03 关键字？保留字？预留字？

结论

• 在 Python 中，不要多想，keyword 就是“关键字”

• Python3.4 有 33 个关键字

• Python3.7 有 35 个关键字

• 官网中点击 What’s New In Python 3.7，查找 keywords 就能看到增加的两个关键字

  async and await are now reserved keywords

查看

方式一

>>> help("keywords")

Here is a list of the Python keywords.  Enter any keyword to get more help.

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

>>> 
>>> help(None)  # 三个大写开头的直接用 help 即可
Help on NoneType object:

class NoneType(object)
 |  Methods defined here:
 |  
 |  __bool__(self, /)
 |      self != 0
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.

>>> 
>>> help("break")  # 首字母非大写的需要先变成字符串，再 help
The "break" statement
*********************

   break_stmt ::= "break"

"break" may only occur syntactically nested in a "for" or "while"
loop, but not nested in a function or class definition within that
loop.

It terminates the nearest enclosing loop, skipping the optional "else"
clause if the loop has one.

If a "for" loop is terminated by "break", the loop control target
keeps its current value.

When "break" passes control out of a "try" statement with a "finally"
clause, that "finally" clause is executed before really leaving the
loop.

Related help topics: while, for

>>> 

方式二

>>> import keyword
>>> keyword.kwlist
['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
>>> 

补充

• 对 Java 而言，“关键字”与“保留字”有所不同
  • goto, const 等是“保留字”但不是“关键字”
  • 简单地说，它们不能作为标识符，但也不是关键字
• 这些“保留字”，就像有些电影公司买下 IP，自己不拍，别人也不能拍
• 翻译关系，也有“预留字”的说法，有时候指关键字，有时候指保留字，视具体情况而定了