14. Interactive Input Editing and History Substitution
Some versions of the Python interpreter support editing of the current input line and history substitution, similar to facilities found in the Korn shell and the GNU Bash shell. This is implemented using the GNU Readline library, which supports various styles of editing. This library has its own documentation which we won’t duplicate here.
14.1. Tab Completion and History Editing
Completion of variable and module names is
automatically enabled at interpreter startup so
Tab key invokes the completion function; it looks at
Python statement names, the current local variables, and the available
module names. For dotted expressions such as
string.a, it will evaluate
the expression up to the final
'.' and then suggest completions from
the attributes of the resulting object. Note that this may execute
application-defined code if an object with a
is part of the expression. The default configuration also saves your
history into a file named
.python_history in your user directory.
The history will be available again during the next interactive interpreter
14.2. Alternatives to the Interactive Interpreter
This facility is an enormous step forward compared to earlier versions of the interpreter; however, some wishes are left: It would be nice if the proper indentation were suggested on continuation lines (the parser knows if an indent token is required next). The completion mechanism might use the interpreter’s symbol table. A command to check (or even suggest) matching parentheses, quotes, etc., would also be useful.
One alternative enhanced interactive interpreter that has been around for quite some time is IPython, which features tab completion, object exploration and advanced history management. It can also be thoroughly customized and embedded into other applications. Another similar enhanced interactive environment is bpython.