Really-thorough unit tests are the most important technique (yes, I do always aim for 100% coverage), as they also catch many other typos (e.g. where I write + and meant -), off-by-one issues, etc. Integration and load tests exercising every feature are the second line of defense against all kinds of errors (mostly, though, deeper and harder ones;-).
Next are tools such as pylint and pychecker and colorizing editors (I don’t use real IDEs, but they would also help similarly to how my trusty gvim editor does;-).
Techniques such as mandatory code reviews (e.g., cfr a video of an interview of mine on the subject here), while crucial, should focus on other issues — issues that automated tools just won’t catch, such as completeness and correctness of comments/docstrings, choice of good/speedy algorithms, and the like (see here for a summary of the talk I gave on the subject at the same conference as I got that interview at, and a link to the slides’ PDF).