27.2. "pydoc" — Documentation generator and online help system
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**Source code:** Lib/pydoc.py

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The "pydoc" module automatically generates documentation from Python
modules.  The documentation can be presented as pages of text on the
console, served to a Web browser, or saved to HTML files.

For modules, classes, functions and methods, the displayed
documentation is derived from the docstring (i.e. the "__doc__"
attribute) of the object, and recursively of its documentable members.
If there is no docstring, "pydoc" tries to obtain a description from
the block of comment lines just above the definition of the class,
function or method in the source file, or at the top of the module
(see "inspect.getcomments()").

The built-in function "help()" invokes the online help system in the
interactive interpreter, which uses "pydoc" to generate its
documentation as text on the console.  The same text documentation can
also be viewed from outside the Python interpreter by running
**pydoc** as a script at the operating system’s command prompt. For
example, running

   pydoc sys

at a shell prompt will display documentation on the "sys" module, in a
style similar to the manual pages shown by the Unix **man** command.
The argument to **pydoc** can be the name of a function, module, or
package, or a dotted reference to a class, method, or function within
a module or module in a package.  If the argument to **pydoc** looks
like a path (that is, it contains the path separator for your
operating system, such as a slash in Unix), and refers to an existing
Python source file, then documentation is produced for that file.

Note: In order to find objects and their documentation, "pydoc"
  imports the module(s) to be documented.  Therefore, any code on
  module level will be executed on that occasion.  Use an "if __name__
  == '__main__':" guard to only execute code when a file is invoked as
  a script and not just imported.

When printing output to the console, **pydoc** attempts to paginate
the output for easier reading.  If the "PAGER" environment variable is
set, **pydoc** will use its value as a pagination program.

Specifying a "-w" flag before the argument will cause HTML
documentation to be written out to a file in the current directory,
instead of displaying text on the console.

Specifying a "-k" flag before the argument will search the synopsis
lines of all available modules for the keyword given as the argument,
again in a manner similar to the Unix **man** command.  The synopsis
line of a module is the first line of its documentation string.

You can also use **pydoc** to start an HTTP server on the local
machine that will serve documentation to visiting Web browsers.
**pydoc -p 1234** will start a HTTP server on port 1234, allowing you
to browse the documentation at "http://localhost:1234/" in your
preferred Web browser. Specifying "0" as the port number will select
an arbitrary unused port.

**pydoc -n <hostname>** will start the server listening at the given
hostname.  By default the hostname is ‘localhost’ but if you want the
server to be reached from other machines, you may want to change the
host name that the server responds to.  During development this is
especially useful if you want to run pydoc from within a container.

**pydoc -b** will start the server and additionally open a web browser
to a module index page.  Each served page has a navigation bar at the
top where you can *Get* help on an individual item, *Search* all
modules with a keyword in their synopsis line, and go to the *Module
index*, *Topics* and *Keywords* pages.

When **pydoc** generates documentation, it uses the current
environment and path to locate modules.  Thus, invoking **pydoc spam**
documents precisely the version of the module you would get if you
started the Python interpreter and typed "import spam".

Module docs for core modules are assumed to reside in
"https://docs.python.org/X.Y/library/" where "X" and "Y" are the major
and minor version numbers of the Python interpreter.  This can be
overridden by setting the "PYTHONDOCS" environment variable to a
different URL or to a local directory containing the Library Reference
Manual pages.

Changed in version 3.2: Added the "-b" option.

Changed in version 3.3: The "-g" command line option was removed.

Changed in version 3.4: "pydoc" now uses "inspect.signature()" rather
than "inspect.getfullargspec()" to extract signature information from
callables.

Changed in version 3.7: Added the "-n" option.
