4. Variables

4.   Variables in python

ü  What is variable?

ü  Properties of variable

ü  Creating variable

ü  Invalid cases for variables

ü  Multiple variables in single line

ü  Single value for multiple variables

ü  Variable re-initialization

ü  Programs

4. Variables

4. 1 Variable

ü  A variable is a,

o   name.

o   refers to a value.

o   holds the data

o   name of the memory location.

Program      printing variable Name          demo1.py emp_id=101 print(emp_id) Output                   101

4.2 Properties of variable

ü  Every variable has a,

o   Type

o   Value

o   Scope

o   Location

o   Life time

4.3 Creating variable

ü  In python, to create a variable we need to specify,

o   The name of the variable

o   Assign a value to name of the variable.

Syntax                   name_of_the_variable = value

Program       creating a variable Name          demo2.py                   age=16                   print(age)          output                            16

Program       creating a variable and displaying with a meaningful text message Name          demo3.py                   age=16                   print(“My age is sweet: ”, age)          output                            My age is sweet: 16

Make a Note

ü  We can print meaningful text message along with variable for better understanding

o   Text message we should keep in within double quotes.

o   Text message and variable name should be separated by comma symbol.

Above example:

                  age    ----->          name of the variable

                  16      ----->          value or literal

4. 4 Invalid cases for variables

1.   While defining a variable,

o   Variable name should be written in the left-hand side.

o   The value should be written in the right-hand side

o   Otherwise, we will get a syntax error.

Program       Creating variable in the wrong direction Name          demo4.py                   10 = emp_id                   print(emp_id) Error                   SyntaxError: can't assign to literal

2.   variables names,

o   should not give as keywords names, otherwise, we will get error

Program      printing a variable name which having digits in the name Name          demo5.py if = 10 print(if) Error                   SyntaxError: invalid syntax

4.5 Multiple variables in single line

1.   We can assign multiple variables to multiple values in a single one line.

2.   Rule

a.   While defining there should be the same number on the left and right-hand sides. Otherwise, we will get an error.

Program       assign multiple variables in single line Name          demo6.py a, b, c = 1, 2, 3 print(a, b, c) output                   1 2 3

Program       Invalid case: assign multiple variables which are not matched names and values Name          demo7.py a, b, c = 1, 2 print(a, b, c) Error                   ValueError: not enough values to unpack (expected 3, got 2)

Program       Invalid case: assign multiple variables which are not matched names and values Name          demo8.py a, b = 1, 2, 3 print(a, b, c) Error                   ValueError: too many values to unpack (expected 2)

4.6 Single value for multiple variables

ü  We can assign a single value to several variables simultaneously.

Program       Assign single value to multiple variables Name          demo9.py a = b = c = 1 print(a, b, c)         Output                 1 1 1

4.7 Variable re-initialization

ü  We can reinitialize variable values.

ü  Re-initialize

o   In variable re-initialization, old values will be replaced or overridden with new values.

Program       Re-initialising variable Name          demo10.py a =10 print(“first time value:”, a) a = 20 print(“variable is re-initialized, now the value is:”, a)      a = 30 print(“again the variable is re-initialized, now the value is:”, a) Output first time value : 10 variable is re-initialized, now the value is: 20 again the variable is re-initialized, now the value is: 30