Whitespace is significant in Python. This uncommon syntax rule is one of the refrain of many non-Python programmers about Python. Given most computer languages since Fortran has adopted free layout syntax, this feel like an objectionable design.

Now that I think of it, I find this mostly a problem of wrong framing. The term "whitespace" has already embedded the meaning of unimportant filler. In this sense "significant whitespace" sounds like a problem. Actually the right way to describe it is that Python uses indentation to determine the block structure. Rather than feeling wrong, this is lot more likely to evoke an "aha" reaction from non-Python programmers. Of course it makes a lot sense for the indentation to follow the block structure. I can hardly find any legitimate case for those two to differ.

Austere programmers may notice that there are two way to indicate block structure in main stream languages, by using language construct like "begin" and "end" and by laying out the code using indentation. Whenever there are two ways to do express one thing there will be problem of inconsistency. This extra degree of freedom can get you into trouble sometimes. One of the most nasty class of programming bug is dangling else. It is the case in free layout language when the apparent block structure is different from the actual block structure. Dangling else is not possible in Python. It is because the block structure is determined by the indentation.

2012.06.08 [programming] - comments