Variables
Variables
The concept of variable is similar to as in other programming languages. A variable is a name which can be used as a reference to a value. A variable can be treated as some memory location where it can store some data or any value assigned to it. When a value is assigned to a variable it stores in some memory location.
Let’s have a look on variables in brief:
Declaration of variables in different formats
| >>> x=16 # integer variable
>>> y=13.26 #float variable >>> z=”Flipkart” # string variable |
To print the above examples use print( )
| >>> print(x)
16 >>> print(y) 16.26 >>> print(z) Flipkart |
You can also check the type of the variable as shown in below.
| >>> type(x)
<class ‘int’> >>> type(z) <class ‘str’> |
We can also re-declare the variable even after once it is already declared. It is shown in below:
| >>> x=4
>>> print(x) 4 >>> x=”my_variable” >>> print(x) my_variable |
Note: After re-declaring a variable, it will print the recently assigned value.
You can also delete a variable by using ‘del’ command.
| >>> var=123
>>> var 123 >>> del var >>> var Traceback (most recent call last): File “<pyshell#10>”, line 1, in <module> var NameError: name ‘var’ is not defined |
We can increase the value of specific variable and it shown in below
| >>> a=1
>>> b=a+2 >>> b 3
>>> print(b) 3 |
Note: The variable type changes every time during execution. It is shown in the following example.
| >>> k=26 #int variable
>>> k=26+1.4 #addition of int and float but resultant is float >>> k 27.4 >>> k=”Sixty” #and now it is string >>> k ‘Sixty’ |
If you want to integrate both the text and variable, just look at the below example
| >>> var=”interesting”
>>> print(“Python is”+var) Python is interesting |
If you want to integrate a variable with the other variable then:
| >>> s=”Hello” #in case of strings
>>> t=”Sudhakar” >>> u=s+t >>> print(u) HelloSudhakar
>>> print(s+t) HelloSudhakar >>> i=3 #in case of integers >>> j=5 >>> print(i+j) 8 |
id( )
As we discussed earlier the variable has some memory location. So to find the location of specific variable we use identity function (id( )).
Ex:
| >>> a=13
>>> id(a) 1492447408 #Memory location of variable ‘a’ >>> a=b >>> id(a),id(b) (1492447088, 1492447088) >>> >>> b=14 >>> id(a),id(b) (1492447088, 1492447440) |
Multiple assignment of variables
We can assign a value to the multi variables at a time.
Ex:
| p=q=r=6
a,b,c=2,1.11,”One” |
Naming Conventions:
Do’s and Don’ts of variables
| Do’s |
Don’ts |
| 1.Must start with a letter or an underscore (‘_’).
Ex: _python or python_. 2.It must include characters from (a-z/A-Z/0-9) and ‘_’. Ex: abc12, 5A2, pr_ogra_mmin_g. 3.Variables are case-sensitive. Ex: Snow,snow,SNOW are considered as three different variables. 4. An identifier consists of letters and digits. 5. In case of identifiers special ‘_'(underscore) can be used. 6. Examples of valid declaration of identifiers in Python are : BeHappy,mychoice,Twoapples, The_Movie
|
1. Do not start with number. Ex: 6=a. 2. Avoid the usage of both lowercase and uppercase of letter ‘i’ and uppercase letter ‘o’. because ‘i’ and ‘o’ look like 1 and 0. 3. A variable name cannot match with the existing reserve words/keywords. Ex:as=9. 4. An identifier cannot begin with ‘_’ and a digit. 5. Spaces and quotes are not considered to be part of an identifier. 6. Examples of invalid declaration of identifiers in Python: a.’BeHappy’ — quotes are ignored b. my choice — spaces are ignored c. 2apples — we cannot start with a digit. d. _TheMovie — we cannot start with ‘_’. |
