python And c++ Different , No pointer

1. Is a multiplication symbol

a=1
b=2
c=a*b
Output c Certainly 1×2=2. I believe this is not the focus of our concern .

2. Collect extra values in the list

In this way, it is not necessary to ensure that the number of hedges is the same as the number of variables . for instance ：

a,b,c=[1,2,3,4]
c Ahead No. is mainly used to collect parameters . So output a, yes 1; Output b, yes 2, Output c, yes [3,4]. Notice that the list is collected here .

3. Functions are involved ,* No. is used to collect parameters or allocate parameters .

Specific use , It's for reading * No. is used when a function is defined or called .（ This sentence is very important ！）

3.1 If you define a function ,* Represents collection parameters ,** Represents the collection of keyword parameters .

3.1.1 When defining a function , One * The situation of ：

At this time, if the following method is used to call myprint

So the function is to call all the values provided , Put it in a tuple .

Follow up 2 There is a difference between the two ,2 Here are the extra parameters in the collection list , Here is the collection of good parameters , Put them into tuples .

In this case , In the parameter of function definition *params Back , You'd better not add any other formal parameters , For example, you define it as def myprint(*params,x) , When called myprint（1,2,3）, You're going to report a mistake . Because of this python I can't tell which data is for params Of . If you have to define it that way , But when it is called , What must be displayed indicates which value is given to x Of . such as myprint（1,2,x=3）, Call in this way so that there is no error .

3.1.2 When defining a function , Two ** The situation of ：

For the previous parameter is *params The situation of ,myprint Keyword parameters cannot be passed in . What do you mean , Is still defined in this way ：

This is wrong ：

because * No. does not collect keyword parameters . Therefore, it needs to be modified in the following ways , Use two asterisks ：

This call myprint2 There will be no problem ：

Get a dictionary . The order of the elements in the dictionary depends on your environment .

3.2 If you call a function ,* and ** Are used to allocate parameters

3.2.1 When you call a function , One * The situation of ：

for example , It's just that print function

Now there are two formal parameters , But can I just pass in one parameter ？

Yes ,“ Assign parameters when calling a function ” Follow “ Collect parameters when defining a function ”, In turn ！

Suppose you have a tuple ：

params=(1,2)
You can call myprint function ：

myprint(*params)
You can output ：

3.2.2 When you call a function , Two ** The situation of ：

And above 3.1.2 It's like , Is the assignment dictionary Of .

This time params It's a dictionary ：

params={‘x’:1,‘y’:2}
You can call myprint function ：

myprint(**params)
You can output ：