Day 4 :Everything You Need to Know About Functions in Python

Definition and Defining Functions

A function represents some part of the code which can be executed only when required .In python, user defines the function by using def.

def sum(a,b):
  print(a+b)
def sum(a,b):
  print(a+b)
def sum(a,b):
  print(a+b)

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in this example we have performed a sum of two integers a,b. so.. whenever we require to sum two numbers, we can directly use the function sum(a,b).

Calling a Function

In Python, calling a function means executing the code defined inside a function block by using the function’s name followed by parentheses. Here is an example for how calling is done in python:

def sum(a,b):
  print(a+b)
sum(1,3)
def sum(a,b):
  print(a+b)

sum(1,3)
def sum(a,b):
  print(a+b)

sum(1,3)

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here,

• a and b are the parameters in the function definition.
• 1, 3 are the arguments passed to the function.
• sum is the name of the function

Generally, there are 4 types of Arguments:

1.Required Arguments

Required arguments are the parameters that a function must receive when it is called. If you do not provide the required arguments in a function call, Python will raise a TypeError because the function will not have the necessary information to execute.

sum(a,b):
  print(a+b)
sum(1,3)
sum()
sum(a,b):
  print(a+b)
sum(1,3)

sum()
sum(a,b):
  print(a+b)
sum(1,3)

sum()

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Output: 4
TypeError

Here:

• a and b are required arguments because they do not have a default value.
• So, when you call sum without an argument, Python raises an error.

2. Keyword Arguments

Keyword arguments allow you to pass arguments to a function by explicitly specifying the parameter names.

new_print(a,b):
   print("{a} is a friend of {b}")
new_print(b="Alice" ,a="Bob")
new_print(a,b):
   print("{a} is a friend of {b}")
new_print(b="Alice" ,a="Bob")
new_print(a,b):
   print("{a} is a friend of {b}")
new_print(b="Alice" ,a="Bob")

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Output: Bob is a friend of Alice
Here:

• Since the Arguments are mentioned beforehand, in spite of wrong order, this code will produce this kind of result.

3. Default Arguments

Default arguments in Python allow you to define a function with default values for certain parameters. If a value for a parameter with a default is not provided during the function call, Python automatically assigns the default value. This makes functions more flexible and reduces the need to specify every parameter explicitly.

sum(a=0, b=0):
   print(a+b)
sum()
sum(1,3)
sum(a=0, b=0):
   print(a+b)
sum()
sum(1,3)
sum(a=0, b=0):
   print(a+b)
sum()
sum(1,3)

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Output: 0\n 4
In this example, even though, we have not assigned any variable to a, b since the a and b are assigned to a default value, it will give an output 0

4. Variable Length Arguments

Python provides a way to define functions that can accept a variable number of arguments. Variable-length arguments are handled using:

1. *args (for non-keyword arguments)
2. **kwargs (for keyword arguments)

1. *args:

*args allows a function to accept any number of positional arguments. Inside the function, these arguments are accessible as a tuple.

sum (*numbers):
   sum=0
   for i in numbers:
     sum+=i
   print(sum)
sum(1,2,3,4)
sum (*numbers):
   sum=0
   for i in numbers:
     sum+=i
   print(sum)
sum(1,2,3,4)
sum (*numbers):
   sum=0
   for i in numbers:
     sum+=i
   print(sum)
sum(1,2,3,4)

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Output: 10

2. **Kwargs:

**kwargs allows a function to accept any number of keyword arguments (arguments passed as key=value pairs). These are stored in a dictionary.

sum(**numbers):
  sum=0
  for keys,values in numbers:
     print("{keys}={numbers}")
     sum+= values
sum(**numbers):
  sum=0
  for keys,values in numbers:
     print("{keys}={numbers}")
     sum+= values
sum(**numbers):
  sum=0
  for keys,values in numbers:
     print("{keys}={numbers}")
     sum+= values

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Trick of the Day: 4 ways to swap the numbers

way 1:

P=5
Q=4
temp = P  
P = Q  
Q = temp 
P=5
Q=4
temp = P  
P = Q  
Q = temp 
P=5
Q=4
temp = P  
P = Q  
Q = temp 

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way 2:

P=5
Q=4
P,Q=Q,P
P=5
Q=4
P,Q=Q,P
P=5
Q=4
P,Q=Q,P

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way 3:

P=5
Q=4
P = P ^ Q  
Q = P ^ Q  
P = P ^ Q
P=5
Q=4
P = P ^ Q  
Q = P ^ Q  
P = P ^ Q
P=5
Q=4
P = P ^ Q  
Q = P ^ Q  
P = P ^ Q

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way 4:

P=5
Q=4
P = P + Q    
Q = P - Q   
P = P - Q 
P=5
Q=4
P = P + Q    
Q = P - Q   
P = P - Q 
P=5
Q=4
P = P + Q    
Q = P - Q   
P = P - Q 

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原文链接：Day 4 :Everything You Need to Know About Functions in Python