[Tutor] regular expressions

Danny Yoo dyoo at hkn.eecs.berkeley.edu
Mon Jul 18 07:08:25 CEST 2005

On Sun, 17 Jul 2005, Servando Garcia wrote:

> Using regular expressions how do I represent Floats.

Hi Servando,

I know that you're working on a parser project, but the regex for doing
floats is pretty much a homework project.  There's not much we can do
except point you toward the Regular Expression HOWTO tutorial page:


I'd also strongly recommend that you look at the documentation in the
Python Standard Library, as it does have concrete examples on how to
recognize things like floats here:


Your question is also context-sensitive: what a floating point number
looks like really depends on what kind of language we're modeling.

As a concrete example, in the ML family of languages:


is not a floating-point literal, although it is one in Python, because
it's missing a leading decimal digit.  Conversely, in the Ruby language,


is a floating point literal, although it isn't one in Python, because
Python doesn't allow underscores.  I guess I'm trying to say: some lexical
conventions are not universal:  otherwise, things would be too easy.

You can't assume that everyone uses the same notation for floating point
literals: you need to show examples of what you consider to be floats.
If you want to see Python's specification for floating point literals,


More information about the Tutor mailing list