Do comments slow down an interpreted language?

Question

I am asking this because I use Python, but it could apply to other interpreted languages as well (Ruby, PHP, JavaScript).

Am I slowing down the interpreter whenever

Answer 1

It depends on how the interpreter is implemented. Most reasonably modern interpreters do at least a bit of pre-processing on the source code before any actual execution, and that will include stripping out the comments so they make no difference from that point onward.

At one time, when memory was severely constrained (e.g., 64K total addressable memory, and cassette tapes for storage) you couldn't take things like that for granted. Back in the day of the Apple II, Commodore PET, TRS-80, etc., it was fairly routine for programmers to explicitly remove comments (and even white-space) to improve execution speed. This was also only one of many source code-level hacks routinely employed at the time¹.

Of course, it also helped that those machines had CPUs that could only execute one instruction at a time, had clock speeds around 1 MHz, and had only 8-bit processor registers. Even a machine you'd now find only in a dumpster is so much faster than those were that it's not even funny...

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^{1. For another example, in Applesoft you could gain or lose a little speed depending on how you numbered lines. If memory serves, the speed gain was when the target of a goto statement was a multiple of 16.}