Add tag on float imprecision

Adds a tag on float imprecision

1 files changed, 19 insertions, 0 deletions

diff --git a/bot/resources/tags/floats.md b/bot/resources/tags/floats.md
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+**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**
+If you require 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 is an example using the decimal module:
+```python
+>>> from decimal import Decimal
+>>> Decimal('0.1') + Decimal('0.2')
+Decimal('0.3')
+```
+Note that we enter in 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).