先列出selenium所有方法，然后挨个使用！说明
add_cookie
application_cache
back
capabilities
close
command_executor
create_web_element
current_url
current_window_handle
delete_all_cookies
delete_cookie
desired_capabilities
error_handler
execute
execute_async_script
execute_script
find_element
find_element_by_class_name
find_element_by_css_selector
find_element_by_id
find_element_by_link_text
find_element_by_name
find_element_by_partial_link_text
find_element_by_tag_name
find_element_by_xpath
find_elements
find_elements_by_class_name
find_elements_by_css_selector
find_elements_by_id
find_elements_by_link_text
find_elements_by_name
find_elements_by_partial_link_text
find_elements_by_tag_name
find_elements_by_xpath
forward
get
get_cookie
get_cookies
get_screenshot_as_base64
get_screenshot_as_file
get_window_position
get_window_size
implicitly_wait
is_online
maximize_window
name
orientation
page_source
quit
refresh
save_screenshot
service
session_id
set_page_load_timeout
set_script_timeout
set_window_position
set_window_size
start_client
start_session
stop_client
switch_to_active_element
switch_to_alert
switch_to_default_content
switch_to_frame
switch_to_window
title
window_handles