What are the naming rules for python identifiers

In Python, everything is an object, including constant data types, such as integer data types (1,2,3...), string data types ("ABC") . To use these objects, use their object references. The assignment operator actually makes the object reference refer to the object storing data in memory.

So what is an identifier?

Identifier is a name given to an object reference.

Valid Python identifier rules:

1. The length is arbitrary;

2. The identifier cannot have the same name as the keyword;

3. In the 2.x version of Python, identifiers start with ASCII letters or underscores, and can be followed by letters, numbers, and underscores; in Python 3.x, identifiers start with ASCII letters, underscores, and most Letters in non-English languages, as long as they are Unicode-encoded letters, can serve as guide characters, and subsequent characters can be any guide characters, or any non-space characters, including any characters considered to be numbers in Unicode encoding. (So ​​naming can be done using Arabic, Chinese, Japanese or Russian characters, or characters from any other language supported by the Unicode character set)

Convention:

1. Do not use Python’s predefined identifier names, so avoid using names such as NotImplemented and Eliipsis, which may be used by new versions of Python in the future;

2. Do not use Python built-in function names or built-in data The type or exception name is used as the identifier name;

3. Regarding the convention of underscores, the use of underscores at the beginning and end of the name should be avoided, because Python uses a large number of such names to define various special methods and Variables; in some cases, names that begin with one or two underscores but do not end with two underscores should be treated specially.

Example

>>> math=2
>>> math2

The above statement is legal, but it will re-bind the object reference bound to the math data type to the int data type object , then the attributes of the math data type will not be used normally.

>>> int=2
>>> int2

Same as above, legal but not recommended.

#合法
a123_=2   
_a123=2
我=2        #中文
α=2         #希腊字母

#不合法的标识符名
a-b=2        #因为包含了减法操作符，'-'不是一个Unicode字母、数字、下划线，不能将2赋值给操作符
2miles=2     #不能数字开头
I'm=2        #单引号不是一个Unicode字母、数字或下划线

There is one more thing to say about underscores:

A single underscore can be used as an identifier. Within the interactive interpreter or Python shell, the underscore actually stores the last evaluated character. The result of the expression. In a normally running program, the use of underscores, like other ordinary identifiers, needs to be predefined by yourself and is not owned by the system.

If you don’t care about the data items for iteration, some programmers like to use _ in for...in.., such as:

#没有使用到迭代的数据项
for _ in (0,1,2,3,4,5):
    print("Hello")

Also note that some programming is internationalized Programmers of programs generally use _ as the name of their translation functions. These programmers generally do not use gettext("translate me"), but _("translate me").

When the variable is private, it is a good habit to use _xxx to represent the variable.

In a class, the member variables starting with "single underscore" are called protected variables, which means that only class objects and subclass objects themselves can access these variables. They need to be accessed through the interface provided by the class, and cannot be accessed with " "from xxx import *" to import; "double underscore" starts with the private members of the class, which means that only the class object itself can access this data, and even subclass objects cannot access this data. (__foo__) starting and ending with a double underscore represents a special method-specific identifier in Python, such as __init__() representing the constructor of a class.

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