Follow the turtle up master to learn Python - functions (1)

The main function of the function ： Packaging code . benefits ：1. Maximize code duplication , Reduce redundant code .2. Code with different functions can be encapsulated 、 decompose , So as to reduce the complexity of the structure , Improve the readability of the code .

Create and invoke Code ： use def To define a function , Write the function name directly when calling .

>>> def myfunc():
    for i in range(3):
        print('i love fishc')        
>>> myfunc
<function myfunc at 0x0000016F2DB70A60>  // Error reason not written (), You cannot write only the function name when calling a function
>>> myfunc()
i love fishc
i love fishc
i love fishc

The parameters of the function ： Realize the personalized design of functions through parameters , Parameters can be multiple , There are formal parameters and actual parameters , Formal parameters ： The name of the parameter written when the function is defined , The actual parameter ： Parameters passed in when calling a function .

>>> def myfunc(name):
    for i in range(3):
        print(f'i love {name}')

        
>>> myfunc(python)
Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    myfunc(python)
NameError: name 'python' is not defined        //python No quotes , The expression in quotation marks is a character .

Correct code ：
>>> def myfunc(name):
    for i in range(3):
        print(f"i love {name}.")                      // Use f character string take name Characters of

        
>>> myfunc("python")                 // Be sure to quote
i love python.
i love python.
i love python.

In the case of multiple parameters ：

>>> def myfunc(name, times):
    for i in range(times):
        print(f'i love {name}.')

        
>>> myfunc("python", 5)
i love python.
i love python.
i love python.
i love python.
i love python.

Function return value ： Use return Statement can make the custom function implementation return . Function execution return Statement will immediately return directly to , It doesn't matter if there are other statements .

>>> def div(x, y)
SyntaxError: invalid syntax              // Be sure to use a colon , At the time of definition
>>> def div(x, y):
    z = x / y
    return z

>>> div(2, 1)
2.0
>>> def div(x, y):
    return x / y

>>> div(2, 1)
2.0
>>> def div(x, y):
    if y == 0:
        return " The divisor cannot be zero 0"
    else:
        return x / y

    
>>> div(6, 0)
' The divisor cannot be zero 0'
>>> div(6, 3)
2.0

If we fail a function return Statement to display the returned contents , Then it will execute everything in the function body , Return to one None.

>>> def myfunc():
    pass

>>> print(myfunc())
None