Functions_new.pptx

FUNCTIONS
• Some applications contain million lines of code .
• It require a team of programmers to develop such codes and it is
hard to debugging.
• Programs are divided into manageable pieces called program
routines (or simply routines).
• program routines provide the opportunity for code reuse.

MEASURES OF LINES OF PROGRAM CODE

CONTD…
• A ROUTINE is a named group of instructions performing some
task.
• A ROUTINE can be invoked ( called ) as many times as needed in a
given program.
• When a routine terminates, execution automatically returns
to the point from which it was called.
• A function is python’s version of a program routine. Some
functions are designed to return a Value, while others are
designed for other purposes.

CONTD..
• Functions help break our program into smaller and modular
chunks.
• As our program grows larger and larger, functions make it more
organized and manageable.
• TYPES OF FUNCTIONS:
• BUILT-IN FUNCTIONS
• USER DEFINED FUNCTIONS

TYPES OF FUNCTIONS
• BUILT-IN FUNCTIONS:The python interpreter has a
number of functions that are always available for
use.
• These functions are called built-in functions.
• Example: print() function prints the given object to
the standard output device (screen) or to the text
stream file
• USER DEFINED FUNCTIONS:Functions that we define
ourselves to do certain specific task are referred as
user-defined functions.

CONTINUE….
• LEN:RETURN THE LENGTH (THE NUMBER OF ITEMS) OF AN
OBJECT. THE ARGUMENT MAY BE A SEQUENCE (SUCH AS A
STRING, BYTES, TUPLE, LIST, OR RANGE) OR A COLLECTION
(SUCH AS A DICTIONARY, SET, OR FROZEN SET).

CONTINUE….
• ROUND:RETURN NUMBER ROUNDED TO NDIGITS PRECISION
AFTER THE DECIMAL POINT. IF NDIGITS IS OMITTED OR
IS NONE, IT RETURNS THE NEAREST INTEGER TO ITS INPUT.
• SORTED:RETURN A NEW SORTED LIST FROM THE ITEMS IN
ITERABLE
• POWER:THE POW() METHOD RETURNS X TO THE POWER OF Y
• SUM:SUM(ITERABLE) SUMS THE NUMERIC VALUES IN AN
ITERABLE SUCH AS A LIST, TUPLE, OR SET.
SUM(ITERABLE) DOES NOT WORK WITH STRINGS BECAUSE YOU
CAN'T DO MATH ON STRINGS (WHEN YOU ADD TWO STRINGS
YOU ARE REALLY USING AN OPERATION CALLED
CONCATENATION).

CONTINUE…….
• HELP:THE HELP() FUNCTION IS YOUR NEW BEST FRIEND. INVOKE
THE BUILT-IN HELP SYSTEM ON ANY OBJECT AND IT WILL
RETURN USAGE INFORMATION ON THE OBJECT.

FUNCTION CALL
• When you define a function, you specify the name and the
sequence of
Statements.
• Later, you can “call” the function by name.
• Ex: >>> type(32)
<type 'int’>
• The name of the function is type. The expression in parentheses is
called the argument of the function.
• The result, for this function, is the type of the argument.

TYPE CONVERSION FUNCTIONS
• Python provides built-in functions that convert values from one type to
another.
• The int Function takes any value and converts it to an integer, if it can,
or complains otherwise.
• Ex: >>>int(‘32’)
32
>>>int(‘Hello’)
Value Error: invalid literal for int(): Hello
>>>int(3.9)
3

CONTD..
• float converts integers and strings to floating-point numbers.
• str converts its argument to a string.
• Ex:
>>> FLOAT(32)
32.0
>>> FLOAT('3.14159')
3.14159
>>> STR(32)
'32'
>>> STR(3.14159)
'3.14159'

MATH FUNCTIONS
• Python has a math module that provides most of the familiar
mathematical functions.
• A module is a file that contains a collection of related functions.
• Before we can use the module, we have to import it:
>>> import math
• Ex:
>>> ratio = signal_power / noise_power
>>> decibels = 10 * math.log10(ratio)
>>> radians = 0.7
>>> height = math. sin(radians)

COMPOSITION
• One of the most useful features of programming languages is
their ability to take small Building blocks and compose them.
• For example, the argument of a function can be any Kind of
expression, including arithmetic operators and even function calls:
• Ex:
>>>x = math.sin(degrees / 360.0 * 2 * math.pi)
>>>x = math.exp(math.log(x+1))

ADDING NEW FUNCTIONS
• So far, we have only been using the functions that come with python, but
it is also possible to add new functions.
• A function definition specifies the name of a new function and the
sequence of statements that execute when the function is called.
• Ex:
def print_lyrics():
print "i'm a lumberjack, and i'm okay."
print "i sleep all night and i work all day."
Empty paranthesis indicates no
arguments
Name of
function
Keyword to indicate function
definition

CONTD..
• The first line of the function definition is called the header; the
rest is called the body.
• The header has to end with a colon and the body has to be
indented.
• By convention, the Indentation is always four spaces .
• The body can contain any number of Statements.
• To end the function, you have to enter an empty line in interactive
mode.
• The syntax for calling the new function is the same as for built-in
functions:
>>> print_lyrics()
I'm a lumberjack, and I'm okay.

