Update README.md

Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>

python_basics/basic_math_operations/README.md

@@ -203,6 +203,54 @@ print(math.cos(math.pi))​
 
 
 
+## [Behind the curtain ](https://docs.python.org/3/library/operator.html)
+
+{: .topic-optional}
+This is an optional topic!
+
+If you do a + b, in reality this is internally replaced by add(a, b). 
+
+These are the ["Mapping Operators to Functions"](https://docs.python.org/3/library/operator.html#mapping-operators-to-functions):
+
+|Operation|Syntax|Function|
+|---|---|---|
+|Addition|a + b|add(a, b)|
+|Concatenation|seq1 + seq2|concat(seq1, seq2)|
+|Containment Test|obj in seq|contains(seq, obj)|
+|Division|a / b|truediv(a, b)|
+|Division|a // b|floordiv(a, b)|
+|Bitwise And|a & b|and_(a, b)|
+|Bitwise Exclusive Or|a ^ b|xor(a, b)|
+|Bitwise Inversion|~ a|invert(a)|
+|Bitwise Or|a \| b|or_(a, b)|
+|Exponentiation|a ** b|pow(a, b)|
+|Identity|a is b|is_(a, b)|
+|Identity|a is not b|is_not(a, b)|
+|Indexed Assignment|obj[k] = v|setitem(obj, k, v)|
+|Indexed Deletion|del obj[k]|delitem(obj, k)|
+|Indexing|obj[k]|getitem(obj, k)|
+|Left Shift|a << b|lshift(a, b)|
+|Modulo|a % b|mod(a, b)|
+|Multiplication|a * b|mul(a, b)|
+|Matrix Multiplication|a @ b|matmul(a, b)|
+|Negation (Arithmetic)|- a|neg(a)|
+|Negation (Logical)|not a|not_(a)|
+|Positive|+ a|pos(a)|
+|Right Shift|a >> b|rshift(a, b)|
+|Slice Assignment|seq[i:j] = values|setitem(seq, slice(i, j), values)|
+|Slice Deletion|del seq[i:j]|delitem(seq, slice(i, j))|
+|Slicing|seq[i:j]|getitem(seq, slice(i, j))|
+|String Formatting|s % obj|mod(s, obj)|
+|Subtraction|a - b|sub(a, b)|
+|Truth Test|obj|truth(obj)|
+|Ordering|a < b|lt(a, b)|
+|Ordering|a <= b|le(a, b)|
+|Equality|a == b|eq(a, b)|
+|Difference|a != b|ne(a, b)|
+|Ordering|a >= b|ge(a, b)|
+|Ordering|a > b|gt(a, b)|
+
+