [math.isclose](https://docs.python.org/3/library/math.html#math.isclose) to check if two floats are close, or to get an exact decimal representation, you can use the [decimal](https://docs.python.org/3/library/decimal.html) or [fractions](https://docs.python.org/3/library/fractions.html) module. Here are some examples:
+```python
+>>> math.isclose(0.1 + 0.2, 0.3)
+True
+>>> decimal.Decimal('0.1') + decimal.Decimal('0.2')
+Decimal('0.3')
+```
+Note that with `decimal.Decimal` we enter the number we want as a string so we don't pass on the imprecision from the float.
+
+For more details on why this happens check out this [page in the python docs](https://docs.python.org/3/tutorial/floatingpoint.html) or this [Computerphile video](https://www.youtube.com/watch/PZRI1IfStY0).