Day Everything You Need to Know About Functions in Python

Detailed explanation of Python functions: definition, call and parameter types

Function definition and function

A function is a reusable block of code that is executed only when needed. In Python, functions are defined using the def keyword.

For example, the following code defines a sum function:

<code class="language-python">def sum(a, b):
  print(a + b)</code>

This function calculates the sum of two integers a and b. When you need to find the sum of two numbers, you can directly call the sum(a, b) function.

Function call

Calling a function means executing the code inside the function through the function name followed by parentheses. For example:

<code class="language-python">def sum(a, b):
  print(a + b)

sum(1, 3)</code>

Here:

• a and b are parameters in the function definition.
• 1 and 3 are the parameter values ​​(actual parameters) passed to the function.
• sum is the function name.

Parameter type

Python functions support four parameter types:

1. Required parameters: Parameters that must be provided when the function is called. If not provided, Python will throw a TypeError exception.

<code class="language-python">def sum(a, b):
  print(a + b)

sum(1, 3)  # 正确
sum()      # TypeError</code>

a and b are required parameters as they have no default value.

2. Keyword arguments: Pass parameters by explicitly specifying the parameter name.

<code class="language-python">def new_print(a, b):
   print(f"{a} is a friend of {b}")

new_print(b="Alice", a="Bob")</code>

Output: Bob is a friend of Alice

Keyword parameters correctly assign values ​​to the corresponding parameters even if the parameters are in the wrong order.

3. Default parameter: Set the default value for the parameter, which can be omitted when calling the function.

<code class="language-python">def sum(a=0, b=0):
   print(a + b)

sum()      # 输出：0
sum(1, 3)  # 输出：4</code>

Even if no values ​​for a and b are provided, the function will execute normally because they have a default value of 0.

4. Variable parameters: The function can accept any number of parameters.

   a. *args: used to receive any number of non-keyword parameters, accessed in the form of tuples inside the function.

<code class="language-python">def sum(*numbers):
   total = 0
   for i in numbers:
     total += i
   print(total)

sum(1, 2, 3, 4)  # 输出：10</code>

b. **kwargs: used to receive any number of keyword parameters, accessed in the form of a dictionary inside the function.

<code class="language-python">def print_kwargs(**kwargs):
  for key, value in kwargs.items():
     print(f"{key}={value}")

print_kwargs(name="Alice", age=30, city="New York")</code>

Four methods of digital exchange

The following four methods can exchange the values ​​​​of two numbers:

Method 1: Use temporary variables

<code class="language-python">P = 5
Q = 4
temp = P
P = Q
Q = temp</code>

Method 2: Tuple unpacking

<code class="language-python">P = 5
Q = 4
P, Q = Q, P</code>

Method 3: Use bitwise operators

<code class="language-python">P = 5
Q = 4
P = P ^ Q
Q = P ^ Q
P = P ^ Q</code>

Method 4: Use addition and subtraction

<code class="language-python">P = 5
Q = 4
P = P + Q
Q = P - Q
P = P - Q</code>

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