Hi There, In this post we’ll learn about python functions.

Functions

• Function is a named sequence of statements that performs a computation. When you define a function, you specify the name and the sequence of statements. Later, you can “call” the function by name.

Type conversion functions

• Python provides built-in functions that convert values from one type to another.

int()

• The int() function takes any value and converts it to an integer, if it can, or complains otherwise

    >>> int('32')
    32
    >>> int('hello')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: invalid literal for int() with base 10: 'hello'
    >>>
  

• int() can convert floating-point values to integers, but it doesn’t round off; it chops off the fraction part

    >>> int(13.999)
    13
    >>>
  

float()

• The float() function takes any value and converts it to an integer

    >>> float(32)
    32.0
    >>>
    >>> float("22")
    22.0
    >>>
    >>> float("hii")
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: could not convert string to float: 'hii'
    >>>
  

str()

• The str() function converts its argument to a string

    >>> str(123)
    '123'
    >>>
  

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.

• Example function:

    >>> def print_hi():
    ...     print("Hi")
    ...
    >>> print_hi()
    Hi
    >>>
  

• def is a keyword that indicates that this is a function definition.
• The name of the function is print_hi.
• The rules for function names are the same as for variable names
• The empty parentheses after the name indicate that this function doesn’t take any arguments.
• 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 (four spaces).
• The body can contain any number of statements.

The return key word

• The return statement causes your function to exit and hand back a value to its caller. The point of functions in general is to take in inputs and return something. The return statement is used when a function is ready to return a value to its caller.

• Usage:

    >>> def print_square_of_7():
    ...     print(7**2)
    ...
    >>> print_square_of_7()
    49
    >>>
  
  
    >>> def print_square_of_7():
    ...     7**2
    ...
    >>> res = print_square_of_7()
    >>> print(res)
    None
    >>>
  
    #Using return keyword
    >>> def print_square_of_7():
    ...  return 7**2
    ...
    >>> res = print_square_of_7()
    >>> print(res)
    49
    >>>
  

• Exits the function
• Outputs what ever value is placed after the return keyword
• pops the function off the call stack

Parameters and arguments

• Some of the built-in functions we have seen require arguments. For example, list.append(item) here item is an argument.
• Some functions take more than one arguments example list.insert(index, item)
• Inside the function, the arguments are assigned to variables called parameters

Here is an example of a user-defined function that takes an argument:

• Example:

     >>> def add(num1, num2):
    ...     return num1 + num2 #returningsum of num1 and num2
    ...
    >>> add(2, 3) #num1 and num2 are parameters for add() function
    5
    >>>
  

Parameter:

• A variable in method defination.
• A variable in the decleration of function

Ex:

• In the above add() function num1 and num2 in function defination are parameters

Argument:

• When a method is called, the aurguments are the data you pass into the method’s parameters
• Argument is the avtual value of the variable that gets passed to function.

Ex:

• When we call the add(2, 3) function in the above example 2, 3 are arguments.

Default Parameters

• Usage:

    >>> def exponent(num, power=2):
    ...     return num ** power
    ...
    >>> exponent(3, 3)
    27
    >>> exponent(5)
    25
  

• In the above example function defination we have two parameters

  • num : parameter without default value
  • powrer : parameter with default value

Why to have default parameters

• Allows you to be more defencive
• Avoids errors with incorrect parameters
• Makes the function more reliable

What can be default parameters

• Default parameters can be of any datatype i.e lists, dictonaries, string, bool, int, float

• Default parameters can also be a function

• Example:

    >>>
    >>> def add(a, b):
    ...     return a + b
    ...
    >>> def subtract(a, b):
    ...     return a - b
    ...
    >>> def math(a, b, fn=add): #making add() function as a default parameter
    ...     return fn(a, b)
    ...
    >>> math(2, 3) 
    5
    >>> math(2, 2, subtract) #passing function as a argument
    0
    >>>
  

Keyword arguments

• We can change the order of the arguments while calling a function with the help of keyword arguments

    >>> def full_name(first="Gopikrishna", last="A"):
    ...     return f"{first} {last}"
    ...
    >>> full_name(first="Tony", last="Stark")
    'Tony Stark'
    >>> full_name(last="Stark", first="Tony")
    'Tony Stark'
    >>>
  

• In the above example we can observe that even we change the order of the arguments the result will be same this is because of Keyword arguments

Variable scope

• Variables created in the function are scoped in that function

• Example:

    >>> def say_hello():
    ...     name = "Tony Stark"
    ...     return f"Hello {name}"
    ...
    >>> say_hello()
    'Hello Tony Stark'
    >>>
    >>> print(name)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    NameError: name 'name' is not defined
    >>>
  

• In the above example we got NameError when we tried to print name variable which is defined inside the say_hello() function this is because varables defined inside a function are only aviliable inside the function.

• This can be handled by making the name variable as a global variable as follows

    >>> def say_hello():
    ...     global name
    ...     name = "Stark"
    ...     return f"Hello {name}"
    ...
    >>> say_hello()
    'Hello Stark'
    >>> name
    'Stark'
    >>>