有少量常量存活在内置命名空间中。它们是：
False
¶
False 值的
bool
类型。赋值
False
是非法的和引发
SyntaxError
.
True
¶
True 值的
bool
类型。赋值
True
是非法的和引发
SyntaxError
.
None
¶
The sole value of the type
NoneType
.
None
is frequently used to represent the absence of a value, as when default arguments are not passed to a function. Assignments to
None
是非法的和引发
SyntaxError
.
NotImplemented
¶
Special value which should be returned by the binary special methods (e.g.
__eq__()
,
__lt__()
,
__add__()
,
__rsub__()
, etc.) to indicate that the operation is not implemented with respect to the other type; may be returned by the in-place binary special methods (e.g.
__imul__()
,
__iand__()
, etc.) for the same purpose. Its truth value is true.
注意
When a binary (or in-place) method returns
NotImplemented
the interpreter will try the reflected operation on the other type (or some other fallback, depending on the operator). If all attempts return
NotImplemented
, the interpreter will raise an appropriate exception. Incorrectly returning
NotImplemented
will result in a misleading error message or the
NotImplemented
value being returned to Python code.
见 实现算术运算 范例。
注意
NotImplementedError
and
NotImplemented
are not interchangeable, even though they have similar names and purposes. See
NotImplementedError
for details on when to use it.
Ellipsis
¶
The same as the ellipsis literal “
...
”. Special value used mostly in conjunction with extended slicing syntax for user-defined container data types.
注意
名称
None
,
False
,
True
and
__debug__
无法重新赋值 (赋值它们，即使作为属性名称，引发
SyntaxError
)，所以它们可以被认为是真常量。
site
模块
¶
site
module (which is imported automatically during startup, except if the
-S
command-line option is given) adds several constants to the built-in namespace. They are useful for the interactive interpreter shell and should not be used in programs.
quit
(
code=None
)
¶
exit
(
code=None
)
¶
Objects that when printed, print a message like “Use quit() or Ctrl-D (i.e. EOF) to exit”, and when called, raise
SystemExit
with the specified exit code.
copyright
¶
credits
¶
Objects that when printed or called, print the text of copyright or credits, respectively.
license
¶
Object that when printed, prints the message “Type license() to see the full license text”, and when called, displays the full license text in a pager-like fashion (one screen at a time).