学习思路：

查看github项目的源码，每个方法都有介绍及使用说明

https://github.com/mherrmann/selenium-python-helium/blob/master/helium/__init__.py

Starting a browser  # 打开浏览器

Helium currently supports Chrome and Firefox. You can start them with the following functions:

Headless browser  

When you type the above commands, you will actually see a browser window open. This is useful for developing your scripts. However, once you run them, you may not want this window to appear. You can achieve this by adding headless=True:

(Similarly for start_firefox(...) of course.)

Interacting with a web site  # 与web交互

The following example shows the most typical statements in a Helium script: 

Most of your own code will (hopefully) be as simple as the above.

Element types  # 元素类型

The above example used pure strings such as Sign in to identify elements on the web page. But Helium also lets you target elements more specifically. For instance:

• Link('Sign in')
• Button('Sign in')
• TextField('First name')
• CheckBox('I accept')
• RadioButton('Windows')
• Image(alt='Helium logo')

You can pass them into other functions such as click(Link('Sign in')). But you can also use them to read data from the web site. For instance:

A common use case is to use .exists() to check for the existence of an element. For example:

I also often find Text(...).valueuseful for reading out data:

For a full list of element types and their properties, please see the source code.

 举例：

click

def click(element):
   """
   :param element: The element or point to click.
   :type element: str, unicode, :py:class:`HTMLElement`, \
:py:class:`selenium.webdriver.remote.webelement.WebElement` or :py:class:`Point`

   Clicks on the given element or point. Common examples are::

      click("Sign in")
      click(Button("OK"))
      click(Point(200, 300))
      click(ComboBox("File type").top_left + (50, 0))
   """

Text

class Text(HTMLElement):
   """
   Lets you identify any text or label on a web page. This is most useful for
   checking whether a particular text exists::

      if Text("Do you want to proceed?").exists():
          click("Yes")

   ``Text`` also makes it possible to read plain text data from a web page. For
   example, suppose you have a table of people's email addresses. Then you
   can read John's email addresses as follows::

      Text(below="Email", to_right_of="John").value

   Similarly to ``below`` and ``to_right_of``, the keyword parameters ``above``
   and ``to_left_of`` can be used to search for texts above and to the left of
   other web elements.
   """