Why dance around the templating provided by EasyBuild like this?
There are two better alternatives for this:
 * use the `namelower` template, i.e.:
```python
source_urls = [('http://sourceforge.net/projects/%(namelower)s/files/%(namelower)s/%(version)s', 'download')]
```
 * use the `SOURCEFORGE_SOURCE` constant:
```python
source_urls = [SOURCEFORGE_SOURCE]
```

Please use the latter, which is equivalent to `http://download.sourceforge.net/%(namelower)s` (see `eb --avail-easyconfig-templates`), in all Boost easyconfigs. I have a branch ready that does just that, let me know if you'll clean this up or I should open the PR (which will cause conflicts with what you currently have).