In current version(2.5.11), I've found that openpyxl/compat/init.py may cause memory leakage when using Python 2.7. In line 59
This line will be executed every time a deprecated function is called. But unfortunately python 2.7 will simply append this deprecation type to a global list without checking for duplicates (python 3.x will check for it anyhow). So this will be an issue for those who are using 2.7. I think It is better to move this line outside the function or only execute it once when started.