A function is a set of statements that take inputs, do some specific computation and produces output. The idea is to put some commonly or repeatedly done task together and make a function, so that instead of writing the same code again and again for different inputs, we can call the function.
Python provides built-in functions like print(), etc. but we can also create your own functions. These functions are called user-defined functions.
# A simple Python function to check # whether x is even or odd def evenOdd( x ): if (x % 2 = = 0 ): print "even" else : print "odd" # Driver code evenOdd( 2 ) evenOdd( 3 ) |
even odd
Pass by Reference or pass by value?
One important thing to note is, in Python every variable name is a reference. When we pass a variable to a function, a new reference to the object is created. Parameter passing in Python is same as reference passing in Java.
# Here x is a new reference to same list lst def myFun(x): x[ 0 ] = 20 # Driver Code (Note that lst is modified # after function call. lst = [ 10 , 11 , 12 , 13 , 14 , 15 ] myFun(lst); print (lst) |
[20, 11, 12, 13, 14, 15]
When we pass a reference and change the received reference to something else, the connection between passed and received parameter is broken. For example, consider below program.
def myFun(x): # After below line link of x with previous # object gets broken. A new object is assigned # to x. x = [ 20 , 30 , 40 ] # Driver Code (Note that lst is not modified # after function call. lst = [ 10 , 11 , 12 , 13 , 14 , 15 ] myFun(lst); print (lst) |
[10, 11, 12, 13, 14, 15]
Another example to demonstrate that reference link is broken if we assign a new value (inside the function).
def myFun(x): # After below line link of x with previous # object gets broken. A new object is assigned # to x. x = 20 # Driver Code (Note that lst is not modified # after function call. x = 10 myFun(x); print (x) |
10
Exercise: Try to guess the output of following code.
def swap(x, y): temp = x; x = y; y = temp; # Driver code x = 2 y = 3 swap(x, y) print (x) print (y) |
2 3
Default arguments:
A default argument is a parameter that assumes a default value if a value is not provided in the function call for that argument.The following example illustrates Default arguments.
# Python program to demonstrate # default arguments def myFun(x, y = 50 ): print ( "x: " , x) print ( "y: " , y) # Driver code (We call myFun() with only # argument) myFun( 10 ) |
('x: ', 10) ('y: ', 50)
Like C++ default arguments, any number of arguments in a function can have a default value. But once we have a default argument, all the arguments to its right must also have default values.
Keyword arguments:
The idea is to allow caller to specify argument name with values so that caller does not need to remember order of parameters.
# Python program to demonstrate Keyword Arguments def student(firstname, lastname): print (firstname, lastname) # Keyword arguments student(firstname = 'Geeks' , lastname = 'Practice' ) student(lastname = 'Practice' , firstname = 'Geeks' ) |
('Geeks', 'Practice') ('Geeks', 'Practice')
Variable length arguments:
We can have both normal and keyword variable number of arguments. Please see this for details.
# Python program to illustrate # *args for variable number of arguments def myFun( * argv): for arg in argv: print (arg) myFun( 'Hello' , 'Welcome' , 'to' , 'GeeksforGeeks' ) |
Hello Welcome to GeeksforGeeks
# Python program to illustrate # *kargs for variable number of keyword arguments def myFun( * * kwargs): for key, value in kwargs.items(): print ( "%s == %s" % (key, value)) # Driver code myFun(first = 'Geeks' , mid = 'for' , last = 'Geeks' ) |
last == Geeks mid == for first == Geeks
Anonymous functions: In Python, anonymous function means that a function is without a name. As we already know that def keyword is used to define the normal functions and the lambda keyword is used to create anonymous functions. Please see this for details.
# Python code to illustrate cube of a number # using labmda function cube = lambda x: x * x * x print (cube( 7 )) |
343
Quick Links :
- Quiz on Python Functions
- Difference between Method and Function in Python
- First Class functions in Python
- Recent articles on Python Functions.
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