Catching typos in scripting languages

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).

There are errors other than "typos". If you don't test something, knowing that something's found misspelled variable names won't assure you of much anyway.

Some editors (for example, NetBeans) analyse your code and underline "suspicious" parts, for example unused variables, which may be sign of a typo. NB also highlights the identifier above the cursor elsewhere on the screen, which also helps.

Of course, no clever IDE trick can replace proper testing.