Python Basics: Python functions

The function is the most used object in Python.

Simple Rules for function definitions:

1, defined with Def, followed by the function name and parameters and colon, format:

2, the function internal code block needs to indent

3, return the function value with return, the default return value is None

Format:

def function name (parameter):

code block

Return #可有可无 can also be used anywhere in the code block

Second, the use of return in the function:

Return can be used anywhere in the function, jumping directly out of the current function, ignoring other blocks of code.

# return can also be returned without parameters, returning the None

# you can have no return, and none of them return.

# return can also return a dictionary, list, function (the adorner is the function code block returned).

1, can jump out of if,while,for and other statements

Def use_return (): i = 0 while true:i + = 1 for j in Range (i): Print (J, end= ") If j = = 5:return J print () Use_return () # Run Result: I equals 5 will end Function "" "001012012301234 012345 "" "

The above function changes the calling method:

Print (Use_return ()) # The last line 0123455, and the last 5 is the value of the return function, which is the value of J. Try to break the last 5 line.

2. Call Function:

Functions are called using function names and parentheses. The function body is called without parentheses, which is equivalent to an individual name.

#  uses the above example #  call 1if use_return ()  == 5:    print (5) #  call 2for  i in range (0,use_return ()):                     print (i) #不能使用, because Use_return () returns a number, but not an int, it must first be assigned to a variable. Then call the variable V = use_return () for i in range (0,v):                     print (i)      #  call 3s = use_return () print (s) #  call function Body Func = use_returnprint (func)                           #  printed is the memory address of the Use_return function func ()                                #  Running Use_return function 

Third, the relationship between the function variables and the external variables:

1. Can change (mutable) and non-change (immutable) objects

strings, tuples, and numbers are immutable objects, while list,dict and so on are objects that can be modified.

2. Immutable Type:

# variable Assignment a=5 after the assignment of a=10, not the value of a changed, the variable is equivalent to a pointer, but the pointer is changed, 5 itself does not change, the point of 10 is a new address, instead of 5 into 10.

# Immutable types are passed into the function, and after the function is modified, the external variable values are not affected.

3. Variable type:

# variable Assignment la=[1,2,3,4] and then assign value la[2]=5, although the memory address that La points to does not change, but the internal value has changed, so it is mutable.

# a mutable type is inside the function of La itself, so modify la[2 within the function], and also change the la[2 outside the function]

def MODIFY_LA2 (La_value): la_value[2] = 99999la = [0, 1, 2, 3, 4, 5]MODIFY_LA2 (LA) print (' La =%s '% LA) # run result la = [0, 1 , 99999, 3, 4, 5]

4. Function variables look for the outermost layer

Def MODIFY_LA2 (): la[2] = 99999la = [0, 1, 2, 3, 4, 5]MODIFY_LA2 () print (' La =%s '% la) #modify_la2找不到la, the La,la outside the function must be written In front of the MODIFY_LA2 () call

Five, the function of the parameter transfer form:

1. Required parameters: When calling a function, write the corresponding value in the order of the variables

2. Keyword parameter: When calling a function, use variable name to assign value, variable = value

3. Default parameters: Parameter with value when defining function, Def user (name, age=20):, age=20 is the default parameter

4, indefinite length parameter:

# (*ARGS) variable length parameter, can only receive the necessary parameters, convert the parameters to list storage

# (**KWARGS) variable length parameter, can only receive the keyword parameters, and convert the parameters to dictionary storage

5. The order in which the parameters exist:

Required parameters, default parameters, *args, **kwargs

def MODIFY_LA2 (name, age=20, *args, **kwargs):

#age默认参数不起作用, the value must be assigned.

def MODIFY_LA2 (name, age=20, *args, **kwargs): Print (' name= ', name) print (' age= ', ' Age ') (' args= ', args) pr Int (' kwargs= ', Kwargs) modify_la2 (' dage ', ' Men ', 175, skill= ' pain ', father= ' ADW ') # Run results name= dageage= menargs= (175,) kwargs= {' father ': ' Adw ', ' skill ': ' Pain '}

Vi. anonymous function lambda

The body of a lambda is an expression, not a block of code. Only a finite amount of logic can be encapsulated in a lambda expression.

The lambda function has its own namespace and cannot access parameters outside its own argument list or in the global namespace.

Format:

Lambda [arg1 [, Arg2,..... argn]]:expression

#梯形面积公式: Resault = lambda x1, x2, H: (x1 + x2) *h/2print (Resault (1, 2, 4))

Python Basics: Python functions