562   

   562 

   563   

   563     >>> x = 1  

   564     >>> while x <= 5:

   565     ...   print x

   566     ...   x += 1

   567     ... 

   568     1

   569     2

   570     3

   571     4

   572     5

   573 

   574 The **if** conditional

   575 ~~~~~~~~~~~~~~~~~~~~~~

   576 

   577 The Python **if** block provides the conditional execution of statements. 

   578 If the condition evaluates as true the block of statements defined under the if 

   579 block are executed.

   580 

   581 If the first block is not executed on account of the condition not being satisfied,

   582 the set of statements in the **else** block are executed.

   583 

   584 The **elif** block provides the functionality of evaluation of multiple conditions

   585 as shown in the example.

   586 

   587 The syntax is as follows:

   588 

   589 ::

   590 

   591   if condition :

   592       statement_1

   593       statement_2

   594 

   595   elif condition:

   596       statement_3

   597       statement_4

   598   else:

   599       statement_5

   600       statement_6

   601 

   602 Let us look at an example:

   603 

   604 ::

   605   

   606    >>> n = raw_input("Input a number:")

   607    >>> if n < 0:

   608          print n," is negative"

   609          elif n > 0:

   610          print n," is positive"

   611          else:

   612          print n, " is 0"

   613 

   614 **raw_input()**

   615 ~~~~~~~~~~~~~~~

   616 

   617 In the previous example we saw the call to the raw_input() subroutine. 

   618 The **raw_input()** method is used to take user inputs through the console.

   619 Unlike **input()** which assumes the data entered by the user as a standard python

   620 expression, **raw_input()** treats all the input data as raw data and converts

   621 everything into a string. To illustrate this let us look at an example.

   622 

   623 ::

   624 

   625   >>> input("Enter a number thats a palindrome:")

   626   Enter a number thats a palindrome:121

   627   121

   628 

   629   >>> input("Enter your name:")

   630   Enter your name:PythonFreak

   631   Traceback (most recent call last):

   632     File "<stdin>", line 1, in <module>

   633     File "<string>", line 1, in <module>

   634   NameError: name 'PythonFreak' is not defined

   635 

   636 As shown above the **input()** assumes that the data entered is a valid Python

   637 expression. In the first call it prompts for an integer input and when entered

   638 it accepts the integer as an integer, whereas in the second call, when the string

   639 is entered without the quotes, **input()** assumes that the entered data is a valid

   640 Python expression and hence it raises and exception saying PythonFreak is not 

   641 defined.

   642 

   643 ::

   644 

   645   >>> input("Enter your name:")

   646   Enter your name:'PythonFreak'

   647   'PythonFreak'

   648   >>> 

   649 

   650 Here the name is accepted because its entered as a string (within quotes). But

   651 its unreasonable to go on using quotes each time a string is entered. Hence the

   652 alternative is to use **raw_input()**.

   653 

   654 Let us now look at how **raw_input()** operates with an example.

   655 

   656 ::

   657 

   658   >>> raw_input("Enter your name:")

   659   Enter your name:PythonFreak

   660   'PythonFreak'

   661 

   662 Observe that the **raw_input()** is converting it into a string all by itself.

   663 

   664 ::

   665 

   666   >>> pal = raw_input("Enter a number thats a palindrome:")

   667   Enter a number thats a palindrome:121

   668   '121'

   669 

   670 Observe that **raw_input()** is converting the integer 121 also to a string as 

   671 '121'. Let us look at another example:

   672 

   673 ::

   674   

   675   >>> pal = raw_input("Enter a number thats a palindrome:")

   676   Enter a number thats a palindrome:121

   677   >>> pal + 2

   678   Traceback (most recent call last):

   679     File "<stdin>", line 1, in <module>

   680   TypeError: cannot concatenate 'str' and 'int' objects

   681   >>> pal

   682   '121'

   683 

   684 Observe here that the variable *pal* is a string and hence integer operations

   685 cannot be performed on it. Hence the exception is raised.

   686 

   687 **int()** method

   688 ~~~~~~~~~~~~~~~~

   689 

   690 Generally for computing purposes 

   691 

   692 Let us look at an example.