Python Variables and Python Assignment Statement
Variable associates a name with a value. Through variable you can store information.
Variables are nothing but reserved memory locations to store values.
When a variable is created, it reserves some space in memory.
Based upon the data type of a variable, the interpreter of Python allocates memory and decides
what can be stored in the reserved memory. Therefore, the integers,decimals or characters
can be stored by assigning different data types to variables, user need to
be mindful while choosing names for your variables. Some name such as if,
else, print etc are already reserved. Python Variable names can be lower case and uppercase.
A Python variable can be made using letters,numbers and underscores, however Python variable can not start with a number.
Python Variables receive their initial values and can be reset to new values with an Python assignment statement.
The form of an Python assignment statement is the following:
<variable name>= < expression >
money = 100
meter = 1000.0
name = "mohit"
Python Multiple Assignment
Python allows you to assign a single value to several Python variables simultaneously. For example:
a = b = c = 1
Python Numeric Data Types
Python allows programmers to use several different types of numbers. The two types used in
this program are integer and floating point numbers. The integers include 0,
all of the positive whole numbers, and all of the negative whole numbers
The Python interpreter first checks the expression on the right side of the assignment
operator and then binds the value with its variable name, it is called defining or initializing the Python variable.
Python integer data type consists of the integers ranges from -2^31 to 2^31-1 the leading minus sign
shows the negative values. When the integer's values exceeds these limit then Python interpreter automatically uses
the long data type to and put "L"
at the end of integer to represent it as shown in figure below.
Python Floating-Point Numbers
Python uses floating-point numbers to represent real numbers. Values of the most common.
Python Character Sets
Python characters look like string,the below figure shows the mapping of character set
Mapping of Python character values
The above figures is showing the mapping of first 128 ASCII codes to character values.
The left column digits are the leftmost digit of ASCII code.
The Top row's digits represent rightmost digits.
For example to glean ASCII code of charcter "L
" would be 76,
Python Conversion functions
If you want to convert character value to ASCII code use ord()
function and if you want to convert ASCII code character use chr()
function as shown in figure below.
Python Arithmetic Expressions
Python Arithmetic Expressions comprises operands and operators. Consider x and y are two operands having value 10 and 20 respectively.
|**||Exponent - Performs exponential (power) calculation on operators |
|*||Multiplication - Multiplies values on either side of the operator|
|/||Division - Divides left hand operand by right hand operand |
|%||Modulus - Divides left hand operand by right hand operand and returns remainder |
|+||Addition - Adds values on either side of the operator |
|-||Subtraction - Subtracts right hand operand from left hand operandmark |
The below figure shows the precedence order
The above figure shows the Exponent has high precedence and Addition and Subtraction has lowest precedence.
If you want to change the order of evaluation use parentheses
If operands of expression are of same data type, then resulting value is also that
type. However addition of two ints data type can produce long int.
Python Mixed-Mode Arithmetic
The calculation which entails both integer and floating-point number is called Python mixed-mode arithmetic.
When each operand is of a different type, the resulting value is of the more general type and float type is more general type.
Below figure will clear you doubt.
Python Mixed-Mode conversion
In above example 9/2.0, the less general type int (9) is temporarily and automatically converted into float (9.0) then calculation is performed.
Python Type Conversions
Python type conversion function converts the data type of operand. See the below figure.
In above figure 4.77 converts into 4. If you want convert 4.77 into int use int() function.
If you want to convert into float use float() function.
 Fundamentals of Python: Data Structures by Kenneth Lambert