Learning & 1-- transfer function defined function argument - the Python programming from entry into practice

Defined Functions

DEF greet_user ():
     Print ( " the Hello " ) 


greet_user ()     # after the definition of the functions and classes PEP8 two blank spaces

1. passing arguments to functions

def greet_user(username):
    print("Hello, " + username.title() + "!")


greet_user('ges')

2. arguments and parameters

When the function definition parentheses called variable parameter, eg: username; function call or a variable value becomes the argument in parentheses, EG: ' GES '.

The argument values ​​passed to the function call parameter, run the function thereof.

Pass arguments

1. Location argument

Function call, each argument in the function call is associated to the function definition in a parameter, based on the associated argument sequential manner - Location argument.

def describe_pet(animal_type, pet_name):
    print("\nI have a " + animal_type + '.')
    print("My " + animal_type + "'s name is " + pet_name.title() + ".")


describe_pet('dog', 'pipi')

operation result:

I have a dog.
My dog's name is Pipi.

Argument position: automatically from left to right the first real function call parameters passed to the first parameter, the second argument to the second parameter, sequentially. . .

• Function can be called multiple times: In order to improve efficiency, then define a function that can be called multiple times, just using different arguments can be.
• Note that the order of the arguments: the order of the arguments should be consistent with the order of the parameter, or will farce.

2. Keyword argument

describe_pet(animal_type='dog', pet_name='pipi')
describe_pet(pet_name='pipi', animal_type='dog')

 Run a result of the two function call code is exactly the same.

Passed to the parameter name - value pairs, when the function call without regard to the order of arguments.

3. Default value

def describe_pet(pet_name, animal_type='dog'):
    print("\nI have a " + animal_type + '.')
    print("My " + animal_type + "'s name is " + pet_name.title() + ".")


describe_pet(pet_name='wangwang')    # 使用默认值
describe_pet('wangwang')    # 使用默认值 &Argument position
describe_pet (pet_name = ' Mimi ' , animal_type = ' CAT ' )     # override the default value of the parameter, the new argument value transfer

operation result:

I have a dog.
My dog's name is Wangwang.

I have a dog.
My dog's name is Wangwang.

I have a cat.
My cat's name is Mimi.

4. Equivalent function calls

Position can be mixed arguments, argument a keyword and default values, forming a plurality of operation results consistent function call - referred to as the equivalent function call.

5. Avoid argument error

def describe_pet(pet_name, animal_type):
    print("\nI have a " + animal_type + '.')
    print("My " + animal_type + "'s name is " + pet_name.title() + ".")


describe_pet()

 operation result:

Traceback (most recent call last):
  File "C:\Users\yxf\Desktop\python_pycharm\test_def.py", line 6, in <module>
    describe_pet()
TypeError: describe_pet() missing 2 required positional arguments: 'pet_name' and 'animal_type'

When the arguments and parameters do not match, an error message will be operating details, according to the code modification message.