CONTD..
• Once you have defined a function, you can use it inside another
function.
• For example, to repeat the previous refrain, we could write a
function called repeat_lyrics:
• >>>def repeat_lyrics():
print_lyrics()
print_lyrics()

ADVANTAGES OF USER DEFINED
FUNCTIONS
• User-defined functions help to decompose a large
program into small segments which makes program
easy to understand, maintain and debug.
• If repeated code occurs in a program,function can
be used to include those codes and execute when
needed by calling that function.
• Programmers working on large project can divide
the workload by making different functions.

DEFINITIONS AND USES
>>>def print_lyrics():
print "i'm a lumberjack, and i'm okay."
print "i sleep all night and i work all day."
>>>def repeat_lyrics():
print_lyrics()
print_lyrics()
>>>repeat_lyrics()
i'm a lumberjack, and i'm okay.
i sleep all night and i work all day.
i'm a lumberjack, and i'm okay.
i sleep all night and i work all day.

CONTD..
• Function definitions get executed just like other statements, but
the effect is to create function objects.
• The statements inside the function do not get executed until the
function is called, and the function definition generates no output.
• The function definition has to be executed before the first time it
is called.
• Try the following
• Move the last line of the program to the top.
• Move the definition of print_lyrics after the definition of
repeat_lyrics.

FLOW OF EXECUTION
• Execution always begins at the first statement of the program.
• Function definitions do not alter the flow of execution of the
program, but remember that statements inside the function are
not executed until the function is called.
• During the function call the flow jumps to the body of the
function, executes all the statements there, and then comes back
to pick up where it left off.
• Python is good at keeping track of where it is.
• When it gets to the end of the program, it terminates

PARAMETERS AND ARGUMENTS
• Some of the functions takes arguments.
• Ex:
def print_twice(bruce):
print bruce
print bruce
• This function assigns the argument to a parameter named bruce.
• When the function is called, it prints the value of the parameter
(whatever it is) twice.

ARGUMENTS IN FUNCTIONS
• You can call a function by using the following types
of formal arguments:
1.Required arguments
2. Keyword arguments
3.Default arguments
4.Variable-length arguments

REQUIRED ARGUMENTS
• Required arguments are the arguments passed to a
function in correct positional order.
• Here, the number of arguments in the function call
should match exactly with the function definition.
• To call the function printme(), you definitely need to
pass one argument, otherwise it gives a syntax error
as follows

KEYWORD ARGUMENTS
• Keyword arguments are related to the function calls. When you use
keyword arguments in a function call, the caller identifies the
arguments by the parameter name.
• This allows you to skip arguments or place them out of order
because the python interpreter is able to use the keywords
provided to match the values with parameters.

CONTINUE….
 You can also make keyword calls to the
printme() function in the following ways –

CONTINUE…
• The following example gives more clear picture. Note that the
order of parameters does not matter

DEFAULT ARGUMENTS
• A default argument is an argument that assumes a
default value if a value is not provided in the
function call for that argument.
• The following example gives an idea on default
arguments, it prints default age if it is not passed

VARIABLE LENGTH
ARGUMENTS
• You may need to process a function for more arguments than you
specified while defining the function
• These arguments are called variable-length arguments and are
not named in the function definition, unlike required and default
arguments.

CONTINUE….
• SYNTAX FOR A FUNCTION WITH NON-KEYWORD VARIABLE
ARGUMENTS
An asterisk (*) is placed before the variable name
that holds the values of all no keyword variable
arguments.
This tuple remains empty if no additional
arguments are specified during the function call

CONTINUE…..
>>> printinfo(10)
ouptput is:
10
>>> printinfo(10,20,30)
ouptput is:
10
20
30

VARIABLES AND PARAMETERS ARE LOCAL
• When you create a variable inside a function, it is local, which
means that it only exists inside the function.

STACK DIAGRAMS
• To keep track of which variables can be used where, it is
sometimes useful to draw a stack diagram.
• Stack diagrams show the value of each variable, but they also
show the function each variable belongs to.
• Each function is represented by a frame.
• A frame is a box with the name of a function beside it and the
parameters and variables of the function inside it.
• The frames are arranged in a stack that indicates which function
called which, and so on.

CONTD..
• In the above example, print_twice was called by cat_twice, and
cat_twice was called by __main__, which is a special name for the
topmost frame.
• When you create a variable outside of any function, it belongs to
__main__.
• If an error occurs during a function call, python prints the name of
the function, and the name of the function that called it, and the
name of the function that called that, all the way back to __main__.
• Ex: If you try to access cat from within print_twice, you get a Name Error:

CONTD..
• This list of functions is called a traceback.
• It tells you what program file the error occurred in, and what line,
and what functions were executing at the time. It also shows the
line of code that caused the error.
• The order is the same as the order of the frames in the stack
diagram.

FRUITFUL FUNCTIONS AND VOID FUNCTIONS
• Some of the functions we are using yield results.bhey are called as
fruitful functions.
• If fruitful functions are running in interactive mode python will
display the result but in script mode the retun value will be lost
• Ex: math.sqrt(5).
• Whereas other functions, perform an action but don’t return a
value. They are called void functions.
• If you try to assign the result to a variable, you get a special value
called None.
• Ex: result=print_twice

WHY FUNCTIONS?
Gives you an opportunity to name a group of statements, which
makes your program easier to read and debug.
Functions can make a program smaller by eliminating repetitive
code.
Allows you to debug the parts one at a time and then assemble
them into a working whole.
Well-designed functions are often useful for many programs.

Functions_new.pptx

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