Normal usage is rather straightforward (where text is page text):

>>> import mwparserfromhell
>>> wikicode = mwparserfromhell.parse(text)

wikicode is a mwparserfromhell.Wikicode object, which acts like an ordinary str object (or unicode in Python 2) with some extra methods. For example:

>>> text = "I has a template! {{foo|bar|baz|eggs=spam}} See it?"
>>> wikicode = mwparserfromhell.parse(text)
>>> print(wikicode)
I has a template! {{foo|bar|baz|eggs=spam}} See it?
>>> templates = wikicode.filter_templates()
>>> print(templates)
>>> template = templates[0]
>>> print(
>>> print(template.params)
['bar', 'baz', 'eggs=spam']
>>> print(template.get(1).value)
>>> print(template.get("eggs").value)

Since nodes can contain other nodes, getting nested templates is trivial:

>>> text = "{{foo|{{bar}}={{baz|{{spam}}}}}}"
>>> mwparserfromhell.parse(text).filter_templates()
['{{foo|{{bar}}={{baz|{{spam}}}}}}', '{{bar}}', '{{baz|{{spam}}}}', '{{spam}}']

You can also pass recursive=False to filter_templates() and explore templates manually. This is possible because nodes can contain additional Wikicode objects:

>>> code = mwparserfromhell.parse("{{foo|this {{includes a|template}}}}")
>>> print(code.filter_templates(recursive=False))
['{{foo|this {{includes a|template}}}}']
>>> foo = code.filter_templates(recursive=False)[0]
>>> print(foo.get(1).value)
this {{includes a|template}}
>>> print(foo.get(1).value.filter_templates()[0])
{{includes a|template}}
>>> print(foo.get(1).value.filter_templates()[0].get(1).value)

Templates can be easily modified to add, remove, or alter params. Wikicode objects can be treated like lists, with append(), insert(), remove(), replace(), and more. They also have a matches() method for comparing page or template names, which takes care of capitalization and whitespace:

>>> text = "{{cleanup}} '''Foo''' is a [[bar]]. {{uncategorized}}"
>>> code = mwparserfromhell.parse(text)
>>> for template in code.filter_templates():
...     if"Cleanup") and not template.has("date"):
...         template.add("date", "July 2012")
>>> print(code)
{{cleanup|date=July 2012}} '''Foo''' is a [[bar]]. {{uncategorized}}
>>> code.replace("{{uncategorized}}", "{{bar-stub}}")
>>> print(code)
{{cleanup|date=July 2012}} '''Foo''' is a [[bar]]. {{bar-stub}}
>>> print(code.filter_templates())
['{{cleanup|date=July 2012}}', '{{bar-stub}}']

You can then convert code back into a regular str object (for saving the page!) by calling str() on it:

>>> text = str(code)
>>> print(text)
{{cleanup|date=July 2012}} '''Foo''' is a [[bar]]. {{bar-stub}}
>>> text == code

(Likewise, use unicode(code) in Python 2.)

For more tips, check out Wikicode's full method list and the list of Nodes.