FUNCTION PARAMETER AND ARGUMENT

Transcription

1 FUNCTION PARAMETER AND ARGUMENT P.POOVIZHI AP-IT SNSCE 1

2 FRAME THE DEFINITION?? 2

3 DEFINITION OF FUNCTION A function is a block of organized, reusable code that is used to perform a single, related action. 3

4 Functions in Python 1.Built-in functions: these functions pre-defined and are always available. 2.Functions defined in modules: these functions are pre-defined in particular modules and can only be used when the corresponding module is imported. 3.User defined functions: these are defined by the programmer. 4

5 Built-in Functions Python documentation lists 80 built-in functions at: abs(), type(), min(), max(), pow(), print(), len(), range() Math functions: cos(x), sqrt(x), factorial(x),ceil(x), floor(x) Type conversion functions: bool(x), float(x), int(x), str(x) Input functions: input(x) Miscellaneous: len(x), id(x) 5

6 Adding New Functions A function definition specifies the name of a new function and the sequence of statements that execute when the function is called. First line of function definition is called header. The rest is called body. Header has to end with colon and the body has to be indented. The statements inside the function do not get executed until the function is called, and the function definition generates no output. Example: def print_lyrics(): header print( I am ok ) print( I am not ok ) def keyword that indicates that this is function definition print_lyrics() - Function name 6

7 Rules for function name Rules for function name is similar to variable names; letters, numbers and punctuation marks are legal, but first character can t be a number. Keyword can t be used as function name. Avoid using variable and function name with same name 7

8 Components of function definition Keyword def marks the start of the function header. A function name to uniquely identify it. Parameters(Arguments) through which values are passed to a function. A colon (:) to mark the end of function header One or more valid python statements that makes function body. An optional return statement to return a value from the function. 8

9 Function Call Once defined, should call the function from other function, program or even the python prompt. 9

10 >>> print_lyrics() Calling the function in python shell Output: I am ok I am not ok 10

11 Repeated calling of the function def repeat_lyrics(): print_lyrics() print_lyrics() >>>repeat_lyrics() Output: I am ok I am not ok I am ok I am not ok 11

12 Definitions and Uses def print_lyrics(): print( I am ok ) print( I am not ok ) def repeat_lyrics(): print_lyrics() print_lyrics() repeat_lyrics() Two function definitions: print_lyrics() repeat_lyrics() 12

13 Advantages of functions Convenient way to divide the code into useful blocks, allowing us to order our code More readable Avoids repetition and makes code reuse Save some time 13

14 Flow of Execution In-order to ensure that a function is defined before its first use, have to know the order in which the statements are executed, which is called flow of execution. Execution always begins at the first statement of the program. Statements are executed one at a time, in order from top to bottom. Function definitions do not alter the flow of execution of the program, but the statements inside the function will be executed only when called. Instead of going to the next statement, the flow jumps to the body of the function, executes all the statements there, then comes back to pick up where it is left off. 14

15 Parameters and Arguments Some inbuilt functions require arguments. Eg. math.sin(x) requires a number as an argument math.pow(x,y) takes two arguments (base and exponent) Inside the function, arguments are assigned to variables called parameters. User defined function Example: def print_twice(bruce): print(bruce) print (bruce) parameter This function assigns the argument to a parameter named bruce. When function is called, it prints the value of the parameter twice. 15

16 Argument and Parameter Difference A parameter is a variable in a function definition. When a method is called, the arguments are the data you pass into the method's parameters. Parameter is variable in the declaration of function. Argument is the actual value of this variable that gets passed to function. 16

17 Calling Function in Python Shell >>>print_twice( Spam ) Spam Spam >>>print_twice(17) >>>print_twice(math.pi) argument Output 17

18 Calling Function in Python Shell >>>print_twice( Spam *4) SpamSpamSpamSpam SpamSpamSpamSpam >>>import math >>>print_twice(math.cos(math.pi)) argument Output 18

19 Variables and Parameters are Local When variables are created inside a function, it is local, which means that is only exists inside the function. Eg: def cat_twice(p1,p2) cat=p1+p2 print(cat_twice(cat)) This function has 2 arguments, concatenates them and print the result twice 19

20 >>> line1= Hi >>>line2= Hello >>>cat(line1,line2) Hi Hello 20

21 Scope and Lifetime of variables Scope of a variable is the portion of a program where the variable is recognized. Parameters and variables defined inside a function is not visible from outside. Hence, they have a local scope. Lifetime of a variable is the period throughout which the variable exits in the memory. The lifetime of variables inside a function is as long as the function executes. They are destroyed once we return from the function. Hence, a function does not remember the value of a variable from its previous calls. 21

22 Scope and Lifetime of variables def my_func(): x = 10 Example print("value inside function:",x) Although they have same names, they are two different variables with different scope. x = 20 my_func() print("value outside function:",x) Output: Value inside function: 10 Value outside function: 20 22

23 Description Here, we can see that the value of x is 20 initially. Even though the function my_func() changed the value of x to 10, it did not effect the value outside the function. This is because the variable x inside the function is different (local to the function) from the one outside. Although they have same names, they are two different variables with different scope. On the other hand, variables outside of the function are visible from inside. They have a global scope. We can read these values from inside the function but cannot change (write) them. In order to modify the value of variables outside the function, they must be declared as global variables using the keyword global. 23

24 ASSESSMENT- IT IS FUNCTION DEFINITION OR CALL?? 24

25 DIFFERENCE BETWEEN PARAMETER AND ARGUMENT?? PARAMETER ARGUMENT 25