541   True

   541   True

   542   >>> f and t

   542   >>> f and t

   543   False

   543   False

   544 

   544 

   545 The **while** loop

   545 The **while** loop

   547 

   548 

   548 The Python **while** loop is similar to the C/C++ while loop. The syntax is as

   549 The Python **while** loop is similar to the C/C++ while loop. The syntax is as

   549 follows:

   550 follows:

   550 

   551 

   551 ::

   552 ::

   570     3

   571     3

   571     4

   572     4

   572     5

   573     5

   573 

   574 

   574 The **if** conditional

   575 The **if** conditional

   576 

   577 

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

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

   579 block are executed.

   580 block are executed.

   580 

   581 

   610          print n," is positive"

   611          print n," is positive"

   611          else:

   612          else:

   612          print n, " is 0"

   613          print n, " is 0"

   613 

   614 

   614 **raw_input()**

   615 **raw_input()**

   616 

   617 

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

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

   683 

   684 

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

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

   686 

   687 

   687 **int()** method

   688 **int()** method

   689 

   690 

   690 Generally for computing purposes, the data used is not strings or raw data but 

   691 Generally for computing purposes, the data used is not strings or raw data but 

   691 on integers, floats and similar mathematical data structures. The data obtained

   692 on integers, floats and similar mathematical data structures. The data obtained

   692 from **raw_input()** is raw data in the form of strings. In order to obtain integers

   693 from **raw_input()** is raw data in the form of strings. In order to obtain integers

   693 from strings we use the method **int()**. 

   694 from strings we use the method **int()**. 

   713   'Guido Van Rossum'

   714   'Guido Van Rossum'

   714   >>> numvar = int(stringvar)

   715   >>> numvar = int(stringvar)

   715 

   716 

   716 

   717 

   717 Functions in Python: **def**

   718 Functions in Python: **def**

   719 

   720 

   720 *Functions* allow us to enclose a set of statements and call the function again

   721 *Functions* allow us to enclose a set of statements and call the function again

   721 and again instead of repeating the group of statements everytime. Functions also

   722 and again instead of repeating the group of statements everytime. Functions also

   722 allow us to isolate a piece of code from all the other code and provides the

   723 allow us to isolate a piece of code from all the other code and provides the

   723 convenience of not polluting the global variables.

   724 convenience of not polluting the global variables.

   807 

   808 

   808   >>> name = ['Mr.', 'Steve', 'Gosling']

   809   >>> name = ['Mr.', 'Steve', 'Gosling']

   809   >>> can_change(name)

   810   >>> can_change(name)

   810   >>> name

   811   >>> name

   811   ['Mr.', 'James', 'Gosling']

   812   ['Mr.', 'James', 'Gosling']

   813 If nothing is returned by the function explicitly, Python takes care to return

   813 If nothing is returned by the function explicitly, Python takes care to return

   814 None when the funnction is called.

   814 None when the funnction is called.

   815 

   815 

   816 Default Arguments

   816 Default Arguments

   817 -----------------

   817 -----------------