In IPython, I am used to write
function(
and then strike a tab, and get the contents of the docstring and a list of the named argume
Oh, the shortcut is now shift+tab.
Shift-tab only works when you place the edit cursor inside or after the object. Not when it's at the start of the object. This gotcha is not documented anywhere...!
I filed jupyter issue Shift-Tab completion doesn't work when edit cursor is at the start of the object #1902
To display docstrings in Python one can use ? character as a shorthand. 
You can place the ? character before or after (no space allowed) the object you are looking for docs.
To access the source code simply use ?? instead. 
Source: Help and Documentation in IPython