import pywikibot
site = pywikibot.Site('test', 'wikipedia')
site
APISite("test", "wikipedia")
page = pywikibot.Page(site, 'test')
page.exists()
True
page.text
'== Hello world! ==\n\n=== One ===\n\n==== Two ====\n\n===== Three ====='
page.save()
Page [[Test]] saved
import pywikibot

site = pywikibot.Site('test', 'wikipedia')
page = pywikibot.Page(site, 'test')

page.text = 'Hello world!'
page.save()
Page [[Test]] saved
help(pywikibot.Page.save)
Help on function save in module pywikibot.page:

save(self, summary=None, watch=None, minor=True, botflag=None, force=False, async=False, callback=None, apply_cosmetic_changes=None, quiet=False, **kwargs, sysop=NotImplemented, comment='[deprecated name of summary]')
    Save the current contents of page's text to the wiki.
    
    @param summary: The edit summary for the modification (optional, but
        most wikis strongly encourage its use)
    @type summary: unicode
    @param watch: Specify how the watchlist is affected by this edit, set
        to one of "watch", "unwatch", "preferences", "nochange":
        * watch: add the page to the watchlist
        * unwatch: remove the page from the watchlist
        * preferences: use the preference settings (Default)
        * nochange: don't change the watchlist
        If None (default), follow bot account's default settings
    
        For backward compatibility watch parameter may also be boolean:
        if True, add or if False, remove this Page to/from bot
        user's watchlist.
    @type watch: string, bool (deprecated) or None
    @param minor: if True, mark this edit as minor
    @type minor: bool
    @param botflag: if True, mark this edit as made by a bot (default:
        True if user has bot status, False if not)
    @param force: if True, ignore botMayEdit() setting
    @type force: bool
    @param async: if True, launch a separate thread to save
        asynchronously
    @param callback: a callable object that will be called after the
        page put operation. This object must take two arguments: (1) a
        Page object, and (2) an exception instance, which will be None
        if the page was saved successfully. The callback is intended for
        use by bots that need to keep track of which saves were
        successful.
    @param apply_cosmetic_changes: Overwrites the cosmetic_changes
        configuration value to this value unless it's None.
    @type apply_cosmetic_changes: bool or None
    @param quiet: enable/disable successful save operation message;
        defaults to False.
        In async mode, if True, it is up to the calling bot to manage the
        ouput e.g. via callback.
    @type quiet: bool