Software Testing/Test Development丨Study Notes Python Functions

python function

What the function does

Functions are organized, reusable code segments used to implement a single or related function
Functions improve application modularity and code reuse
Python built-in functions: docs.python.org/zh-cn/3.8/l…

function definition

def: function definition keyword
function_name: function name
(): The location where the parameter list is placed, which can be empty
parameter_list: optional, specifies the parameters passed to the function
comments: optional, specify comments for the function
function_body: optional, specify the function body

def function_name([parameter_list]):
    [''' comments ''']
    [function_body]

Things to note when defining functions

Indentation: python judges code blocks through strict indentation
- The function body and comments must maintain a certain indentation relative to the def keyword, usually 4 spaces.
- pycharm automatic formatting shortcut keys:ctrl+alt+L
Define empty function
- Use pass statement placeholder
- Write function comments comments

function call

function_name: function name
parameter_value: optional, specify the value of each parameter

function_name([parameter_value])

Parameter passing

Formal parameters: When defining a function, the parameters in parentheses after the function name
Actual parameters: When calling a function, the parameters in parentheses after the function name

# a, b, c 为形式参数
def demo_func(a, b, c):
    print(a, b, c)

# 1, 2, 3 为实际参数
demo_func(1, 2, 3)

Positional parameters

The quantity must be the same as when defined
The location must be the same as when defined

def demo_func(a, b, c):
    print(a, b, c)

# 1 赋值给 a, 2 赋值给 b, 3 赋值给 c
demo_func(1, 2, 3)

keyword arguments

Use formal parameter names to determine input parameter values
Does not need to exactly match the position of the formal parameters

def demo_func(a, b, c):
    print(a, b, c)

demo_func(a=1, b=2, c=3)

Set default values for parameters

You can specify default values for formal parameters when defining a function
Formal parameters that specify default values must be placed at the end of all parameters, otherwise a syntax error will occur.
param=default_value: Optional, specify the parameter and set the default value for the parameter to default_value

def function_name(..., [param=default_value]):
    [function_body]

function return value

value: optional, specifies the value to be returned

def function_name([parameter_list]):
    [''' comments ''']
    [function_body]
    return [value]

Python function advanced and parameter processing

variable parameter

Variable parameters are also called variable length parameters
The actual parameters passed into the function can be any number
common forms
- *args
- **kwargs

*args

Receives any number of actual arguments and puts them into a tuple
To use an existing list or tuple as a variable parameter of a function, you can add*

def print_language(*args):
    print(args)

print_language("python", "java", "php", "go")

params = ["python", "java", "php", "go"]
print_language(*params)

**quargs

Receives any number of actual parameters that are explicitly assigned like keyword parameters and puts them into a dictionary
To use an existing dictionary as a variable parameter of a function, you can add**

def print_info(**kwargs):
    print(kwargs)

print_info(Tom=18, Jim=20, Lily=12)

params = {'Tom':18, 'Jim':20, 'Lily':12}
print_info(**params)

python lambda expression

anonymous function

function without name
Create anonymous functions using lambda expressions

scenes to be used

Need a function, but don’t want to bother naming it?
Usually in scenarios where this function is only used once
Short callback functions can be specified

grammar

result: call lambda expression
[arg1 [, arg2, …. , argn]]: optional, specifies the parameter list to be passed
expression: required, specify an expression to implement a specific function

result = lambda [arg1 [, arg2, .... , argn]]: expression

book_info = [
    ("python", 80),
    ("java", 70),
    ("ruby", 90),
]
book_info_sorted = sorted(book_info, key=lambda x: x[1])
print('sorted(book_info) returns:', book_info_sorted)

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