How do I get a decimal value when using the division operator in Python?

Other answers suggest how to get a floating-point value. While this wlil be close to what you want, it won't be exact:

>>> 0.4/100.
0.0040000000000000001

If you actually want a decimal value, do this:

>>> import decimal
>>> decimal.Decimal('4') / decimal.Decimal('100')
Decimal("0.04")

That will give you an object that properly knows that 4 / 100 in base 10 is "0.04". Floating-point numbers are actually in base 2, i.e. binary, not decimal.

Make one or both of the terms a floating point number, like so:

4.0/100.0

Alternatively, turn on the feature that will be default in Python 3.0, 'true division', that does what you want. At the top of your module or script, do:

from __future__ import division

There are three options:

>>> 4 / float(100)
0.04
>>> 4 / 100.0
0.04

which is the same behavior as the C, C++, Java etc, or

>>> from __future__ import division
>>> 4 / 100
0.04

You can also activate this behavior by passing the argument -Qnew to the Python interpreter:

$ python -Qnew
>>> 4 / 100
0.04

The second option will be the default in Python 3.0. If you want to have the old integer division, you have to use the // operator.

Edit: added section about -Qnew, thanks to ΤΖΩΤΖΙΟΥ!