Python Variables & User Input

Python Variables & User Input

There are many python detail tutorials available all over the internet. The purpose of these tutorial is to quickly go thru the basic variables available and user inputs in Python. Always remember that python is case sensitive language, therefore variable names num1, Num1 & NUM1 will be treated different variables.

• Variables in Python
  • Local Variable
  • Global Variable
• Datatypes in Python
  • Numeric
  • Boolean
  • String
• User Input in Python
• Data structure in Python
• Delete variable in Python

➠ Variables in Python: In python, users don't have to specifically declare variables before assigning values to it. Variable name can only start with either an alphabet or an underscore(_). Variables can be of 2 type with respect to Functions:

• Local Variables: Local variables are those variable which can be accessed only within the function block where those are defined. By default all the function variables are local variables and can't be accessed outside of function.

  
  x=10
  def variableTest(x):
      x = x +1    #x is the local variable  
      print("Value inside function x= "+str(x))
  
  >>> variableTest(x)
  Output:  Value inside function x= 11
  
  >>> print("Value outside function x= "+str(x))
  Output:  Value outside function x= 10
  

  
  
• Global Variables: Global variables are those variable which can accessed anywhere in the code but for using global variable within function, it need to be declared as global in function definition.

  
  x=10
  def variableTest(num):
      global x    #x is declared Global variable
      x = x +1
      print("Value inside function x= "+str(x))
  
  >>> variableTest(x)
  Output:  Value inside function x= 11
  
  >>> print("Value outside function x= "+str(x))
  Output:  Value outside function x= 11
  

➠ Datatypes in Python: In python, users don't have to specifically declare types of the variable before assigning values to it.

• Numeric: Python will define the type of variable appropriately. As it can be seen in the examples below, python has defined number as 'Integer' when it was whole number but 'float' when it was in decimal.

  
  >>> num1=11
  >>> type(num1)
  Output: <type 'int'>
  
  >>> print(num1)
  Output:  11
  
  >>> num2=13
  >>> num1+num2
  Output:  24
  
  
  >>> num4=2.5
  >>> type(num4)
  Output:  <type 'float'>
  
  
  >>> num5=num1 + num4
  >>> num5
  Output:  13.5
  
  
  >>> type(num5)
  Output:  <type 'float'>
  

  
  
• Boolean: There are only 2 possible values: True and False. These boolean values are case sensitive, as you can see in the 3rd example below

  
  >>> boolTest=False
  >>> type(boolTest)
  Output:  <type 'bool'>
  
  
  >>> boolTest2=True
  >>> type(boolTest2)
  Output:  <type 'bool'>
  
  
  >>> boolTest3=TRUE
  Output:  
  Traceback (most recent call last):
    File "", line 1, in 
  NameError: name 'TRUE' is not defined
  

  
  
• String: Python provides a way to slice string data at each character level as it is stored as array.
  • Below image will show pictorial representation of string in Python.
  • There are many string function directly available in python and these will be covered in other tutorial.
  • Each character can be accessed by using its position.
  • Zero represents first position and -1 represent last character of the string.
  • User can extract part of the string by specifying start position & end position.
  • User can extract pattern from the string by specifying start position, end position and gap(number of character to skip).
  • Two strings can be appended using plus(+) sign.
  • When user tries to access index equal to or bigger than length of string then it will with error 'string index out of range'
    
  • Some of the examples for the points discussed above
    

    
    >>> str1='DBMS'
    >>> type(str1)
    Output:  <type 'str'>
    
    
    >>> str2='TUTORIALS'
    >>> print(str2)
    Output:  TUTORIALS
    
    
    >>> str3 = str1+' '+str2
    >>> print(str3)
    Output:  DBMS TUTORIALS
    
    
    >>> print(str3[0]+str3[-1])
    Output:  DS
    
    
    >>> print(str3[6:-1]) #Extracting part of the string
    Output:  UTORIAL
    
    
    >>> print(str3[1:-1:2]) #Extracting pattern from the string
    Output:  BSTTRA
    
    
    >>> print(str3[-1::-1]) #Reverse String
    Output:  SLAIROTUT SMBD
    
    
    >>> print(str3[14])
    Output:  Traceback (most recent call last):
      File "", line 1, in 
    IndexError: string index out of range
    

  • Multiline String: Users can define multiline strings using triple quotes.

    
    >>> str4='''This is multiline
    string'''
    
    >>> print(str4)
    Output: 
    This is multiline
    string
    

  
  

➠ User Input in Python: Python supports taking input from users and there are 2 function to use this feature, raw_input(deprecated) & input.

