Python assert 的帮助函数

Question

help 功能不适用于 assert？为什么？

>>> help(assert)
  File "<stdin>", line 1
    help(assert)
         ^
SyntaxError: invalid syntax

Answer 1

因为 assert 是语句而不是 function/object design of python: why is assert a statement and not a function?

也是如此

help(if)

Answer 2

要获取关键字的帮助，您需要传递关键字的字符串名称

>>> help('assert')
The "assert" statement
**********************

Assert statements are a convenient way to insert debugging assertions
into a program:

   assert_stmt ::= "assert" expression ["," expression]

The simple form, "assert expression", is equivalent to

   if __debug__:
       if not expression: raise AssertionError

The extended form, "assert expression1, expression2", is equivalent to

   if __debug__:
       if not expression1: raise AssertionError(expression2)

These equivalences assume that "__debug__" and "AssertionError" refer
to the built-in variables with those names.  In the current
implementation, the built-in variable "__debug__" is "True" under
normal circumstances, "False" when optimization is requested (command
line option "-O").  The current code generator emits no code for an
assert statement when optimization is requested at compile time.  Note
that it is unnecessary to include the source code for the expression
that failed in the error message; it will be displayed as part of the
stack trace.

Assignments to "__debug__" are illegal.  The value for the built-in
variable is determined when the interpreter starts.

您只能在作为函数、类、模块或方法的对象上使用help。

>>> help(min)
Help on built-in function min in module builtins:

min(...)
    min(iterable, *[, default=obj, key=func]) -> value
    min(arg1, arg2, *args, *[, key=func]) -> value

    With a single iterable argument, return its smallest item. The
    default keyword-only argument specifies an object to return if
    the provided iterable is empty.
    With two or more arguments, return the smallest argument.

如果您尝试对 关键字 使用帮助，您会收到语法错误，因为它们既不是对象也不是字符串

>>> help(assert)
SyntaxError: invalid syntax
>>> help(while)
SyntaxError: invalid syntax
>>> help(if)
SyntaxError: invalid syntax

More details

Invoke the built-in help system. (This function is intended for interactive use.) If no argument is given, the interactive help system starts on the interpreter console. If the argument is a string, then the string is looked up as the name of a module, function, class, method, keyword, or documentation topic, and a help page is printed on the console. If the argument is any other kind of object, a help page on the object is generated.

Answer 3

因为assert是一个语句。你可以做 help('assert')

输出：

>>> help('assert')
The "assert" statement
**********************

Assert statements are a convenient way to insert debugging assertions
into a program:

   assert_stmt ::= "assert" expression ["," expression]

The simple form, "assert expression", is equivalent to

   if __debug__:
       if not expression: raise AssertionError

The extended form, "assert expression1, expression2", is equivalent to

   if __debug__:
       if not expression1: raise AssertionError(expression2)

These equivalences assume that "__debug__" and "AssertionError" refer
to the built-in variables with those names.  In the current
implementation, the built-in variable "__debug__" is "True" under
normal circumstances, "False" when optimization is requested (command
line option "-O").  The current code generator emits no code for an
assert statement when optimization is requested at compile time.  Note
that it is unnecessary to include the source code for the expression
that failed in the error message; it will be displayed as part of the
stack trace.

Assignments to "__debug__" are illegal.  The value for the built-in
-- More  --

Python assert 的帮助函数

Python help function for assert

python

assert

helper