Python as a Calculator
Arithmetic Operators
Operator  Operation  Expression  English description  Result 
+ 
addition  11 + 56 
11 plus 56  67 
 
subtraction  23  52 
23 minus 52  29 
* 
multiplication  4 * 5 
4 multiplied by 5  20 
** 
exponentiation  2 ** 5 
2 to the power of 5  32 
/ 
division  9 / 2 
9 divided by 2  4.5 
// 
integer division  9 // 2 
9 divided by 2  4 
% 
modulo (remainder)  9 % 2 
9 mod 2  1 
Types int
and float
A type is a set of values and operations that can be performed on those values.
Two of Python's numeric types:

int
: integer
For example:3
,4
,894
,0
,3
,18

float
: floating point number (an approximation to a real number)
For example:5.6
,7.342
,53452.0
,0.0
,89.34
,9.5
Arithmetic Operator Precedence
When multiple operators are combined in a single expression, the operations are evaluated in order of precedence.
Operator  Precedence 
**  highest 
 (negation)  
*, /, //, %  
+ (addition),  (subtraction)  lowest 
Syntax and Semantics
Syntax: the rules that describe valid combinations of Python symbols
Semantics: the meaning of a combination of Python symbols is the meaning of an instruction — what a particular combination of symbols does when you execute it.
Errors
A syntax error occurs when we an instruction with invalid syntax is executed. For example:
>>> 3) + 2 * 4 SyntaxError: invalid syntax
A semantic error occurs when an instruction with invalid semantics is executed. For example:
>>> 89.4 / 0 Traceback (most recent call last): File "", line 1, in 89.4 / 0 ZeroDivisionError: float division by zero