• raw_input(): raw_input was introduced in python 2 and is deprecated, may not work in python v3.0 onwards

  
  >>> input_var = raw_input()
  Input: Dbmstutorials
  
  
  >>> print(input_var)
  Output: Dbmstutorials
  

• input(): Python encourage to use 'input' function instead of 'raw_input' becauese 'raw_input' is deprecated. 'input' function was more strict in terms of passing string as user input in Python version 2.7, user had to specifically provide quotes around the string for Python to treat it as String otherwise it will assume it as variable and throw error 'user_input_value is not defined'.

  
  >>> input_var1 = input()
  Input: 3
  
  >>> print(input_var1)
  Output: 3
  
  
  >>> input_var=input()    #This will only fail in lower version and not in Python 3
  Input: Dbmstutorials
  Output: Traceback (most recent call last):
    File "", line 1, in 
    File "", line 1, in 
  NameError: name 'Dbmstutorials' is not defined
  
  
  >>> input_var1 = input()
  Input: 'Dbmstutorials'
  
  >>> print(input_var1)
  Output: Dbmstutorials
  
  
  
  >>> input_var=input()    #This will work fine in Python 3
  Input: Dbmstutorials
  
  >>> print(input_var)
  Output: Dbmstutorials
  
  
  
  >>> input_var1=input()    #This will work fine in Python 3 but quote will be the first character in the string.
  Input: 'Dbmstutorials'
  
  >>> print(input_var)
  Output: 'Dbmstutorials'
  
  >>> print(input_var1[0])
  Output: '(single Quote)
  

➠ Data Structures in Python: Primarily there are 4 types of data structures in python. Some of characteristics of all the data structures are listed below:

• List, Set and Dictionary data structures are mutable but Tuple data structure is not mutable(i.e. unchangeable).
• All these data structures can be empty or made up of either homogenous items(same datatype) or heterogenous items(same/different datatype and data structures).
• All these data structures are iterable.
• There are many functions/methods directly available for data structures in python and these will be covered in other tutorial.

• List: Here are some examples of defining List and few basic operations on List data structure.

  
  >>> alist = [1, 'a',{1,'a'}]
  >>> type(alist)
  
  Output: <type 'list'>
  
  
  >>> alist=[1, 'a','b']
  >>> alist.extend('c')
  >>> alist
  Output: [1, 'a', 'b', 'c']
  
  
  >>> alist.pop()
  Output: 'c'
  
  
  >>> for i in alist:
  ...     print(i)
  Output: 
  1
  a
  b
  

• Tuple: Here are some examples of defining tuple and iteration on tuple data structure.

  
  >>> atuple = (2,3,1,'a')
  >>> type(atuple)
  Output: <type 'tuple'>
  
  
  >>> for i in atuple:
  ...     print(i)
  Output: 
  2
  3
  1
  a
  

• Set: Here are some examples of defining Set and few basic operations on Set data structure.

  
  >>> aset = {2,3,4,5,2,4,'a'}
  >>> type(aset)
  Output: <type 'set'>
  
  
  >>> aset.add('b')
  >>> aset
  Output: set(['a', 2, 3, 4, 5, 'b'])
  
  
  >>> aset.pop()
  Output: 'a'
  
  
  >>> print(aset)
  Output: set([2, 3, 4, 5, 'b'])
  
  
  set([2, 3, 4, 5, 'b'])
  >>> for i in aset:
  ...     print(i)
  Output: 
  2
  3
  4
  5
  b
  

• Dictionary: Here are some examples of defining Dictionary and few basic operations on Dictionary data structure.

  
  >>> adict = {"a":"Python",1:"Java"}
  >>> type(adict)
  Output: <type 'dict'>
  
  
  >>> adict.update({'4':'Oracle'})
  >>> adict
  Output: {'a': 'Python', 1: 'Java', '4': 'Oracle'}
  
  
  >>> adict.pop("a")
  Output: 'Python'
  
  
  >>> print(adict)
  Output: {1: 'Java', '4': 'Oracle'}
  
  
  >>> for key in (adict):
  ...     print('key='+str(key)+' val='+str(adict[key]))
  Output: 
  key=1 val=Java
  key=4 val=Oracle
  

➠ Deleting a variable: Existing variables can be deleted in Python using 'del' command.

• 
  >>> str3
  Output:  'DBMS TUTORIALS'
  
  >>> del str3
  >>> str3
  Output:  Traceback (most recent call last):
    File "", line 1, in 
  NameError: name 'str3' is not defined