How do I see the Python doc on Linux?

Online documentation

The simplest way is to use Google to get to online documentation. There is no single point where you find all documentations of all modules. However, a few common ones are:

• Python 3
• NumPy and SciPy
• Theano

If you need offline documentation there are a few other possibilities:

Download it

You can download the documentation as HTML or a PDF: https://docs.python.org/3/download.html

When you have a web server running, you can use the HTML version and access it as you are used to via a browser. The HTML site looks just like you are used to. Even the search works offline, because it is implemented with JavaScript.

PyDoc

Some distributions like Debian offer a python-doc package. You can access it via
pydoc -p [some port number] or via pydoc -g. This will create a local web server. Then you can open your browser and have a look at it:

Console: help(…)

The Python interactive console has a built-in help(...) system. You can either invoke it without an argument:

$ python
Python 2.7.5+ (default, Feb 27 2014, 19:37:08) 
[GCC 4.8.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> help()

Welcome to Python 2.7!  This is the online help utility.

If this is your first time using Python, you should definitely check out
the tutorial on the Internet at http://docs.python.org/2.7/tutorial/.

Enter the name of any module, keyword, or topic to get help on writing
Python programs and using Python modules.  To quit this help utility and
return to the interpreter, just type "quit".

To get a list of available modules, keywords, or topics, type "modules",
"keywords", or "topics".  Each module also comes with a one-line summary
of what it does; to list the modules whose summaries contain a given word
such as "spam", type "modules spam".

help> 

or you can call it with a paramter about which you want to know something. That can be anything (a module, a class, a function, an object, …). It looks like this:

>>> a = {'b':'c'}
>>> help(a)
Help on dict object:

class dict(object)
 |  dict() -> new empty dictionary
 |  dict(mapping) -> new dictionary initialized from a mapping object's
 |      (key, value) pairs
 |  dict(iterable) -> new dictionary initialized as if via:
 |      d = {}
 |      for k, v in iterable:
 |          d[k] = v
 |  dict(**kwargs) -> new dictionary initialized with the name=value pairs
 |      in the keyword argument list.  For example:  dict(one=1, two=2)
 |  
 |  Methods defined here:
 |  
 |  __cmp__(...)
 |      x.__cmp__(y) <==> cmp(x,y)
 |  
 |  __contains__(...)
 |      D.__contains__(k) -> True if D has a key k, else False
 |  
 |  __delitem__(...)
 |      x.__delitem__(y) <==> del x[y]
 |  
 |  __eq__(...)
 |      x.__eq__(y) <==> x==y
 |  
 |  __ge__(...)
 |      x.__ge__(y) <==> x>=y
 |  
 |  __getattribute__(...)
 |      x.__getattribute__('name') <==> x.name
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |  
 |  __gt__(...)
: (scroll)