Python – Variables, Values, Types & Keywords.

Variables, Values, Types & Keywords in python

Values

A value can be a number, letter, word etc. It can be of any data type like int, string, float etc.

eg: 100,20.20,”itvoyagers”

>>> a="itvoyagers"
>>> a
'itvoyagers'
>>> b=5
>>> b
5
>>> c=50.5
>>> c
50.5
>>> 

NOTE : In Python it is not necessary to mention the datatype before defining variable. Value assigned to variable denotes the datatype of that variable

Type function

If you want to know the type of value assigned to a variable , use type statement.

Example: type(a),type(b),type(3),type(“3”) etc

Variables

Variables are pointers pointing to a memory location containing value or data. Depending on the data type of value assigned, the interpreter reserves the memory. In python variable declaration is not required. To assign a value to the variable equal to (=) sign is used. Value is present on left side of “=” sign and variable to the right.

eg : p=100

Here , id(p) will show the memory location of data

type(p) will show the datatype of data at which p is pointing

p=q will create a new pointer “q” that will point to the same memory location as that of “p”

Multiple assignments

You can assign same value to many/different variables or different values to different variables in single statement. Also you can use same variable to re-assign different value after using or deleting previous value.

#same value to multiple variables
>>> f=o=g=100
>>> f
100
>>> o
100
>>> g
100
#different values to different variables
>>> m,i,b="itvoyagers",1,1.1 
>>> m
'itvoyagers'
>>> i
1
>>> b
1.1
#reusing same variable to assign new value
>>> i="India"
>>> i
'India'
>>> i=1947
>>> i
1947

#Program to swap values
x,y=10,500  #step 1
print("before swap")
print("x is",x)
print("y is",y)
y,x=x,y # step 2
print("after swap")
print("x is",x)
print("y is",y)
NOTE: In above example step 2 is swapping values.Python enables swapping in single line

Rules to define variables name

1. Variables are case sensitive

2. Variables can be alphanumeric

3. Variable name should begin with letters (a-z,A-Z) or Underscore (_)

4. Variable name can never begin with number

5. Keywords can never be used as variable name

6. Variables can be of any length

7. No spaces are allowed in variable name

8. No special symbols are allowed apart from underscore(_)

9. No need to give data type name before defining variable

#few examples of rules
#Variables are case sensitive
>>> a=5
>>> A
Traceback (most recent call last):
  File "", line 1, in 
    A
NameError: name 'A' is not defined
>>> 
#Variable name can never begin with number
1A="HI"
SyntaxError: invalid syntax
>>> 
#Keywords can never be used as variable name
>>> if=5
SyntaxError: invalid syntax
# No spaces are allowed in variable name
>>> first name="pk"
SyntaxError: invalid syntax

Keywords

Keywords are reserved words and cannot be used as variable names.

There are 33 keywords in python.

Python Keywords

anddefforisreturnFalse
asdelfromlambdatryNone
assertelifglobalnotwhile
breakelseiforwith
classexceptimportpassyield
continuefinallyinraiseTrue

NOTE : All keywords are in lower case except True, False and None have first letter in uppercase

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