Python - how can I define a function from within the Python shell?

Question

>>> def f(x):
...     print x
... f('hello')
  File "<stdin>", line 3
    f('hello')
    ^
SyntaxError: invalid syntax
>>> 

I'm at the prompt in the Python shell. Why doesn't the above code work?

Answer 1

Enter a blank line after "print x". Generally, the ... prompt indicates that Python expects further input for the current block, in this case the function f .

As pointed out by Iguananaut IPython has superior editing capabilities compared to the standard Python shell, for example tab auto completion.

Answer 2

You need to press enter twice after the last line to get back to a >>> prompt in which case you can enter new expressions.

Also, if you're going to by typing lots of multi-line expressions into the interpreter you should give IPython (now with funding!) a look. It supports much better editing of multi-line statements, and even better still if you use the qtconsole or the notebook.