Chapter 3 reserved words, identifiers and built-in functions of the foundation of Python

Web front end practice log 2021-01-19 06:24:04
chapter reserved words identifiers built-in

One 、 Reserved words ( keyword )

Reserved word is python Some words in a language that have been given a specific meaning , This requires developers to develop programs , You can't use these reserved words as identifiers for variables 、 function 、 class 、 Templates and other object naming .

Python List of reserved words

and as assert break class continue
def del elif else except finally
for from False global if import
in is lambda nonlocal not None
or pass raise return try True
while with yield

It should be noted that , because Python It's strictly case sensitive , Reserved words are no exception . therefore , We can say if Is a reserved word , but IF It's not reserved words .

Two 、 identifier

Simply understand , An identifier is a name , It's like each of us has his own name , Its main function is as a variable 、 function 、 class 、 Names of modules and other objects .

python The identifier is not named arbitrarily , It's about following certain rules of command , for instance :

(1) An identifier is made up of characters (A~Z and a~z)、 Underline and numbers make up , But the first character cannot be a number .

(2) Identifiers cannot be with Python The reserved words in are the same . About reserved words , The following chapters will describe in detail .

(3) Python In the identifier in , Cannot contain spaces 、@、% as well as $ Equal special character

(4) stay Python in , The letters in the identifier are Case sensitive Of , in other words , Two identical words , If the size format is different , The meaning of multi representation is also completely different . for instance , The following 3 Between two variables , It's completely independent 、 It doesn't matter , They are independent of each other .

number = 0
Number = 0

(5) Python In language , Identifiers that begin with underscores have a special meaning , for example :

  • · An identifier that starts with a single underline ( Such as _width), Represents a class property that cannot be accessed directly , It cannot pass from...import* How to import ;
  • · Identifiers starting with double underscores ( Such as __add) Represents a private member of a class ;
  • · Identifiers that start and end with double underscores ( Such as __init__), Is a private identifier .

therefore , Unless a particular scenario requires , You should avoid using identifiers that start with underscores .

Let's get familiar with it again Python Some common naming conventions :

(1) Module name : Try to be short , And use all lowercase letters , have access to “_” Split multiple letters , for example :game_main、game_regsiter;

(2) Package name : Also try to be short , And use all lowercase letters , Underline is not recommended . for example :com.mingrisoft、;

(3) Class name : Capitalize a word ( namely Pascal style ), for example : Define a book borrowing class :BorrowBook.

(4) Classes inside modules : Underline “_”+Pascal The class name of the style , for example : stay BorrowBook The inner class of a class :_BorrowBook

(5) function 、 Class properties and method naming rules : Similar to module name , It's also all lowercase letters , Multiple letters can be used “_” Separate

(6) Constant : All in capital letters , You can use underscores “_”

(7) Use single underline “_” The starting module variable or function is protected , In the use of from XXX import * When a statement is imported from a module, these variables or functions cannot be imported

(8) Double underline “__” The first instance variable or method is private to the class .

3、 ... and 、 Built in functions

ptthon The functions that come with the interpreter are called built-in functions , These functions can be used directly , There is no need to import a module

surface by Python 3.x Built in functions

abs() delattr() hash() memoryview() set()
all() dict() help() min() setattr()
any() dir() hex() next() slicea()
ascii() divmod() id() object() sorted()
bin() enumerate() input() oct() staticmethod()
bool() eval() int() open() str()
breakpoint() exec() isinstance() ord() sum()
bytearray() filter() issubclass() pow() super()
bytes() float() iter() print() tuple()
callable() format() len() property() type()
chr() frozenset() list() range() vars()
classmethod() getattr() locals() repr() zip()
compile() globals() map() reversed() __import__()
complex() hasattr() max() round()
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